frontiers in quantum gases program & abstracts ... - bec … · september 7, 2017 1...

September 7, 2017

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Bose-Einstein Condensation

Frontiers in Quantum Gases

BEC 2017

Program & Abstracts

September 2–8, 2017

Sant Feliu de Guixols, Spain

ORGANIZATION

Scientific Committee

Chair Thierry Giamarchi University of Geneva, Switzerland

Vice Chair Immanuel Bloch Max-Planck-Institut and University Ludwig-Maximilian, Germany

Members Vanderlei Salvador Bagnato University of São Paulo, BrazilPhilippe Bouyer Institut d’Optique Graduate School, FranceCheng Chin University of Chicago, United States of AmericaEric Cornell University of Colorado at Boulder, United States of AmericaAndrew Daley University of Strathclyde, United KingdomEugene Demler Harvard University, United States of AmericaChiara Fort University of Florence, ItalyWolfgang Ketterle Massachusetts Institute of Technology, United States of AmericaServaas Kokkelmans Eindhoven University of Technology, The NetherlandsDeborah S. Jin† University of Colorado at Boulder, United States of AmericaMaciej Lewenstein Institute of Photonic Sciences, SpainHanns-Christoph Nägerl University of Innsbruck, AustriaTilman Pfau University of Stuttgart, GermanyWilliam D. Phillips University of Maryland, United States of AmericaChristophe Salomon Kastler Brossel Laboratory and École Normale Supérieure, FranceYoshiro Takahashi Kyoto University, JapanChristopher Vale Swinburne University of Technology, AustraliaHui Zhai Tsinghua University, ChinaWilhelm Zwerger Technical University of Munich, Germany

Local scientific organizer

Maciej Lewenstein Institute of Photonic Sciences, Spain

Local support

Alexandre Dauphin (ICFO), Miguel Ángel García-March (ICFO), Pjotrs Grišins (UniGE),Aniello Lampo (ICFO), Anne-Maria Visuri (UniGE)

Staff

In Barcelona Sabina Semeraro

In Geneva Christophe Berthod, Adriana Bonito-Aleman, Pascal Cugni, Gregory Manfrini, Natacha Triscone

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SPONSORS

Department of Quantum MatterPhysics, University of Geneva

Switzerland

The Institute of Photonic Sciences

Spain

Max Planck Institutefor Quantum Optics

Germany

Center for Ultracold Atom

United States of America

US Air Force


US Army Research office


InternationalCold Atom Network

France

JILAUniversity of Colorado Boulder


European Laboratory forNon-Linear Spectroscopy

European Union

Institut francilien de recherchesur les atomes froids

France

The Institute of Laser Physics

Germany

Foundations and Applicationsof Quantum Science

Austria

Universität Innsbruck

Austria

Ultracold Quantum MatterEuropean Research Council

European Union

Eidgenössische TechnischeHochschule Zürich

Switzerland

École PolytechniqueUniversité Paris Saclay

France

Quantum Simulations ofInsulators and Conductors

European Union

Bose-Einstein CondensationIstituto Nazionale di Ottica

Italy

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http://dqmp.unige.ch/

https://www.icfo.eu/

https://www.mpg.de/en

https://science.mit.edu/research/ultracold-atoms-center

http://gdr-atomesfroids.cnrs.fr

https://jila.colorado.edu/

http://www.lens.unifi.it/

http://www.ifraf.org/spip.php?article141

http://photon.physnet.uni-hamburg.de/ilp/

https://www.uibk.ac.at/foqus/

https://www.uibk.ac.at/

http://www.uquam.eu/

https://www.ethz.ch/en.html

https://www.polytechnique.edu/fr/paris-saclay

http://www.quic-project.eu/

http://bec.science.unitn.it/infm-bec/research/research.html

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CONFERENCE PROGRAM

September 2 (Sat)

Arrival and registration

September 3 (Sun)

Conference opening 08:30 – 08:45

September 3 (Sun) 08:45 – 10:30

Session 1: New phases of BECChair: A. Aspect (Institut d’Optique Graduate School)

08:45 – 09:20 Spin-orbit coupling and the supersolid stripe phase of Bose-Einstein condensatesW. Ketterle (Department of Physics, MIT-Harvard Center for Ultracold Atoms)

09:20 – 09:55 Supersolid Goldstone and Higgs modesT. Esslinger (ETH Zurich)

09:55 – 10:30 Quantum droplets in attractive Bose-Bose mixturesL. Tarruell (ICFO – The Institute of Photonic Sciences)

Coffee 10:30 – 11:15

September 3 (Sun) 11:15 – 12:25

Session 2: Polarons and connected subjectsChair: C. Kollath (University of Bonn)

11:15 – 11:50 Observation of the Bose polaron and fluctuations of Bose-Einstein condensatesJ. Arlt (Institut for Fysik og Astronomi, Aarhus Universitet)

11:50 – 12:25 Exploring magnetic polarons with cold atoms: From Kondo effect to the Fermi Hubbard modelE. Demler (Harvard University)

Lunch 12:30 – 14:00

September 3 (Sun) 15:45 – 17:30

Session 3: Gauge fields and topological bandsChair: N. Cooper (University of Cambridge)

15:45 – 16:20 Chern numbers counted in a synthetic-dimension quantum Hall stripI. Spielman (Joint Quantum Institute: NIST and UMD)

16:20 – 16:55 Topology and dynamics in Floquet driven optical latticesK. Sengstock (Universität Hamburg)

16:55 – 17:30 Geometric origin of flat band superfluidity, and Bose-Einstein condensation in a plasmoniclatticeP. Törmä (COMP Centre of Excellence, Aalto University)

Coffee 17:30 – 18:00

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September 3 (Sun) 18:00 – 19:25

Session 4: BEC prize sessionChair: C. Salomon (École Normale Supérieure, Laboratoire Kastler Brossel)

18:00 – 18:05 The Toptica companyW. Kaenders (TOPTICA Photonics AG)

18:05 – 18:10 Senior prize citation

18:10 – 18:45 Revisiting BKT physics with uniform gasesJ. Dalibard (Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL Research University,UPMC-Sorbonne Universités)

18:45 – 18:50 Junior prize citation

18:50 – 19:25 Inflationary dynamics for Bose-Einstein condensates driven crossing a quantum critical pointC. Chin (University of Chicago)

Dinner 19:30 – 21:00

September 4 (Mon)

September 4 (Mon) 08:30 – 10:30

Session 5: The quantum-gas legacy of Debbie JinChair: M. Inguscio (University of Florence)

08:30 – 08:45 AddressW. D. Phillips (JQI–NIST and University of Maryland)

08:45 – 09:20 An Efimov population: A few-body coda to a many-body opusE. Cornell (JILA, NIST, University of Colorado, Boulder)

09:20 – 09:55 Stable ferromagnetism in a weakly interacting quantum degenerate Fermi gas: Exploring apathway first opened by DebbieA. M. Rey (JILA, NIST and Department of Physics, University of Colorado, Boulder)

09:55 – 10:30 The making of a polar molecule quantum gasJ. Ye (JILA, NIST, University of Colorado, Boulder)

Coffee 10:30 – 11:15

September 4 (Mon) 11:15 – 12:25

Session 6: Impurities in quantum gasesChair: J. Selim (Universität Heidelberg)

11:15 – 11:50 Universality and dynamics of impurities in quantum gasesM. Parish (Monash University)

11:50 – 12:25 Impurities strongly interacting with a Fermi seaR. Grimm (IQOQI Innsbruck, Austrian Academy of Sciences)

Lunch 12:30 – 14:00

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September 4 (Mon) 15:45 – 17:30

Session 7: Long range interactionsChair: D. Stamper-Kurn (University of California, Berkeley)

15:45 – 16:20 Experimental many-body physics using arrays of individual Rydberg atomsA. Browaeys (Laboratoire Charles Fabry, Institut d’Optique)

16:20 – 16:55 Latest results on dipolar phenomena in Erbium quantum gasesF. Ferlaino (University of Innsbruck, Institute for Quantum Optics and Quantum Information)

16:55 – 17:30 Dipolar quantum gases and liquidsT. Pfau (Physikalisches Institut and Center for Integrated Quantum Science and Technology)

Coffee 17:30 – 18:15

September 4 (Mon) 18:15 – 19:25

Session 8: Thermalization and dissipationChair: J. Schmiedmayer (Technische Universität Wien)

18:15 – 18:50 Quantum thermalization dynamics with matrix-product statesE. Altman (University of California Berkeley)

18:50 – 19:25 Bose-Einstein condensates in imaginary potentialsH. Ott (Department of Physics, University of Kaiserslautern)

Dinner 19:30 – 21:00

September 4 (Mon) 21:00 – 23:00

Poster session 1

September 5 (Tue)

September 5 (Tue) 08:45 – 10:30

Session 9: Fermion microscopeChair: Y. Takahashi (Kyoto University)

08:45 – 09:20 A cold-atom Fermi-Hubbard antiferromagnetM. Greiner (Harvard University)

09:20 – 09:55 Exploring quantum magnetism at the single spin and atom levelC. Gross (Max Planck Institute)

09:55 – 10:30 Strongly correlated Fermi gases under the microscopeM. Zwierlein (Massachusetts Institute of Technology)

Coffee 10:30 – 11:15

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September 5 (Tue) 11:15 – 12:25

Session 10: Fermionic systemsChair: P. Vignolo (Institut de Physique de Nice)

11:15 – 11:50 Bose-Fermi dual superfluidsC. Salomon (École Normale Supérieure, Laboratoire Kastler Brossel)

11:50 – 12:25 Excitations and non-equilibrium physics of strongly interacting Fermi gasesM. Koehl (University of Bonn)

Lunch 12:30 – 14:00

Excursion and banquet

14:45 Bus departure direction Dali museum in front of the hotel main entrance

16:30 – 19:00 Visit of the Dali museum in Figueres (2h30 guided tour)

18:00 Bus departure direction El Pa Volador in front of the hotel main entrance

19:00 Bus departure direction El Pa Volador from Dali museum

19:30 Banquet in restaurant El Pa Volador

September 6 (Wed)

September 6 (Wed) 08:45 – 10:30

Session 11: PolaritonsChair: N. Proukakis (Newcastle University, Joint Quantum Centre Durham-Newcastle)

08:45 – 09:20 Exciton-polariton condensation in non-Hermitian potentialsE. Ostrovskaya (Nonlinear Physics Centre, Research School of Physics & Engineering, The AustralianNational University)

09:20 – 09:55 Cavity polariton lattices: A non-linear photonic emulatorJ. Bloch (Centre de Nanosciences et de Nanotechnologies (C2N) CNRS, Univ. Paris-Sud, UniversitéParis-Saclay)

09:55 – 10:30 Photons and atoms in synthetic magnetic fields and synthetic dimensionsI. Carusotto (INO-CNR BEC Center and Dipartimento di Fisica, Universitá di Trento)

Coffee 10:30 – 11:15

September 6 (Wed) 11:15 – 12:25

Session 12: Dynamics of quantum systemsChair: J. Thywissen (University of Toronto)

11:15 – 11:50 Dissipative and coherent dynamics in a Josephson junction between fermionic superfluidsG. Roati (CNR-INO, LENS, University of Florence)

11:50 – 12:25 Two rigorous results on dynamics of quantum systemsH. Zhai (Tsinghua University)

Lunch 12:30 – 14:00

8

September 6 (Wed) 15:45 – 17:30

Session 13: Bell correlationsChair: A. Fetter (Stanford University)

15:45 – 16:20 EPR and spatial-mode entanglement in spinor Bose-Einstein condensatesC. Klempt (Institut für Quantenoptik, Leibniz Universität Hannover)

16:20 – 16:55 Detecting the nonlocality of many-body quantum statesM. Lewenstein (ICFO – Institut de Ciencies Fotoniques and The Barcelona Institute of Science andTechnology)

16:55 – 17:30 Atomic spin entanglement and anyonic fractional statistics in a spin-dependent optical super-latticeZ.-S. Yuan (University of Science an Technology of China)

Coffee 17:30 – 18:15

September 6 (Wed) 18:15 – 19:25

Session 14: Bosons: dimensionality and correlationsChair: H. Perrin (CNRS, Paris 13 University)

18:15 – 18:50 Studying superfluidity with ultracold atom circuitsG. Campbell (Joint Quantum Institute, NIST and UMD)

18:50 – 19:25 Strongly interacting bosonsZ. Hadzibabic (University of Cambridge)

Dinner 19:30 – 21:00

September 6 (Wed) 21:00 – 23:00

Poster session 2

September 7 (Thu)

September 7 (Thu) 08:45 – 10:25

Session 15: Hot topicsChair: S. Stringari (University of Trento)

08:45 – 09:10 Microscopy of atomic Fermi-Hubbard systems in new regimesW. Bakr (Princeton University)

09:10 – 09:35 Probing many-body dynamics on a 51-atom quantum simulatorH. Bernien (Harvard University)

09:35 – 10:00 Negative-mass quantum hydrodynamics with spin-orbit coupled BECsP. Engels (Washington State University)

10:00 – 10:25 Bell correlations in a Bose-Einstein condensateP. Treutlein (University of Basel)

Coffee 10:25 – 11:10

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September 7 (Thu) 11:10 – 12:25

Session 16: Hot topicsChair: T.-L. Ho (The Ohio State University)

11:10 – 11:35 Thermalized light in variable micropotentials and coupled photon condensatesJ. Schmitt (Universität Bonn)

11:35 – 12:00 A single atom probe of lattice gases in momentum spaceD. Clément (Institut d’Optique Graduate School)

12:00 – 12:25 A photon-photon quantum gate based on Rydberg polaritonsS. Dürr (MPI for Quantum Optics)

Lunch 12:30 – 14:00

September 7 (Thu) 15:45 – 17:30

Session 17: New directionsChair: G. Shlyapnikov (CNRS and CEA)

15:45 – 16:20 Observation of quantum Hawking radiation and its entanglement in an analogue black holeJ. Steinhauer (Technion)

16:20 – 16:55 Scrambling quantum information in cold atoms with lightM. Schleier-Smith (Stanford University)

16:55 – 17:30 Creating materials from light: Landau levels, Mott insulators, and Laughlin puddlesJ. Simon (University of Chicago)

Coffee 17:30 – 18:15

September 7 (Thu) 18:15 – 19:25

Session 18: Pairing in fermionic systemsChair: W. Zwerger (TU Munich)

18:15 – 18:50 Excitation spectra of near-homogeneous Fermi gasesC. Vale (Swinburne University of Technology)

18:50 – 19:25 1D–3D crossover of a spin-imbalanced Fermi gasR. Hulet (Rice University)

Dinner 19:30 – 21:00

September 7 (Thu) 21:00 – 23:00

Poster session 3

End of the Conference

10

POSTER SESSIONSPosters 1 to 24 are located in the conference room

Posters 25 to 49 are located in the Goya roomThe board size is 1.5 m× 1.0 m (height × width)

September 4 (Mon) 21:00 – 23:00

Poster session 1

Ahufinger Veronica High-efficient adiabatic transport of a Bose-Einstein condensate in coupledwell potentials

1-1

Andreev Sergey Fragmented supersolid of dipolar excitons 1-2

Baranov Mikhail Creation and application of nanoscale optical barriers 1-3

Barberan Nuria Few particle systems: An exact analysis of the fractional quantum Hall effect 1-4

Mazzanti Ferran Droplets formation in trapped systems of dipolar bosons 1-5

Cabrera-Gutiérrez Citlali Bose-Einstein condensates in a phase-modulated optical lattice 1-6

Castin Yvan Phonon damping in a pair-condensed Fermi gas 1-7

Celi Alessio Topological properties and many-body phases of synthetic Hofstadter strips 1-8

Chapman Michael Quench dynamics and excitation modes of a quantum phase transition in aspin-1 BEC

1-9

Daley Andrew Novel spin dynamics and transport with cold atoms in tilted optical lattices 1-10

Dalmonte Marcello Many-body localization dynamics from gauge invariance 1-11

Engels Peter Supersolid-like states in a spin-orbit coupled Bose-Einstein condensate 1-12

Fallani Leonardo Engineering topological states of matter with ultracold two-electron atoms 1-13

Fetter Alexander Vortex dynamics on a cylinder 1-14

Foerster Angela Integrable quantum tunneling models in ultracold physics 1-15

Ruostekoski Janne Giant many-body subradiant excitations in cold atomic ensembles 1-16

Gajda Mariusz Few-body systems in a single-shot picture: Pauli crystals 1-17

García-March Miguel Á. Open quantum dynamics of two distinguishable particles in a BEC 1-18

Gardiner Simon Raman transfer of knotted optical vortices onto atomic Bose-Einstein con-densates

1-19

Hannaford Peter Simulating quantum spin models using ultracold Rydberg-excited ensem-bles in magnetic microtrap arrays

1-20

Hauke Philipp Quantum simulation of lattice gauge theories in cold atoms 1-21

Iemini Fernando Majorana quasi-particles protected by Z2 angular momentum conservation 1-22

Jachymski Krzysztof Controlling the quantum fluctuations of strongly magnetic atoms 1-23

Jamison Alan Experiments with ultracold triplet ground-state molecules 1-24

Kjærgaard Niels Cold collision experiments at Feshbach resonances far above threshold 1-25

Lampo Aniello Bose polaron as an instance of quantum Brownian motion 1-26

Lamporesi Giacomo Vortex reconnections and rebounds in trapped atomic Bose-Einstein conden-sates

1-27

Massignan Pietro Bose polarons at finite temperature and strong coupling 1-28

Mathey Ludwig Detecting topological defects and implementing supersymmetric quantummechanics

1-29

Mazza Leonardo Laughlin-like states in bosonic and fermionic 1D gases with synthetic di-mension

1-30

Naidon Pascal Two impurities in a BEC: From Yukawa to Efimov attracted Bose polarons 1-31

11

Oktel Mehmet Hofstadter butterfly evolution in the space of two-dimensional Bravais lat-tices

1-32

Papoular David Entangling two non-identical atoms via Rydberg blockade 1-33

Pelster Axel Two intriguing examples for topological effects in ultracold atoms 1-34

Rasel Ernst M. Space-born Bose-Einstein condensation for precision interferometry 1-35

Rizzi Matteo Exploring interacting topological insulators with ultracold atoms: The syn-thetic Creutz-Hubbard model

1-36

Sacha Krzysztof Time crystals 1-37

Sagi Yoav Many-body localization in system with a completely delocalized single-particle spectrum

1-38

Sanchez-Palencia Laurent Superfluid-insulator transitions for strongly interacting one-dimensionalbosons in a shallow periodic and disordered potentials

1-39

Sanpera Anna Novel method to study disordered frustrated antiferromagnets in opticallattices

1-40

Santos Luis Quantum fluctuations in low-dimensional dipolar condensates 1-41

Stringari Sandro Angular momentum in spin-orbit coupled Bose-Einstein condensed gases 1-42

Schmiedmayer Jörg Recurrences in an isolated quantum many-body system 1-43

Takahashi Yoshiro Non-equilibrium dynamics of ultracold atoms in optical lattices studied withYtterbium atoms

1-44

Vale Chris Quantum anomaly and thermodynamics of a 2D Fermi gas via collectiveoscillations

1-45

van der Straten Peter Faraday excitations in a Bose-Einstein condensate 1-46

Weitenberg Christof Observation of a dynamical topological phase transition in the non-equilibrium dynamics of ultracold quantum gases in driven optical lattices

1-47

Zaccanti Matteo Exploring itinerant ferromagnetism with ultracold repulsive Fermi mixtures 1-48

Zillich Robert Dynamics of quantum many-body systems far from equilibrium: Interactionquenches

1-49

Pupillo Guido Cavity-enhanced transport of charge 1-50

September 6 (Wed) 21:00 – 23:00

Poster session 2

Ardila Luis A. Peña Impurities immersed in a BEC: Quantum simulator of the polaron? 2-1

Ashida Yuto Parity-time-symmetric quantum critical phenomena 2-2

Bornheimer Ulrike Artificial gauge fields in the honeycomb lattice 2-3

Boulier Thomas Spontaneous avalanche dephasing in large Rydberg ensembles 2-4

Bourdel Thomas Nonlinear scattering of atomic bright solitons in disorder 2-5

Bouyer Philippe Ultracold atoms trapped in subwavelength potentials 2-6

Chapurin Roman Efimov physics in resonantly interacting Bose gases 2-7

Chen Shuai 2D spin-orbit coupling for Rb BEC 2-8

Chevy Frédéric Critical velocity of counterflowing superfluids 2-9

Chomaz Lauriane Dipolar macro-droplet of Erbium stabilized by quantum fluctuations 2-10

Citro Roberta Vortex lattice melting in a boson ladder in artificial gauge field 2-11

Dauphin Alexandre Detection of Zak phases and topological invariants in a chiral quantum walkof twisted photons

2-12

Davis Matthew Minimal model for bistability in a driven-dissipative superfluid 2-13

Fischer Uwe R. Phase-fluctuating condensates are fragmented: An experimental bench-mark for self-consistent quantum many-body calculations

2-14

12

Fleischhauer Michael Topological order in finite-temperature and driven dissipative systems 2-15

Garraway Barry RF-dressed atom wave-guides, shells and lattices for quantum technologyapplications: Test of Landau-Zener theory

2-16

Genkina Dina Bulk topology of thin quantum Hall ribbons 2-17

Goldman Nathan Probing topology by “heating” 2-18

Gordillo María Carmen Fermionization and Mott insulator formation in few-fermion clusters in one-dimensional optical lattices

2-19

Heidrich-Meisner Fabian Unusual transport properties of the 1D Fermi-Hubbard model 2-20

Inoue Ryotaro Noncooled site-resolved imaging of a Mott insulator 2-21

Jiménez García Karina One-dimensional spinor Bose gases: Magnetic order and non-equilibriumdynamics

2-22

Kokkelmans Servaas Three-body physics with finite-range potentials 2-23

Lev Benjamin Breaking integrability in a dipolar quantum Newton’s cradle 2-24

Levinsen Jesper Bose polarons 2-25

Modugno Michele Simulating condensed matter with ultracold atoms: The Haldane model andthe Peierls substitution

2-27

Mompart Jordi Dynamics of orbital angular momentum states of ultracold atoms in ringpotentials

2-28

Olshanii Maxim Quantum Galilean cannon as a Schrödinger cat 2-29

Perrin Hélène Probing superfluidity in a quasi two-dimensional Bose gas through its localdynamics

2-30

Poletti Dario Energy transport in bosonic ladders: Interplay between interactions, gaugefield and geometry of system-bath coupling

2-31

Preiss Philipp Quantum simulation of mesoscopic Fermi systems 2-32

Robins Nick A precision quantum sensor based on free falling Bose-Einstein condensates 2-33

Roscilde Tommaso Studying quantum criticality with quantum observables in cold-atom exper-iments

2-34

Schmiedmayer Jörg Experimental characterization of a quantum many-body system via higher-order correlations

2-35

Schneider Ulrich An optical quasicrystal for ultracold atoms 2-36

Semeghini Giulia Quantum liquid droplets in a Bose-Bose mixture of ultracold atoms 2-37

Sheikhan Ameneh Cavity-induced generation of non-trivial topological states in quasi-one-dimensional and two-dimensional Fermi gas

2-38

Shlyapnikov Georgy Two-dimensional finite-temperature bosonic atoms in disorder 2-39

Thywissen Joseph AC conductivity measurement of ultracold fermions in an optical lattice 2-40

Uchino Shun Anomalous transport in attractively interacting Fermi gases 2-41

van Druten Klaasjan Rydberg excitation and Rydberg dressing of ultracold gases on an atom chip 2-42

Vernac Laurent Mean field and beyond mean field spin mixing dynamics in Chromium quan-tum gases

2-43

Werner Félix Controlled summation of diagrammatic series for the unitary Fermi gas:Bold diagrammatic Monte Carlo, large-order asymptotics and conformal-Borel transformation

2-44

Yamamoto Ryuta A quantum gas microscope of two-electron atoms with fluorescence andFaraday imaging

2-45

Zakrzewski Jakub Many-body localization transition for bosons in optical lattice 2-46

Zwerger Wilhelm Deep inelastic scattering on ultracold atoms 2-47

13

September 7 (Thu) 21:00 – 23:00

Poster session 3

Astrakharchik Grigory Ultradilute low-dimensional liquids 3-1

Brand Joachim Dark solitons and vortices in confined superfluids 3-2

Brantut Jean-Philippe Quantum coherent transport of cold fermions in mesoscopic structures 3-3

Bruun Georg Induced interactions and topological phases in Fermi-Bose mixtures 3-4

Busch Thomas Creating and controlling superfluid vortex rings in artificial magnetic fields 3-5

Corman Laura Thermoelectric transport through an atomic quantum point contact 3-6

Cornish Simon Coherent control of ultracold RbCs molecules in an optical trap 3-7

De Marco Luigi New frontiers in the manipulation and probing of ground state polarmolecules

3-8

DeSalvo Brian Dual-degeneracy in a Bose-Fermi mixture with extreme mass imbalance 3-9

Fletcher Richard Two- and three-body contacts in the unitary Bose gas 3-10

Görlitz Axel A transport apparatus for mixed quantum gases with Yb and Rb 3-11

Greif Daniel Observation of antiferromagnetic long-range order in the Hubbard modelwith ultracold atoms

3-12

Grišins Pjotrs Transport properties of ultracold interacting fermions in a mesoscopic lat-tice

3-13

Hodgman Sean Ghost imaging and solving the many-body problem using strongly corre-lated atoms from s-wave collision halos

3-14

Hoinka Sascha Goldstone mode and pair-breaking excitations in atomic Fermi superfluids 3-15

Hu Hui Superfluid density and critical velocity near the fermionic Berezinskii-Kosterlitz-Thouless transition

3-16

Iskin Menderes BCS theory of time-reversal-symmetric Hofstadter-Hubbard model 3-17

Jukic Dario Momentum distribution and “free” expansion of an anyonic gas 3-18

Juzeliunas Gediminas Semi-synthetic zigzag lattices 3-19

Kolodrubetz Michael Topological Floquet-Thouless energy pump 3-20

Lim Lih-King Quantum charge pumps with topological phases in Creutz ladder 3-21

Liu Xia-Ji Traveling Majorana solitons in a low-dimensional spin-orbit-coupled Fermisuperfluid

3-22

Moritz Henning Two-dimensional homogeneous Fermi gases 3-23

Möttönen Mikko Tying quantum knots 3-24

Orus Roman A simple tensor network algorithm for 2D steady states 3-25

Proukakis Nick Dynamical quenched equilibration across the BEC phase transition in atrapped quantum gas

3-26

Prüfer Maximilian Observation of self-similar dynamics in a one-dimensional spinor Bose-Einstein condensate

3-27

Gaj Anita Superfluid in a shaken optical lattice: Quantum critical dynamics and topo-logical defect engineering

3-28

Ruseckas Julius Phase-space curvature in spin-orbit-coupled ultracold atomic systems 3-30

Schmiedmayer Jörg Dephasing and relaxation of bosons in 1D: Newton’s cradle revisited 3-31

Simula Tapio Vortex mass in a superfluid 3-32

Smith Robert Quantum dynamics of a Bose gas quenched to unitarity 3-33

Sols Fernando Generation of atypical hopping and interactions by kinetic driving 3-34

Stamper-Kurn Dan Quantum gases in cavities and lattices 3-35

Stringari Sandro Spin superfluidity of a Bose gas mixture at finite temperature 3-36

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Struck Julian Strongly interacting homogeneous Fermi gases 3-37

Tsatsos Marios C. Granulation in Bose-Einstein condensates as manifestation of quantum fluc-tuations

3-38

Unal F. Nur Engineering an optical solenoid for quantum gases 3-39

Vignolo Patrizia Momentum distribution and symmetry characterization of one-dimensionalstrongly interacting Fermi gases

3-40

Visuri Anne-Maria Impurity and soliton dynamics in a Fermi gas with nearest-neighbor inter-actions

3-41

von Klitzing Wolf Atomtronics with adiabatic potentials 3-42

White Angela Necklace-like states in toroidally trapped Rashba spin-orbit coupled Bose-Einstein condensates

3-43

Will Sebastian Towards ultracold dipolar molecules in two dimensions 3-44

Yakaboylu Enderalp Emergence of non-abelian magnetic monopoles in a quantum impurity prob-lem

3-45

Zibold Tilman Spatial entanglement and Einstein-Podolsky-Rosen steering in a Bose-Einstein condensate

3-46

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ABSTRACTSof the

oral presentations

BEC 2017 – Bose-Einstein Condensation Sant Feliu de Guixols, SpainFrontiers in Quantum Gases September 2–8, 2017

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Spin-orbit coupling and the supersolid stripe phase of Bose-Einsteincondensates

Wolfgang Ketterle

Department of Physics, MIT-Harvard Center for Ultracold Atoms

A supersolid is an unusual form of matter which combines the property of superfluid flow with thelong-range spatial periodicity of solids. Though long predicted, the observation in solid Helium hasbeen elusive. The concept of supersolidity was generalized to include other superfluid systems whichbreak the translational symmetry of space. One candidate has been a Bose-Einstein condensate withspin-orbit coupling where the stripe phase features a density modulation. We recently reported the firstobservation of this modulated density. For this, we used a novel spin-orbit coupling scheme developedin our previous work [1] where the two pseudospins are the two lowest states in a lattice of doublewells (superlattice). The new scheme allowed us to not only increase the contrast of the stripes but alsogave us a background free signal. The associated density modulation was directly probed with Braggscattering.

[1] J. Li et. al., Phys. Rev. Lett. 117, 185301 (2016).

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Supersolid Goldstone and Higgs modes

Tilman Esslinger

ETH Zurich, Otto-Stern-Weg 1, 8093 Zürich, Switzerland

The concept of a supersolid state is paradoxical. It combines the crystallization of a many-body systemwith dissipationless flow of the atoms it is built of. This quantum phase requires the breaking of twosymmetries, the phase invariance of a superfluid and the translational invariance to form the crystal. Weexperimentally studied two forms of supersolids: i) a lattice supersolid, breaking a discrete translationalsymmetry. This bosonic lattice model features competing short- and long-range interactions, and weobserved the appearance of four distinct quantum phases—a superfluid, a supersolid, a Mott insulatorand a charge density wave. The system is based on an atomic quantum gas trapped in an opticallattice inside a single high-finesse optical cavity [1]. ii) Recently, we succeeded in realizing a supersolidbreaking a continuous translational symmetry. This symmetry emerges from two discrete spatial onesby symmetrically coupling a Bose-Einstein condensate to the modes of two optical cavities [2]. We havenow also been able to identify and monitor the Higgs and the Goldstone and Higgs Modes in the system[3].

[1] R. Landig, L. Hruby, N. Dogra, M. Landini, R. Mottl, T. Donner, and T. Esslinger, Nature 532, 476 (2016).

[2] J. Léonard, A. Morales, P. Zupancic, T. Esslinger, and T. Donner, Nature 543, 87 (2017).

[3] Julian Léonard, Andrea Morales, Philip Zupancic, Tobias Donner, and Tilman Esslinger, arXiv:1704.05803 (2017).

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Quantum droplets in attractive Bose-Bose mixtures

Leticia Tarruell

ICFO-The Institute of Photonic Sciences, Castelldefels (Barcelona), Spain

Dilute quantum droplets are liquid-like clusters of ultra-cold atoms self-trapped by attractive mean-fieldforces, and stabilized against collapse by repulsive beyond mean-field many-body effects. Originallypredicted for mixtures of Bose-Einstein condensates with attractive interactions [1], these systems havebeen recently realized in dipolar quantum gases [2–5]. We exploit a mixture of two 39K Bose-Einsteincondensates with attractive inter-state and repulsive intra-state interactions to experimentally explorethe physics of quantum droplets in two different geometries.For a gas confined only along the vertical direction, we observe droplets self-bound along the radialdirection, which evaporate into an expanding gas below a critical atom number due to the quantumpressure of their constituents. We experimentally map out the liquid-to-gas transition as a function ofatom number and interaction strength, and compare it to a simple theoretical model.For a gas confined in a quasi-one dimensional geometry, two types of self-bound states exist: solitons,stabilized by quantum pressure, and droplets, stabilized by quantum fluctuations. Depending on theatom number and interaction strength, they are separated either by an abrupt transition or by a smoothcrossover, a situation that we explore experimentally.

[1] D. S. Petrov, Phys. Rev. Lett. 115, 155302 (2015).

[2] H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, and T. Pfau, Nature 530, 194 (2016).

[3] I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, and T. Pfau, Phys. Rev. Lett. 116, 215301 (2016).

[4] L. Chomaz, S. Baier, D. Petter, M. J. Mark, F. Wächtler, L. Santos, and F. Ferlaino, Phys. Rev. X 6, 041039 (2016).

[5] M. Schmitt, M. Wenzel, F. Böttcher, I. Ferrier-Barbut, and T. Pfau, Nature 539, 259 (2016).

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Observation of the Bose polaron and fluctuations of Bose-Einstein condensates

Jan Arlt

Institut for Fysik og Astronomi, Aarhus Universitet, 8000 Aarhus C, Denmark

The behavior of a mobile impurity particle interacting with a quantum-mechanical medium is offundamental importance. This scenario was previously realized experimentally in pure fermionicsystems, however there had not been a realization in a bosonic environment. Our investigation of theBose polaron is based on the realization of 39K Bose-Einstein condensates (BECs) in the vicinity of threeFeshbach resonances. These resonances allow for the condensation of 39K and enable tuning of thescattering length between atoms in the (F = 1, mF = −1) and (1,0) states. We measure the energyof an impurity interacting with the BEC by performing radio frequency spectroscopy between thesestates. Our results are in good agreement with theories that incorporate three-body correlations, bothin the weak-coupling limits and across unitarity. I addition I will briefly discuss current experimentstowards the observation of fundamental fluctuations in interacting BECs. By using non-destructivemeasurements and feedback within an experimental sequence we achieve run to run stability of the finalatom number at the shot noise limit in thermal ensembles. This is the basis for our current investigationof fluctuations in BECs.

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Exploring magnetic polarons with cold atoms: From Kondo effect to the FermiHubbard model

Eugene Demler

Harvard University

I will discuss how one can use ultracold atoms in optical lattices to explore the interplay of spin andcharge degrees of freedom in paradigmatic models of quantum magnetism. Examples include analysisof the Fermi Hubbard model in a quantum microscope and realization of Kondo effect with alkalineearth atoms.

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Chern numbers counted in a synthetic-dimension quantum Hall strip

Ian Spielman

Joint Quantum Institute: NIST and UMD

We engineered a two-dimensional magnetic lattice in an elongated strip geometry, with effective per-plaquette flux about 4/3 times the flux quanta. The long direction of this strip is formed from a 1Doptical lattice while the short direction is built from the 5 mF states comprising the f = 2 ground statehyperfine manifold of 87Rb. We imaged the localized edge and bulk states of atomic Bose-Einsteincondensates in this strip, with single lattice-site resolution along the narrow direction. In this 5-site widestrip we are able to delineate between bulk behavior quantified by Chern numbers and edge behaviorwhich is not.

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Topology and dynamics in Floquet driven optical lattices

Klaus Sengstock

Universität Hamburg

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Geometric origin of flat band superfluidity, and Bose-Einstein condensation in aplasmonic lattice

T. K. Hakala,1 A. J. Moilanen,1 S. Peotta,1 L. Liang,1 A. Julku,1 A. I. Väkeväinen,1 T. I. Vanhala,1 R. Guo,1

J.-P. Martikainen,1 K. S. Daskalakis,1 H. T. Rekola,1 M. Tovmasyan,2 S. D. Huber,2 T. Siro,1 A. Harju,1

D-H. Kim,3 and P. Törmä1

1 COMP Centre of Excellence, Department of Applied Physics, Aalto University, Finland2 Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland

3 Dept of Physics and Photon Science, Gwangju Institute of Science and Technology, Korea

Results on two separate topics are presented: theory results on flat-band superfluidity, and experimentalobservation of a Bose-Einstein condensate in a plasmonic lattice.Fermions in flat bands are predicted to reach non-zero pairing gaps at high temperatures. Superfluidity,however, has been an open question in flat bands since the usual group velocity is zero. We showtheoretically and numerically that superfluidity in a flat band is possible whenever the band has anon-zero Berry curvature [1]. We discover a geometric contribution to the superfluid weight and ananomalous term in the supercurrent, proportional to the quantum metric. Quantum metric is the realpart of the quantum geometric tensor whose imaginary part is the Berry curvature. Our results indicatethat also the real part has an important role in physical phenomena.We experimentally observe a Bose–Einstein condensate (BEC) of surface plasmon polaritons in latticemodes of a metal nanoparticle array [2]. Interaction of the nanoscale-confined surface plasmons witha room-temperature bath of dye molecules enables thermalization and condensation in picoseconds.The ultrafast thermalization and condensation dynamics are revealed by an experiment that exploitsitinerant thermalization and the open cavity character of the system. Fit to the BE-distribution at roomtemperature, spectral narrowing, non-linear behaviour at critical density, as well as the onset and growthof spatial coherence were observed. A crossover from BEC to usual lasing is realized by tailoring theband structure.

[1] S. Peotta and P. Törmä, Nat. Comm. 6, 8944 (2015); A. Julku, S. Peotta, T. I. Vanhala, D-H. Kim, and P. Törmä, Phys. Rev.

Lett. 117, 045303 (2016); M. Tovmasyan, S. Peotta, P. Törmä, and S. D. Huber, Phys. Rev. B 94, 245149 (2016); L. Liang, T. I.

Vanhala, S. Peotta, T. Siro, A. Harju, and P. Törmä, Phys. Rev. B 95, 024515 (2017); L. Liang, S. Peotta, A. Harju, and P. Törmä,

arXiv:1705.04542 (2017).

[2] T. K. Hakala, A. J. Moilanen, A. I. Väkeväinen, R. Guo, J.-P. Martikainen, K. S. Daskalakis, H. T. Rekola, A. Julku, and P. Törmä,

arXiv:1706.01528 (2017).

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Revisiting BKT physics with uniform gases

Jean Dalibard

Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL Research University, UPMC-Sorbonne Universités, 11 place Marcelin

Berthelot, 75005 Paris

The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes how topological order can emerge in alow-dimensional system when it is cooled below its critical temperature. In particular, it is relevant foraddressing the physics of 2D gases of atoms, molecules and photonic systems.However most experimental studies that have been performed so far deal with harmonically trappedsystems, for which it remains difficult to characterize some key features of BKT physics. In this talk Iwill describe recent experiments performed with uniform gases of Rb atoms, which make it possible toaccess such features, from second sound propagation to quasi-long range order and out-of-equilibriumphenomena.This work is supported by ERC (Synergy grant UQUAM), ANR and IFRAF.

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Inflationary dynamics for Bose-Einstein condensates driven crossing a quantumcritical point

Cheng Chin

University of Chicago

Quantum phase transitions are transitions between distinct many-body ground states, and are of extensiveinterest in research ranging from condensed matter physics to cosmology. Key features of the phasetransitions include a stage with rapidly growing new order, called inflation in cosmology, followed bythe formation of topological defects. We report the observation of coherent inflationary dynamics acrossa quantum critical point in driven Bose-Einstein condensates. The inflation manifests in the exponentialgrowth of density waves and populations in well-resolved momentum states. After the inflation stage,extended coherent dynamics is evident in both real and momentum space. We present an intuitivedescription of the quantum critical dynamics in our system and demonstrate the essential role of phasefluctuations in the formation of topological defects.

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An Efimov population: A few-body coda to a many-body opus

Eric Cornell

University of Colorado Boulder

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Stable ferromagnetism in a weakly interacting quantum degenerate Fermi gas:Exploring a pathway first opened by Debbie

Ana Maria Rey

JILA, NIST and Department of Physics, University of Colorado, Boulder

Quantum degenerate Fermi gases, realized for the first time at JILA in the group of Debbie Jin, havedemonstrated great potential for the emulation of strongly correlated models featuring local interactions.In this talk I will argue that these systems are also ideal quantum emulators of spin-models withlong-range interactions, a new frontier in atomic physics. In particular I will discuss the experimentalrealization of a spin lattice model with all-to-all Heisenberg-type interactions in a gas Fermi gas of40K atoms. We studied the competition between interactions and spin-motional dephasing in thedemagnetization dynamics and observed that collective interactions can open a Dicke gap whichstabilizes a ferromagnetic state. At smaller interaction strength, the system demagnetizes but we showwe are able to coherently rephase the dynamics and restore magnetic order via many-body echoes. Thelong coherence times observed in weakly interacting Fermi gases can lead to surprisingly rich dynamicsthus offering great opportunities for advancing the frontiers of materials, quantum information andmetrology. A tribute to Debbie’s Legacy.

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The making of a polar molecule quantum gas

Jun Ye

JILA, NIST, University of Colorado

We have recently demonstrated that spin-orbit-coupled fermions can be engineered to occur naturally inan optical lattice clock. Precision spectroscopy of the clock transition now directly reveals how thesespin-orbit coupled fermions interact in the lattice.

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Universality and dynamics of impurities in quantum gases

Meera Parish

Monash University

The behaviour of a mobile impurity particle interacting with a quantum-mechanical medium is offundamental importance in physics. Ultracold atomic gases have greatly improved our understandingof the impurity problem owing to the high degree of control over experimental parameters such asinteractions and atom population. I will describe recent theoretical and experimental progress inexploring the properties of impurities (polarons) interacting with bosonic and fermonic mediums. Inparticular, I will discuss the universality of such polaron systems.

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Impurities strongly interacting with a Fermi sea

Rudolf Grimm

IQOQI Innsbruck, Austrian Academy of Sciences, Innsbruck, Austria

Impurities immersed in a Fermi sea show a wealth of exciting phenomena when their interaction with themedium is tuned via a Feshbach resonance. We report on experiments with small samples of fermionicor bosonic potassium atoms in a large, deeply degenerate Fermi sea of 6Li. In the case of fermionicimpurities (40K), we focus on the low-concentration limit and apply a Ramsey technique to study thefast response of the impurities to sudden changes of the interaction strength [1]. For near-resonantconditions, we observe the formation dynamics of quasiparticles (Fermi polarons) in real time and, inthe resonance case, an interference between the repulsive and the attractive quasiparticle branch. Forbosons (41K) in the Fermi sea, a small condensate is formed, which then acts as a mesoscopic impurity.For strongly repulsive conditions we find phase separation, such that the condensate resides in the centerof the Fermi sea and is strongly compressed by the fermionic environment. We show that three-bodyrecombination can serve as a probe for the spatial overlap at the interface between the two species. Thecomparison with a theoretical model reveals behavior beyond the local-density approximation. We alsostudy collective modes of the BEC in the Fermi gas across the transition to the phase-separated state,demonstrating dramatic frequency changes in particular for the radial breathing mode.

[1] M. Cetina, M. Jag, R. S. Lous, I. Fritsche, J. T. M. Walraven, R. Grimm, J. Levinsen, M. M. Parish, R. Schmidt, M. Knap, and E.

Demler, Science 354, 96 (2016).

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Experimental many-body physics using arrays of individual Rydberg atoms

Antoine Browaeys

Laboratoire Charles Fabry, Institut d’Optique, CNRS, 2 avenue A. Fresnel, 91127 Palaiseau, France

This talk will present our on-going effort to control the dipole-dipole interaction between cold Rydbergatoms in order to implement spin Hamiltonians that may be useful for quantum simulation of condensedmatter problems. In our experiment, we trap individual atoms in two-dimensional arrays of opticaltweezers [1] separated by few micrometers and excite them to Rydberg states using lasers. The arraysare produced by a spatial light modulator, which shapes the dipole trap beam. We can create almostarbitrary, two-dimensional geometries of the arrays with near unit filling [2].The talk will present our demonstration of the coherent energy exchange in small chains of Rydbergatoms resulting from their dipole-dipole interaction [3]. This exchange interaction realizes the XYspin model. We have also implemented the quantum Ising model [4]. The spin 1/2 Hamiltonian ismapped onto a system of Rydberg atoms excited by lasers and interacting by the van der Waals Rydberginteraction. We study various configurations such as one-dimensional chains of atoms with periodicboundary conditions, rings, or two-dimensional arrays containing up to 30 atoms. We measure thedynamics of the excitation for various strengths of the interactions between atoms. We compare thedata with numerical simulations of this many-body system and found excellent agreement for some ofthe configurations.This good control of an ensemble of interacting Rydberg atoms thus demonstrates a new promisingplatform for quantum simulation using neutral atoms, which is complementary to the other platformsbased on ions, magnetic atoms or dipolar molecules.

[1] Nogrette, Phys. Rev. X 4, 021034 (2014).

[2] Barredo, Science 354, 1021 (2016).

[3] Barredo, Phys. Rev. Lett. 114, 113002 (2015).

[4] Labuhn, Nature 534, 667 (2016).

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Latest results on dipolar phenomena in Erbium quantum gases

Francesca Ferlaino1,2

1 Institute of Experimental Physics University of Innsbruck2 Institute for Quantum Optics and Quantum Information (IQOQI) Austrian Academy of Sciences, Innsbruck Austria

This talk will present two sets of novel experimental results on dipolar quantum gases of highly-magneticErbium atoms. In a first experiment, we explore many-body dipolar phenomena in an Er BEC. Bycontrolling the ratio between the contact and dipole-dipole interaction (DDI) and the system geometry,we drive the system towards instability and observe a very rich dynamics. In the phonons regime,the dipolar BEC transforms into a macro-droplet state of high density, which survives well beyond themean-field collapse thanks to quantum fluctuations, in analogy to recent observation in Dy (Stuttgart).Differently, in the regime of short-wavelength excitation, we observe for the first time the populationof roton modes in the systems. The observed roton momentum exhibits its characteristic geometricaland interaction scaling. All our measurements are in remarkable agreement with parameter-free theorydescription.(∗) In a second set of experiments, we carry first investigations on spin physics in fermionic167Er. Due to its large quantum numbers, fermionic erbium realizes a high-spin system (Spin-19/2) with20 different states, interacting via both contact and DDI. The latter does not conserve magnetization,enriching the physics at play. In the experiment, we realize a spin mixture of degenerate fermions in athree-dimensional optical lattice and study the dynamics and scattering of the spin systems.(∗) Theory by L. Santos, R. M. W. van Bijnen, F. Waechtler

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Dipolar quantum gases and liquids

Tilman Pfau

Physikalisches Institut and Center for Integrated Quantum Science and Technology, Universität Stuttgart, Germany

The dipolar interaction is fundamentally different from the usual van der Waals forces in real gases.Besides the anisotropy, the dipolar interaction is nonlocal and as such allows for self-organized structureformation due to a roton instability similar to the Rosensweig instability in classical ferrofluids. In ourexperiments with quantum gases of Dysprosium atoms, we could observe the formation of a dropletcrystal initiated by a roton instability. In contrast to theoretical predictions based on a mean fieldapproach the superfluid droplets did not collapse. We confirmed experimentally that this unexpectedstability is due to beyond mean field quantum corrections of the Lee-Huang-Yang type. We also observeand study droplets that are self-bound in three dimensions, which can interfere with each other. Thesedroplets are 100 million times less dense than liquid helium droplets and open new perspectives as atruly isolated quantum system. Under strong confinement in one dimension, we observe the formationof a striped phase. In this situation a striped ground state is expected. We confirm experimentally thatthe mutual phases between the stripes is random, which confirms that for our current parameters theground state is not yet reached. We outline prospects to reach a phase coherent supersolid ground state.In a further ongoing experiment we rotate the droplets by a spinning magnetic field and observe thatthey can be rotated faster than the transverse trapping frequency. We observe a friction that damps theoscillation around a changing magnetization axis. Among other fascinating many-body phenomenastriped vortex lattices are within reach.

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Quantum thermalization dynamics with matrix-product states

Ehud Altman

University of California Berkeley

We study the dynamics of thermalization following a quantum quench using tensor-network methods.Contrary to the common belief that the rapid growth of entanglement and the resulting exponentialgrowth of the bond dimension restricts simulations to short times, we demonstrate that the long timelimit of local observables can be well captured using the time-dependent variational principle. This allowsto extract transport coefficients such as the energy diffusion constant from simulations with rather smallbond dimensions. We further study the characteristics of the quantum chaotic dynamics that precedesthe emergence of hydrodynamic flow. The chaotic wave obtained in our scheme travels ballisticallyin the system with a well defined “butterfly velocity”, but the wave-front broadens diffusively as itpropagates. I will discuss possible experimental schemes that may allow to measure these characteristicsof quantum chaos.

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Bose-Einstein condensates in imaginary potentials

Herwig Ott

Department of Physics, University of Kaiserslautern, Germany

Ultracold quantum gases are usually well isolated from the environment. This allows for the study ofground state properties and non-equilibrium dynamics of many-body quantum systems under almostideal conditions. Introducing a controlled coupling to the environment “opens” the quantum systemand non-unitary dynamics can be investigated. Such an approach provides new opportunities to studyfundamental quantum phenomena and to engineer robust many-body quantum states.I will present an experimental platform [1,2] that allows for the controlled engineering of dissipation inultracold quantum gases by means of localized particle losses. This is exploited to study quantum Zenodynamics in a Bose-Einstein condensate [3], where we find that the particle losses are well described byan imaginary potential in the system’s Hamiltonian. We also investigate the steady-states in a driven-dissipative Josephson array [4]. For small dissipation, the steady-states are characterized by balancedloss and gain and the eigenvalues are real. Above a critical dissipation strength, the system decaysexponentially, indicating the existence of purely imaginary eigenvalues, connected via an exceptionalpoint. I will discuss the implications to observe PT symmetric and PT broken phases in a many-bodyquantum system.

[1] T. Gericke et al., Nature Physics 4, 949 (2008).

[2] P. Würtz et al., Phys. Rev. Lett. 103, 080404 (2009).

[3] G. Barontini et al., Phys. Rev. Lett. 110, 035302 (2013).

[4] R. Labouvie et al., Phys. Rev. Lett. 116, 235302 (2016).

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A cold-atom Fermi-Hubbard antiferromagnet

Markus Greiner

Harvard University, Cambridge, USA

We report on the realization of antiferromagnets in a cold-atom 2D Fermi-Hubbard system. We observelong-range antiferromagnetic order and access the doped regime of the Fermi-Hubbard phase diagram.In this regime computations become exponentially difficult, and pseudogap physics and, for lowertemperatures, high-Tc superconducting states are expected to emerge. The unprecedented level ofcontrol afforded by quantum gas microscopy enables us to engineer low entropy states, and to directlymeasure the propagation of excitations, illuminating the intricate interplay between spin and motionaldegrees of freedom in the Fermi-Hubbard system.

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Exploring quantum magnetism at the single spin and atom level

Christian Gross

Max Planck Institute

Quantum gas microscopes enable the single spin resolved observation and manipulation of ultracoldatoms in optical lattices. This powerful tool provides access to novel observables for the characterizationof tailored many-body systems. We report on progress on the study of one dimensional ultracold Fermionsin an optical lattice, for which we recently observed antiferromagnetic correlations at half filling andpersisting strong string correlations in the doped regime. The string correlations experimentally revealthat magnetic correlations in Hubbard chains are not absent but merely hidden by the holes or doublons.This is a striking signature of spin-charge separation which, given the non-local observables provided byquantum gas microscopes, can now be detected even in equilibrium situations.

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Strongly correlated Fermi gases under the microscope

Martin Zwierlein

Massachusetts Institute of Technology

Strong electron correlations lie at the origin of transformative phenomena such as colossal magneto-resistance and high-temperature superconductivity. Already near room temperature, doped copper oxidematerials display remarkable features such as a pseudo-gap and a “strange metal” phase with unusualtransport properties. The essence of this physics is believed to be captured by the Fermi-Hubbard modelof repulsively interacting, itinerant fermions on a lattice. I will describe our recent experiments on two-dimensional Fermi gases of 40K atoms under a Fermi gas microscope [1], where metallic, Mott insulatingand band insulating states of the Fermi-Hubbard model were observed with single-site, single-atomresolution [2]. The microscope allows for the site-resolved observation of charge and spin correlationsin this system [3]. It directly reveals anti-ferromagnetic spin correlations, the Pauli and correlation holein the metallic regions, and strong doublon-hole bunching in the region near half-filling. The latter isexpected in the presence of singlet bonds forming between adjacent lattice sites and should play animportant role for transport in the Fermi-Hubbard model.

[1] Lawrence W. Cheuk, Matthew A. Nichols, Melih Okan, Thomas Gersdorf, Vinay V. Ramasesh, Waseem S. Bakr, Thomas Lompe,

and Martin W. Zwierlein, Phys. Rev. Lett. 114, 193001 (2015).

[2] Lawrence W. Cheuk, Matthew A. Nichols, Katherine R. Lawrence, Melih Okan, Hao Zhang, and Martin W. Zwierlein, Phys. Rev.

Lett. 116, 235301 (2016).

[3] Lawrence W. Cheuk, Matthew A. Nichols, Katherine R. Lawrence, Melih Okan, Hao Zhang, Ehsan Khatami, Nandini Trivedi,

Thereza Paiva, Marcos Rigol, and Martin W. Zwierlein, Science 353, 1260 (2016).

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Bose-Fermi dual superfluids

Christophe Salomon, Sebastien Laurent, Matthieu Pierce, Marion Delehaye, Shuwei Jin, Tarik Yefsah,Igor Ferrier-Barbut, and Frederic Chevy

Ecole Normale Supérieure, Laboratoire Kastler Brossel

We will report on the production and study of a mixture of Bose and Fermi superfluids. Such a mixturehas long been sought in liquid helium where superfluidity was achieved separately in bosonic 4He andfermionic 3He. However due to strong interactions between isotopes, phase separation occurs whenthe 3He concentration exceeds 6%, which, so far, has prevented reaching simultaneous superfluidityfor both species. Using dilute quantum gases where interactions can be tuned, we have produced aBose-Fermi mixture where both species are superfluid [1]. By exciting center of mass oscillations of themixture we probe the collective dynamics of the system. Coherent energy exchange between the Boseand Fermi gas is observed with very small damping below a certain critical velocity. We compare thiscritical velocity for superfluid counterflow to a recent theoretical prediction [2,3]. Finally raising thetemperature of the system slightly above the superfluid transition reveals an unexpected phase-lockingof the oscillations induced by dissipation.

[1] Igor Ferrier-Barbut, Marion Delehaye, Sebastien Laurent, Andrew T. Grier, Matthieu Pierce, Benno S. Rem, Frédéric Chevy, and

Christophe Salomon, A mixture of Bose and Fermi superfluids, Science 345, 1035, (2014).

[2] Y. Castin, I. Ferrier-Barbut, and C. Salomon, The Landau critical velocity for a particle in a Fermi superfluid, Comptes Rendus

Physique 16, 241 (2015).

[3] M. Delehaye, S. Laurent, I. Ferrier-Barbut, S. Jin, F. Chevy, and C. Salomon, Critical velocity and dissipation of an ultracold

Bose-Fermi counterflow, Phys. Rev. Lett. 115, 265303 (2015).

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Excitations and non-equilibrium physics of strongly interacting Fermi gases

Michael Koehl

University of Bonn

Quantum gases are particularly promising systems to study quantum dynamics owing to long coherencetimes and slow relaxation. In the talk we will discuss our recent experiments of the dynamics of stronglyinteracting Fermi gases following rapid quenches and periodic modulations.

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Exciton-polariton condensation in non-Hermitian potentials

Elena Ostrovskaya

Nonlinear Physics Centre, Research School of Physics & Engineering, The Australian National University, Canberra, ACT 2601

Australia

Exciton polaritons are hybrid light-matter bosons formed by strongly interacting photons and excitonsin semiconductor microcavities. Sufficiently strong optical pumping can drive exciton polaritons tonon-equilibrium Bose-Einstein condensation. At the same time, an optical pump creates a local potentialbarrier for exciton polaritons due to the energy shifts induced by interaction between polaritons and athermal reservoir. This feature can be employed to create reconfigurable pumpinduced traps for thepolariton condensate. Optically-induced trapping potentials are intrinsically non-Hermitian, and precisecontrol over their real and imaginary parts offers an opportunity to explore non-Hermitian quantumphysics with exciton polaritons. In this talk, we will review main properties of the exciton-polaritoncondensation in non-Hermitian potentials and discuss our related observations of exceptional points,polariton flows with controlled chirality (handedness), and nontrivial whispering gallery states.

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Cavity polariton lattices: A non-linear photonic emulator

Jacqueline Bloch

Centre de Nanosciences et de Nanotechnologies (C2N) CNRS, Univ. Paris-Sud, Université Paris-Saclay

Semiconductor microcavities appear today as a new platform for the study of quantum fluids of light.They enable confining both light and electronic excitations (excitons) in very small volumes. Theresulting strong light-matter coupling gives rise to hybrid light-matter quasi-particles named cavitypolaritons. Polaritons propagate like photons but strongly interact with their environment via theirmatter part: they are fluids of light and show fascinating properties such as superfluidity or nucleationof quantized vortices. Sculpting microcavities at the micron scale, we fabricate at C2N lattices of variousgeometries and use this photonic platform for the emulation of different Hamiltonians. After a generalintroduction, I will illustrate the potential of this photonic plateform describing two recent experiments.1) We could image edge states in a 1D Fibonacci polariton quasi-crystal and measure their windingnumber associated to topological invariants, when varying a structural parameter named phason [1]. 2)We implemented an SSH topological chain and could demonstrate lasing on a topological edge states.Because of the topological origin of this mode, the lasing mode presents strong robustness againstperturbation [2]. These works open a lot of perspectives related to 2D lattices and making use of thestrong polariton Kerr non-linearity.

[1] F. Baboux et al., Measuring topological invariants from generalized edge states in polaritonic quasicrystals, Phys. Rev. B 95,

161114(R) (2017).

[2] P. St-Jean et al., Lasing in topological edge states of a 1D lattice, under review (arXiv:1704.07310).

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Photons and atoms in synthetic magnetic fields and synthetic dimensions

Iacopo Carusotto

INO-CNR BEC Center and Dipartimento di Fisica, Universitá di Trento

In this talk I will review the recent advances in the theoretical and experimental study of quantummagnetic effects in optical and atomic systems in the presence of strong synthetic gauge fields. In thefirst part, I will illustrate the consequences of a non-trivial topology on the properties of the edge andof the bulk of the system and I will offer a novel point of view on single-particle quantum dynamicsin terms of the Berry phase as a momentum space magnetic field. In the second part, I will show howsynthetic dimensions can be engineered in both atomic and photonic systems. The advantages anddisadvantages of either platform in view of high-dimensional many-body physics will be specificallydiscussed. I will conclude by outlining the exciting perspectives opened by the recent advances in thestudy of strongly correlated fluids of light in different configurations.

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Dissipative and coherent dynamics in a Josephson junction between fermionicsuperfluids

Giacomo Roati1,2

1 CNR-INO, via N. Carrara 1, Sesto Fiorentino, Italy2 LENS, University of Florence, via N. Carrara 1, Sesto Fiorentino, Italy

I will report on the emergence of dissipation in an atomic Josephson junction between two weakly-coupled superfluid Fermi gases [1]. In the experiment, we create the analogous of a Josephson junctionby bisecting BEC-BCS crossover superfluids with a thin optical barrier [2]. For all the interactionsregimes, we find that vortex-induced phase slippage is the dominant microscopic source of dissipation.For intermediate bias potentials, the dynamics exhibits coexisting coherent oscillations and resistive flow.We link the junction transport properties to the phase-slippage mechanism, finding that vortex nucleationis primarily responsible for the observed trends of conductance and critical current. We also enter theregime of strong dissipation when the junction operation is irreversibly affected by vortex proliferation,causing the loss of coherence between the superfluid reservoirs. Our work opens new directions forinvestigating the interplay between dissipative and superfluid transport in strongly-correlated fermionicsystems.

[1] A. Burchianti, F. Scazza, A. Amico, G. Valtolina, J. A. Seman, C. Fort, M. Zaccanti, M. Inguscio, and G. Roati, arXiv:1707.02784v1

(2017).

[2] G. Valtolina, A. Burchianti, A. Amico, E. Neri, K. Xhani, J. A. Seman, A. Trombettoni, A. Smerzi, M. Zaccanti, M. Inguscio, and

G. Roati, Science 350, 1505 (2015).

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Two rigorous results on dynamics of quantum systems

Hui Zhai

Tsinghua University

In this talk I will present two rigorous results on dynamics of quantum systems. These two theorems arenot only mathematically rigorous, but also are universal and directly related to current experiments.The first theorem is related to symmetry. We show that the symmetry of single particle Hamiltoniancan impose a strong constraint on the interaction effect on dynamics, that is, the time dependentdynamics of certain observables are symmetric with respect to repulsive and attractive interactions. Thistheorem can unify three seemingly disparate experiments from Munich and Harvard groups. The secondtheorem is related to topology. Considering the quench dynamics of a two-band Chern insulator from atopological trivial state, we show the Chern number of the final Hamiltonian can be read out from thequench dynamics through the linking number. This predication can also be directly verified in availableexperimental settings.

[1] J. Yu, N. Sun, and H. Zhai, arXiv:1708.08070 (2017).

[2] C. Wang, P. Zhang, X. Chen, J. Yu, and H. Zhai, Phys. Rev. Lett. 118, 185701 (2017).

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EPR and spatial-mode entanglement in spinor Bose-Einstein condensates

Ilka Kruse,1 Jan Peise,1 Karsten Lange,1 Bernd Lücke,1 Luca Pezzè,2 Giuseppe Vitagliano,3 IagobaApellaniz,3 Matthias Kleinmann,3 Jan Arlt,4 Wolfgang Ertmer,1 Klemens Hammerer,5 Géza Tóth,3 Luis

Santos,5 Augusto Smerzi,2 and Carsten Klempt1

1 Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany2 Istituto Nazionale di Ottica, INO-CNR, Largo Enrico Fermi 2, 50125 Firenze, Italy

3 Department of Theoretical Physics, University of the Basque Country UPV/EHU, PO Box 644, E-48080 Bilbao, Spain4 Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade 120, DK-8000 Århus C, Denmark

5 Institut für Theoretische Physik, Leibniz Universität Hannover, AppelstraÃ§e 2, D-30167 Hannover, Germany

Spin changing collisions in alkaline Bose-Einstein condensates can be employed to generate highlyentangled atomic quantum states. Here, we will report on the generation of two classes of entangledstates. Firstly, we demonstrate the generation of two-mode squeezed vacuum states and record theircharacteristic quadrature correlations by atomic homodyning. We prove that the correlations fulfillReid’s criterion [1] for continuous-variable Einstein-Podolsky-Rosen entanglement. The homodynemeasurements allow for a full tomographic reconstruction, yielding a two-mode squeezed state with a78% fidelity. The created state can be directly applied to atom interferometry, as is exemplified by anatomic clock measurement beyond the Standard Quantum Limit.Secondly, we demonstrate entanglement between two spatially separated atomic modes. The entangledstate is obtained by spatially splitting a Twin Fock state of indistinguishable atoms. The method opens apath to exploit the recent success in the creation of many-particle entanglement in ultracold atoms forthe field of quantum information, where individually addressable subsystems are required. Finally, wewill show how the measurement protocol can be extended to perform a Bell test of quantum nonlocality.

[1] M. Reid, Phys. Rev. A 40, 913 (1989).

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Detecting the nonlocality of many-body quantum states

Maciej Lewenstein

ICFO – Institut de Ciencies Fotoniques and The Barcelona Institute of Science and Technology

One of the most important steps in the understanding of quantum many-body systems is due to theintensive studies of their entanglement properties [1,2]. Much less, however, is known about the roleof quantum nonlocality [3] in these systems. This is because standard many body observables involvecorrelations among few particles, while there is no multipartite Bell inequality for this scenario.In the introduction I will discuss shortly the role of entanglement in many body systems, stressing thedifference between the gapped and critical systems. I will then concentrate on the results of Refs. [4],where we provide the first examples of nonlocality detection in many-body systems using two-bodycorrelations. To this aim, we construct families of multipartite Bell inequalities that involve only secondorder correlations of local observables. We then provide examples of systems, relevant for nuclear andatomic physics, whose ground states violate our Bell inequalities for any number of constituents. Weidentify inequalities that can be tested by measuring collective spin components, opening the way to theexperimental detection of many-body nonlocality, for instance with atomic ensembles [5], systems oftrapped ions [6], or atoms trapped close to nano-structured (tapered) fibers and photonic crystals [7].Interestingly, breaking of many body Bell inequalities witnesses certain kinds of many body entanglement[8]. Most of examples will deal with symmetric states, i.e. will call for metrological applications [9]. Iftime permits, we discuss non-locality in 1D spin-chains, by employing Jordan-Wigner transformationand relation to integrable and non-integrable fermionic models [10].

[1] A. Osterloh et al., Nature 416, 608 (2002); T. J. Osborne et al., Quantum Inf. Proc. 1, 45 (2002); Phys. Rev. A 66, 032110

(2002); G. Vidal et al., Phys. Rev. Lett. 90, 227902 (2003).

[2]M. Lewenstein, A. Sanpera, and V. Ahufinger, Ultracold atoms in optical lattices: Simulating quantum many body physics, (Oxford

University Press, Oxford, 2017), ISBN 978-0-19-878580-4.

[3] J. S. Bell, Physics 1, 195 (1964).

[4] J. Tura et al., Detecting the non-locality of quantum many body states, Science 344, 1256 (2014); J. Tura et al., Nonlocality in

many-body quantum systems detected with two-body correlators, Ann. Phys. 362, 370 (2015).

[5] K. Hammerer et al., Rev. Mod. Phys. 82, 1041 (2010); K. Eckert et al., Nature Phys. 4, 50 (2008).

[6] T. Graß and M. Lewenstein, Trapped-ion quantum simulation of tunable-range Heisenberg chains, arXiv:1401.6414, EPJ Quantum

Technology 2014, 1:8, doi:10.1186/epjqt8.

[7] J. S. Douglas, H. Habibian, C.-L. Hung, A. V. Gorshkov, H. J. Kimble, and D. E. Chang, Quantum many-body models with cold

atoms coupled to photonic crystals, Nature Photon. 9, 326 (2015).

[8] A. Aloy et al., Device independent entanglement depth witnesses, in preparation.

[9] M. Oszmaniec, R. Augusiak, C. Gogolin, J. Kolodynski, A. Acín, and M. Lewenstein, Random bosonic states for robust quantum

metrology, Phys. Rev. X 6, 041044 (2016).

[10] J. Tura, G. de las Cuevas, R. Augusiak, M. Lewenstein, A. Acín, and J. I. Cirac, Energy as a detector of nonlocality of many-body

spin systems, Phys. Rev. X 7, 021005 (2017).

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Atomic spin entanglement and anyonic fractional statistics in a spin-dependentoptical superlattice

Zhen-Sheng Yuan and Jian-Wei Pan

University of Science an Technology of China

In this talk, I will report our recent research progress with ultracold atoms trapped in optical lattices.Ultracold atoms in optical lattices hold promise for the creation of entangled states for quantumsimulation and quantum computation. In our experiment, we developed a novel setup of spin-dependentoptical superlattice. We were able to generate, manipulate and detect the atomic spin entanglementin this lattice [1]. It is an important progress towards creating scalable entangled states for quantuminformation processing [2]. Moreover, based on the techniques of precisely manipulating atomic spins,we built a minimum version of the toric code Hamiltonian with four atomic spins in optical plaquettes.We observed four-body ring-exchange interactions, existing in many-body systems while never observedbefore in experiment, and the topological properties of anyonic excitations within this ultracold atomsystem [3]. This work represents an essential step towards studying topological matters with ultracoldatoms and offers new perspectives on topological quantum simulation [4-6].

[1] H. -N. Dai, B. Yang, A. Reingruber, X.-F. Xu, X. Jiang, Y.-A. Chen, Z.-S. Yuan, and J.-W. Pan, Generation and detection of atomic

spin entanglement in optical lattices, Nature Physics 12, 783 (2016).

[2] B. Vaucher, A. Nunnenkamp, D. Jaksch, Creation of resilient entangled states and a resource for measurement-based quantum

computation with optical superlattices, New J. Phys. 10, 023005 (2008).

[3] H.-N. Dai, B. Yang, A. Reingruber, H. Sun, X.-F. Xu, Y.-A. Chen, Z.-S. Yuan, and J.-W. Pan, Observation of four-body ring-exchange

interactions and anyonic fractional statistics, arXiv:1602.05709 (To appear, Nature Physics).

[4] A. Y. Kitaev, Fault-tolerant quantum computation by anyons, Ann. Phys. 303, 2 (2003).

[5] B. Paredes and I. Bloch, Minimum instances of topological matter in an optical plaquette, Phys. Rev. A 77, 023603 (2008).

[6] H. Büchler, M. Hermele, S. Huber, M. P. Fisher, and P. Zoller, Atomic quantum simulator for lattice gauge theories and ring

exchange models, Phys. Rev. Lett. 95, 040402 (2005).

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Studying superfluidity with ultracold atom circuits

Gretchen Campbell

Joint Quantum Institute, NIST and UMD

Ultracold atomic gases are an ideal system for studying superfluid behavior. By manipulating opticalpotentials, we are able to create ring-shaped Bose-Einstein condensates. We have used this “atom circuit”to create and study long-lived persistent currents. The currents are controlled with an additional laserbeam, which acts as a barrier, or “weak link” across one side of the ring. By tuning the properties of ourweak link we are able to drive transitions between persistent current states, and we have studied how thecritical velocity for the transitions is affected by the strength of the perturbation and the temperature ofthe system. In a recent experiment, we’ve also studied the behavior of the ring-shaped condensate whenit is supersonically expanded. The standard cosmological picture involves a universe that is expanding,sometimes many orders of magnitude faster than the speed of light. This expansion impacts the quantumfields that exist inside our universe. By expanding our ring we’ve created a system that realizes the basicfeatures of this expansion. Specifically, we’ve demonstrated redshifting of phonons and a reheating effectthat is similar to pre-heating after the inflation stage of the universe. We also observe that spontaneousnon-zero winding numbers appear in the ring after the expansion is complete. These experiments mayopen up the possibility of exploring interesting cosmological physics in Bose-Einstein condensates andother quantum systems.

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Strongly interacting bosons

Zoran Hadzibabic

University of Cambridge

I will discuss our recent experiments on strongly interacting Bose gases, (usually) produced in homoge-neous optical box traps. These include the observation of the three-body contact in the unitary thermalBose gas [1], measurements of the excitation energy and quantum depletion in a homogeneous stronglyinteracting BEC [2,3], and observation of the universal scaling laws in the dynamics of a degeneratehomogeneous gas quenched to unitarity [4].

[1] R. J. Fletcher et al., Science 355, 377 (2017).

[2] R. Lopes et al., PRL 118, 210401 (2017).

[3] R. Lopes et al., arXiv:1706.01867 (2017).

[4] C. Eigen et al., in preparation.

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Microscopy of atomic Fermi-Hubbard systems in new regimes

Waseem Bakr

Princeton University

The ability to probe and manipulate ultracold fermions in optical lattices at the atomic level usingquantum gas microscopes has enabled quantitative studies of Fermi-Hubbard models in a temperatureregime that is challenging for state-of-the-art numerical simulations. Experiments have focused onspin-balanced gases of repulsively interacting atoms with the hope of elucidating phenomena in thehigh-temperature superconductors. In this talk, I will present experiments that explore the Hubbardmodel in two new regimes: repulsive gases with spin-imbalance and attractive spin-balanced gases.In the first regime, we observe canted antiferromagnetism at half-filling, with stronger correlationsin the direction orthogonal to the magnetization. Away from half-filling, the polarization of the gasexhibits non-monotonic behavior with doping, resembling the behavior of the magnetic susceptibility ofthe cuprates. The attractive Hubbard model studied in the second set of experiments is the simplesttheoretical model for studying pairing and superconductivity of fermions in a lattice. Our measurementson the normal state reveal checkerboard charge-density wave correlations close to half-filling. Thecharge-density-wave correlations are a sensitive thermometer in the low temperature regime relevantfor future studies of inhomogeneous superfluid phases in spin-imbalanced attractive gases.

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Probing many-body dynamics on a 51-atom quantum simulator

Hannes Bernien

Harvard University

Controllable, coherent many-body systems provide unique insights into fundamental properties ofquantum matter, allow for the realization of novel quantum phases, and may ultimately lead to compu-tational systems that are exponentially superior to existing classical approaches. Here, we demonstratea novel platform for the creation of controlled many-body quantum matter. Our approach makes use ofdeterministically prepared, reconfigurable arrays of individually controlled, cold atoms. Strong, coherentinteractions are enabled by coupling to atomic Rydberg states. We realize a programmable Ising-typequantum spin model with tunable interactions and system sizes of up to 51 qubits. Within this model weobserve transitions into ordered states (Rydberg crystals) that break various discrete symmetries, verifyhigh-fidelity preparation of ordered states, and investigate dynamics across the phase transition in largearrays of atoms. In particular, we observe a novel type of robust many-body dynamics corresponding topersistent oscillations of crystalline order after a sudden quantum quench.

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Negative-mass quantum hydrodynamics with spin-orbit coupled BECs

Peter Engels

Washington State University

In recent years, spin-orbit coupled BECs have become a major focus of research for the investigation ofquantum dynamics. Spin-orbit coupling can be induced in a BEC by Raman dressing techniques and isassociated with artificial gauge fields and roton-like minima in the dispersion relation. Here we presentexperimental studies of quantum hydrodynamical effects connected to the peculiar dispersion relationof a spin-orbit coupled BEC. For example, under appropriate conditions the dispersion can feature aregion of negative curvature, which implies a negative effective mass of the atoms. In our experimentswe observe negative mass effects by probing the response of a BEC to an applied force. The currentstatus of the BEC research at Washington State University will be discussed.

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Bell correlations in a Bose-Einstein condensate

Roman Schmied,1 Jean-Daniel Bancal,1,2 Baptiste Allard,1 Matteo Fadel,1 Valerio Scarani,2 NicolasSangouard,1 and Philipp Treutlein1

1 University of Basel, Switzerland2 National University of Singapore

The parts of a composite system can share correlations that are stronger than any classical theoryallows. These so-called Bell correlations can be confirmed by violating a Bell inequality and representthe most profound departure of quantum from classical physics. We report experiments where wedetect Bell correlations between the spins of 480 atoms in a Bose-Einstein condensate [1]. We derive aBell correlation witness from a recent many-particle Bell inequality [2] involving one- and two-bodycorrelation functions only. Our measurement on a spin-squeezed state exceeds the threshold for Bellcorrelations by 3.8 standard deviations. Concluding the presence of Bell correlations is unprecedentedfor an ensemble containing more than a few particles. Our work shows that the strongest possiblenon-classical correlations are experimentally accessible in many-body systems, and that they can berevealed by collective measurements. This opens new perspectives for using many-body systems inquantum information tasks.

[1] R. Schmied, J. D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein, and N. Sangouard, Science 352, 441 (2016).

[2] J. Tura, R. Augusiak, A. B. Sainz, T. Vertesi, M. Lewenstein, and A. Acin, Science 344, 1256 (2014).

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Thermalized light in variable micropotentials and coupled photon condensates

Julian Schmitt,1 David Dung,1 Christian Kurtscheid,1 Tobias Damm,1 Frank Vewinger,1 Jan Klaers,1,2

and Martin Weitz1

1 Institut für Angewandte Physik, Universität Bonn2 Institute for Quantum Electronics, ETH Zurich

Cold atoms in lattice potentials are an attractive platform to simulate phenomena known from solidstate theory, as the Mott-insulator transition. In contrast, the field of photonics usually deals withnonequilibrium physics. Recent advances towards photonic equilibrium physics include polariton latticeexperiments, as well as the demonstration of a photon condensate in a dye-filled microcavity [1-3].Here we report the creation of variable micropotentials for light using thermo-optic imprinting withina high-finesse microcavity filled with a dye-polymer solution. Using an auxiliary laser beam, spatiallytransverse variations of the refractive index in the cavity were employed by local temperature increaseof the dye-polymer solution, which allows us to tailor variable potentials for the microcavity photons.Within the generated trapping potentials, photons by repeated absorption-emission cycles thermalizeto the temperature of the dye solution, and in a single microsite we observe a photon Bose-Einsteinmicrocondensate. Effective interactions between the otherwise nearly non-interacting photons areobserved due to thermo-optic effects, and in a double-well system tunnel coupling between sites isdemonstrated, as well as the hybridization of eigenstates. Prospects of the findings include photoniclattices in which cooling alone can produce entangled many-body states.

[1] See, e.g: N. Proukakis et al., Bose-Einstein condensation (eds.), (Cambridge, in press).

[2] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010).

[3] T. Damm et al., Nature Commun. 7, 11340 (2016).

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A single atom probe of lattice gases in momentum space

H. Cayla,1 C. Carcy,1 Q. Bouton,1 R. Chang,1 M. Mancini,1 D. Clément,1 and G. Carleo2

1 Laboratoire Charles Fabry, Institut d’Optique, CNRS, Univ. Paris Saclay2 Institute for Theoretical Physics, ETH Zurich

Correlations between the degrees of freedom of individual quantum particles has been identified as a keyressource to solve open many-body problems. So far, a large experimental effort has been devoted to thebuilding of apparatus capable of measuring spatial and spin correlations in one and two dimensions. Wewill present an experiment that provides access to multi-particle correlations between the momentumdegree of freedom in three-dimensional lattice systems. We produce Bose-Einstein condensates ofHelium-4 atoms in a metastable state [1, 2], whose internal energy (19.6 eV) is large enough to allowfor an electronic detection of individual atoms in three dimensions [3, 4]. When released from a 3Doptical lattice, we probe the gas in the far-field regime of expansion where the atom distribution canbe exactly mapped on the in-trap momentum distribution. Comparison with ab-initio Quantum-MonteCarlo calculations in the Bose-Hubbard regime qualifies our apparatus as a single-atom probe deliveringmomentum distributions of strongly interacting systems as large as 60× 60× 60 sites. We also illustratenovel capabilities to access physical quantities of interest, like the condensed fraction, by investigatingthe superfluid-to-normal phase transition.

[1] Q. Bouton, R. Chang, L. Hoendervanger, F. Nogrette, A. Aspect, C. I. Westbrook, and D. Clément, Phys. Rev. A 91, 061402(R)

(2015).

[2] R. Chang, Q. Bouton, H. Cayla, C. Qu, A. Aspect, C. I. Westbrook, and D. Clément, Phys. Rev. Lett. 117, 235303 (2016).

[3] M. Schellekens, R. Hoppeler, A. Perrin, J. Viana Gomes, D. Boiron, A. Aspect, and C. I. Westbrook, Science 310, 648 (2005).

[4] F. Nogrette, D. Heurteau, R. Chang, Q. Bouton, C. I. Westbrook, R. Sellem, and D. Clément, Rev. Scient. Intrum. 86, 113105

(2015).

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A photon-photon quantum gate based on Rydberg polaritons

Stephan Dürr

MPI for Quantum Optics

Rydberg polaritons offer a unique way to create strong interactions for photons. We utilize theseinteractions to demonstrate a photon-photon quantum gate. To achieve this, a photonic control qubitis stored in a quantum memory consisting of a superposition of a ground state and a Rydberg state inan ultracold atomic gas. This qubit interacts with a photonic target qubit in the form of a propagatingRydberg polariton to generate a conditional pi phase shift, as in Ref. [1]. Finally, the control photon isretrieved. We measure two controlled-NOT truth tables and the two-photon state after an entangling-gate operation. This work is an important step toward applications in optical quantum informationprocessing, such as deterministic photonic Bell-state detection which is crucial for quantum repeaters.

[1] D. Tiarks et al., Science Advances 2, 1600036 (2016).

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Observation of quantum Hawking radiation and its entanglement in ananalogue black hole

Jeff Steinhauer

Technion

We observe spontaneous Hawking radiation, stimulated by quantum vacuum fluctuations, emanatingfrom an analogue black hole in an atomic Bose-Einstein condensate. The Hawking radiation is observedvia the correlations between the Hawking radiation exiting the black hole and the partner particles fallinginto the black hole. The quantum nature of the Hawking radiation is observed through entanglement.The experiment is seen to be well within the quantum regime, since the measured Hawking temperatureis far below the upper limit for quantum entanglement. A broad energy spectrum of entangled Hawkingpairs are observed. Maximal entanglement is observed for the high energy part of the Hawking spectrum,while the lowest energies are not entangled. Thermal behavior is seen at very low and high energies.Further insight is obtained by a preliminary experiment in which the horizon is caused to oscillate at afixed frequency, which stimulates waves travelling into and out of the black hole. The rate of particleproduction and the dispersion relation measured in the preliminary experiment are consistent with theHawking radiation experiment. Additional confirmation of the results is obtained through a numericalsimulation, which demonstrates that the Hawking radiation occurs in an approximately stationarybackground. The measurement reported here verifies Hawking’s calculation, which is viewed as amilestone in the quest for quantum gravity. The observation of Hawking radiation and its entanglementverifies important elements in the discussion of information loss in a real black hole.

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Scrambling quantum information in cold atoms with light

Monika Schleier-Smith

Stanford University

When a qubit falls into a black hole, the information is rapidly “scrambled”, i.e., entangled with the blackhole’s many internal degrees of freedom. Scrambling is a manifestation of many-body quantum chaos,suggesting that strongly interacting quantum systems realizable in the laboratory might offer a route totable-top simulations of quantum gravity. Conducive to fast scrambling are non-local interactions. I willdescribe prospects for implementing chaotic non-local spin models with cold atoms strongly coupled tophotons in an optical resonator. Numerical simulations indicate fertile ground for explorations rangingfrom collective spin dynamics compatible with semi-classical intuitions to inherently many-body chaos.

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Creating materials from light: Landau levels, Mott insulators, and Laughlinpuddles

Jonathan Simon


In this talk I will discuss ongoing efforts in my group exploring topological- and strongly-interacting-phases of light. I will begin with our observation of photonic Landau levels in curved space, createdby trapping light in twisted (non-planar) optical cavities, and culminating in the first measurement ofthe mean orbital spin of integer Hall state, a normally-inaccessible topological quantum number. I willthen discuss our recent demonstration of colliding cavity Rydberg polaritons, plus ongoing efforts toload the polaritons into a twisted cavity to create Laughlin states. I will conclude by summarizing acollaboration with the Schuster lab where we have recently created both a photonic Chern insulator anda dissipatively stabilized photonic Mott insulator.

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Excitation spectra of near-homogeneous Fermi gases

Chris Vale

Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia

We present measurements of the excitation spectra of strongly interacting Fermi gases at both low andhigh momentum using focused beam Bragg spectroscopy. At low momentum, below the superfluidtransition temperature, the Goldstone mode or Bogoliubov-Anderson phonon is the dominant lowenergy excitation. For energies larger than twice the pairing gap, the single-particle continuum becomesvisible. The frequencies of the phonon mode and the onset of single-particle excitations provide directmeasures of the speed of sound and pairing gap, respectively. At high momentum, focused beam Braggspectroscopy allows the determination of Tan’s universal contact parameter and the internal energy viathe application of sum-rules. These allow us to map the temperature dependence of the contact andenergy for gases at unitarity.

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1D–3D crossover of a spin-imbalanced Fermi gas

Randall Hulet

Rice University

The issue of pairing of magnetized, or “spin-imbalanced” Fermi gases has been an open question inquantum many body physics for more than 50 years. It is still not known whether a material cansimultaneously exhibit superconducting and magnetic order as embodied by the FFLO state, althoughthe answer to this question has implications for fields as diverse as unconventional superconductivity tothe equation of state of neutron stars.I will review our experimental investigations of the phases of spin-imbalanced atomic quantum gases in1D [1], 3D [2], and in the crossover regime between 1D and 3D [3]. The FFLO state has not been seenin 3D, and theory is ambiguous in this case. FFLO is pervasive in the T = 0 phase diagram in 1D, butit may be unstable at experimentally achievable temperatures. The 1D–3D crossover, experimentallyrealized by a 2D optical lattice in which the quasi-1D tubes are weakly coupled to nearest neighbors,may be the optimum place to detect FFLO. The crossover is readily observable by in situ imaging ofthe density because phase separation between an unpolarized superfluid phase and polarized phases isinverted in a 1D trap compared with 3D. Progress on the direct detection of FFLO in this region will bereported.

[1] Y. A. Liao et al., Nature 467, 567 (2010).

[2] B. A. Olsen et al., Phys. Rev. A 92, 063616 (2015).

[3] M. C. Revelle et al., Phys. Rev. Lett. 117, 235301 (2016).

65

ABSTRACTSof the

poster presentations


Poster-1-1 « Back to program

High-efficient adiabatic transport of a Bose-Einstein condensate in coupled wellpotentials

Juan Luis Rubio,1 Jordi Mompart,1 Thomas Busch,2 and Veronica Ahufinger1

1 Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra, Spain2 Quantum Systems Unit, OIST Graduate University, Onna, Okinawa 904-0495, Japan

Spatial adiabatic passage (SAP) [1] has been proposed for high fidelity and robust transport of quantumparticles between the outermost traps of a triple-well potential by adiabatically following an energyeigenstate, the so-called spatial dark state, of the system. Nevertheless, for Bose-Einstein condensates(BEC), the on-site interaction breaks the resonance condition between the two outermost wells, and levelcrossings can appear during the dynamics preventing the adiabatic following of the energy eigenstate.We investigate SAP of a BEC in a triple well potential within the three-mode approximation for arbitraryvalues of the non-linearity and the energy bias between the wells [2]. By rewriting the dynamics in theso-called time-dependent dark/dressed basis, we analytically derive the optimal conditions for a highlyefficient transport. In particular, we show that the non-linearity relaxes the requirement of degeneracybetween the on-site energies of the initial and target wells giving rise to a plateau in the transportefficiency as a function of the energy bias between these two wells. The width of this plateau can beincreased by an appropriate local modification of the non-linearity.

[1] R. Menchon-Enrich et al., Rep. Prog. Phys. 79, 074401 (2016).

[2] J. L. Rubio et al., Phys. Rev. A 94, 053606 (2016).

69



Fragmented supersolid of dipolar excitons

Sergey Andreev

LOMA, University of Bordeaux

We discuss a possible link between the recently observed macroscopic ordering of ultra cold dipolarexcitons (MOES) and the phenomenon of supersolidity. In the dilute limit we predict a stable supersolidstate for a quasi-one-dimensional system of bosonic dipoles characterized by two- and three-body contactrepulsion. We phenomenologically extend our theory to the strongly-correlated regime and find a criticalvalue of the contact interaction parameter at which the supersolid exhibits a quantum phase transitionto a fragmented state. The wavelength of the fragmented supersolid is defined by the balance betweenthe quantum pressure and the entropy due to fluctuations of the relative phases between the fragments.Our model appears to be in good agreement with the relevant experimental data, including the veryrecent results on commensurability effect and wavelength of the MOES.

[1] S. V. Andreev, arXiv:1701.05621 (2017). Under consideration in PRB.

[2] S. V. Andreev, Phys. Rev. B 94, 140501(R) (2016).

70



Creation and application of nanoscale optical barriers

Mikhail Baranov,1,2 Jan Budich,3 Andreas Elben,1,2 Mateusz Łacki,1,2 Hannes Pichler,1,2,4,5 AntoineSterdyniak,6 and Peter Zoller1,2

1 Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, Innsbruck, Austria2 Institute for Theoretical Physics, University of Innsbruck, Innsbruck, Austria

3 Department of Physics, University of Gothenburg, Gothenburg, Sweden4 ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA

5 Physics Department, Harvard University, Cambridge, Massachusetts, USA6 Max-Planck-Institute of Quantum Optics, Garching, Germany

Abstract: The generation of subwavelength optical barriers on the scale of tens of nanometers as conser-vative optical potentials for cold atoms is discussed [1]. These arise from nonadiabatic corrections toBorn-Oppenheimer potentials for dressed “dark states” in atomic Λ configurations. The subwavelengthbarriers represent an optical “Kronig-Penney” potential resulting in a distinctive band structure. Theycan also be used to create a double-layer or a double wire with subwavelength spacing and substantiallyincreased coupling energy scales compared to ordinary optical lattices. For a double-wire, this allowsobservation, for example, of Lifshitz transitions in Fermi gases in an experimentally realistic parameterregime [2]. Finally, inclusion of an interparticle dipole-dipole interaction leads to formation of “do-main wall molecules” and to unconventional Hubbard models with modulated in space interparticleinteractions [1].

[1] M. Łacki, M. A. Baranov, H. Pichler, and P. Zoller, Phys. Rev. Lett. 117, 133001 (2016).

[2] J. C. Budich, A. Elben, M. Łacki, A. Sterdyniak, M. A. Baranov, and P. Zoller, Phys. Rev. A 95, 043632 (2017).

71



Few particle systems: An exact analysis of the fractional quantum Hall effect

Nuria Barberan,1 Daniel Dagnino,2 Miguel Angel Garcia-March,1,3 Andrea Trombettoni,4 Josep Taron,1

and Maciej Lewenstein3

1 Departament de Fisica Quantica i Astrofisica, Facultat de Fisica, Universitat de Barcelona, E-08028 Barcelona, Spain2 Barcelona Center for Subsurface Imaging, Institute of Marine Sciences, CSIC, E-08003 Barcelona, Spain

3 ICFO-Institut de Ciencies Fotonoques, 08860 Castelldefels (Barcelona), Spain4 CNR-IOM DEMOCRITOS Simlation Center, Trieste, Italy

The analysis of the quantum Hall response of a small system of interacting ultracold bosonic atomsthrough the variation of its Hall resistivity against the applied gauge magnetic field provides a powerfulmethod to unmask its strongly correlated states in a quite exaustive way. We investigate the mechanismresponsible for the formation of plateaux in the resistivity in the lowest Landau level regime [1] andidentify the implied states in each plateau [2].

[1] N. Barberan, D. Dagnino, M. A. Garcia-March, A. Trombettoni, J. Taron, and M. Lewenstein, New J. Phys. 17, 125009 (2015).

[2] N. Barberan and J. Taron, Phys. Rev. A 95, 023609 (2017).

72



Droplets formation in trapped systems of dipolar bosons

Ferran Mazzanti, Adrian Macia, Juan Sanchez-Baena, and Jordi Boronat

Departament de Física, Universitat Politècnica de Catalunya, Barcelona (Spain)

Recent experiments [1,2] have demonstrated the unexpected formation of self-bound droplets of 164Dyatoms in a region of mean-field collapse. More interestingly, the resulting set of droplets is reported toarrange itself in a crystalline structure that becomes more clearly visible when the number of dropletsincreases. Several mechanisms have been suggested to produce this phenomenon, ranging from theinclusion of additional three-body forces [3,4], to the contribution of quantum fluctuations induced byLee-Huang-Yang corrections [5,6]. In any case, this is a clear situation where where beyond mean-fieldeffects determine the physics of the system. In this work [6] we use the exact Path Integral Ground Statetechnique to explore the properties of three-dimensional dipolar systems of bosons confined harmonically.By adding a repulsive two-body potential, we find a narrow window of interaction parameters wherestable ground-state configurations of several droplets in a crystalline arrangement are found. Thiseffect is entirely due to the interaction present in the Hamiltonian, without resorting to any additionalstabilizing mechanism. We thus analyze the number of droplets formed in terms of the Hamiltonianparameters, relate them to the corresponding s-wave scattering length, and discuss a simple scalingmodel for the density profiles.

[1] H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, and T. Pfau, Nature 530, 194 (2016).

[2] I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, and T. Pfau, Phys. Rev. Lett. 116, 215301 (2016).

[3] R. N. Bisset and P. B. Blakie, Phys. Rev. A 92, 061603 (2015).

[4] P. B. Blakie, Phys. Rev. A 93, 033644 (2016).

[5] F. Wächtler and L. Santos, Phys. Rev. A 93, 061603(R) (2016).

[6] F. Wächtler and L. Santos, Phys. Rev. A 94, 043618 (2016).

[7] A. Macia, J. Snchez-Baena, J. Boronat, and F. Mazzanti, Phys. Rev. Lett. 117, 205301 (2016).

73



Bose-Einstein condensates in a phase-modulated optical lattice

Citlali Cabrera-Gutiérrez,1 Eric Michon,1 Aéla Fortun,1 Mareike Berger,1 Juliette Billy,1 DavidGuéry-Odelin,1 Cyril Petitjean,2 and Peter Schlagheck2

1 Laboratoire Collisions Agrégats Réactivité, UPS.2 University of Liege

We report on our results obtained with rubidium-87 Bose-Einstein condensates in time-dependent opticallattices. We have (i) studied the traversal time of a wavepacket through the tunnel barriers of thelattice [1], (ii) investigated the BEC dynamics in phase-modulated lattices in various regimes. For thedynamics of BECs in phase-modulated optical lattice, one can distinguish different regimes dependingon the relative value of the frequency of modulation and that of the tunneling rate. In particular, if themodulation frequency is low, the physics is dominated by a tunneling rate renormalization. In the regimewhere the tunneling rate takes negative values a dynamical instability generates a new quantum state,commonly called a staggered state for which neighbouring sites acquire opposite phases. This phasetransition can be readily observed in momentum space after a time of flight expansion. The diffractionpeaks observed as a result of the spatial periodicity of a static optical lattice are modified: new peaksin between the former static peaks are observed. Interestingly this transition cannot be accounted forwith a standard mean-field approach. We investigated experimentally and numerically the dynamics ofnucleation of such staggered states [2].

[1] A. Fortun, C. Cabrera-Gutiérrez, G. Condon, E. Michon, J. Billy, and D. Guéry-Odelin Phys. Rev. Lett. 117, 010401 (2016).

[2] E. Michon, C. Cabrera-Gutiérrez, A. Fortun, M. Berger, C. Petitjean, P. Schlagheck, J. Billy, and D. Guéry-Odelin, to be submitted.

74



Phonon damping in a pair-condensed Fermi gas

Yvan Castin, Alice Sinatra, and Hadrien Kurkjian

LKB - ENS

We consider the interactions among phonons and the phonon lifetime in a pair-condensed Fermi gasin the BEC-BCS crossover in the collisionless regime. When the concavity of the dispersion relation isupwards at low wave number, the leading damping mechanism at low temperature is the Beliaev-Landauprocess 2 phonons↔ 1 phonon while, when the concavity is downwards, it is the Landau-Khalatnikovprocess 2 phonons↔ 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependenceon the interaction strength, we obtain a universal formula for the damping rate. This universal formulacorrects and extends the original analytic results of reference [1] for the 2 ↔ 2 processes in thedownward concavity case [2,3]. In the upward concavity case, for the Beliaev 1↔ 2 process for theunitary gas at zero temperature, we calculate the damping rate of an excitation with wave number qincluding the first correction proportional to q7 to the q5 hydrodynamic prediction [3].

[1] L. Landau and I. Khalatnikov, Teoriya vyazkosti Geliya-II, ZhETF 19, 637 (1949).

[2] H. Kurkjian, Y. Castin, and A. Sinatra, Landau-Khalatnikov phonon damping in strongly interacting Fermi gases, EPL 116, 40002

(2016) [https://hal.archives-ouvertes.fr/hal-01350507].[3] H. Kurkjian, Y. Castin, and A. Sinatra, Three-phonon and four-phonon interaction processes in a pair-condensed Fermi gas, to

appear in Annalen der Physik (2017) [https://hal.archives-ouvertes.fr/hal-01392846].

75



Topological properties and many-body phases of synthetic Hofstadter strips

Alessio Celi,1 Emanuele Tirrito,1 Samuel Mugel,1,4 Alexandre Dauphin,1 Pietro Massignan,1,2 RobertaCitro,3 Leticia Tarruell,1 Carlos Lobo,4 and Maciej Lewenstein5

1 ICFO The Institute of Photonic Science and the BIST2 UPC Universitat Politecnica de Catalunya

3 UNISA Università di Salerno4 University of Southampton

5 ICREA Institució Catalana de Recerca i Estudis Avançats

First I will discuss the topological properties of narrow Hofstadter strips, like the ones obtained byexploiting Raman-coupled Ny spin states of atoms as synthetic dimension [1,2]. I will show that suchnarrow systems can display not only edge states but also the topological properties associated to thebulk as in large systems, even if it reduces to just one lattice point (Ny = 3). In particular, I will showthat by Bloch oscillations it is possible to measure the Chern number C associated to the lowest band ofa large system pierced by the same flux with good accuracy, for Ny ≥ C + 2 [3]. Then, I will considerthe effect of interactions, focusing on the case of bosonic synthetic Hofstadter ladder. In particular, I willdescribe the phase diagram of the system in the hardcore boson limit, when the lattice is dimerized inthe real extended dimension. I will show by analytical and numerical means that melted vortex phasesand commensurate-incommesurate transitions, already found by other authors in real and synthetichomogeneous ladders, are easily accessible and controllable by varying the amount of the dimerization[4].

[1] O. Boada, A. Celi, J. I. Latorre, and M. Lewenstein, Phys. Rev. Lett. 108, 133001 (2012).

[2] A. Celi et al., Phys. Rev. Lett. 112, 043001 (2014).

[3] S. Mugel, A. Dauphin, P. Massignan, L. Tarruell, C. Lobo, M. Lewenstein, and A. Celi, to appear.

[4] E. Tirrito, R. Citro, M. Lewenstein, and A. Celi, in preparation.

76



Quench dynamics and excitation modes of a quantum phase transition in aspin-1 BEC

Michael Chapman,1 Bharath Hebbe,1 Matthew Boguslawski,1 Thai Hoang,1,2 and

1 Georgia Tech, Atlanta, GA USA2 Purdue U., W. Layfayette, IN USA

A symmetry breaking quantum phase transition (QPT) occurs when the emergent phase does not sharethe symmetries of the Hamiltonian. The excitations of the emergent ground state are classified intomassless Nambu-Goldstone modes and massive Anderson-Higgs modes. In a spin-1 ferromagnetic BEC,these modes can be observed as excitations of the spin population. In this work, we experimentallycharacterize such excitations in an 87Rb BEC [1]. Further, a non-adiabatic quench through the quantumcritical point (QCP) is described by Kibble-Zurek Mechanism, and it is characterized a power law relationbetween the system’s response time and the quench rate. We experimentally investigate this universalscaling for non-adiabatic quenches and show good agreement with the theoretical critical exponent[2]. Finally, we investigate adiabatic quenches through the QCP. Although adiabatic quenches are notpossible in the mean-field limit due the vanishing energy gap at the QCP, quantum finite-size effects inour small condensates open the gap slightly, which permits an adiabatic quench through the QCP. Usinga carefully optimized quench sequence, we demonstrate adiabatic crossing of the QCP [1].

[1] T. M. Hoang et al, Adiabatic quenches and characterization of amplitude excitations in a continuous quantum phase transition,

PNAS 113, 9475 (2016).

[2] M. Anquez et al, Quantum Kibble-Zurek mechanism in a spin-1 Bose-Einstein condensate, Phys. Rev. Lett. 116, 155301 (2016).

77



Novel spin dynamics and transport with cold atoms in tilted optical lattices

Andrew Daley,1 Anton Buyskikh,1 François Damanet,1 Chris Hooley,2 Dirk Schuricht,3 and David

Pekker4

1 Department of Physics and SUPA, University of Strathclyde, Glasgow, UK2 School of Physics and Astronomy and SUPA, University of St Andrews, St. Andrews, UK

3 Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Utrecht, The Netherlands4 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, USA

We study theoretically the out-of-equilibrium dynamics for two separate systems with chemical potentialgradients, motivated by recent experiments. The first involves Bosonic atoms in tilted optical lattices,where we show how coupled Ising spin chains can be realised in experiments with unusual forms ofthe coupling. This generalises previous theoretical and experimental work realising Ising chains withtransverse and longitudinal fields with cold atoms, but we show that the coupling entirely changes thecharacter of the system near phase transition points. We study this behaviour in and out of equilibriumby applying and optimising matrix product operator techniques for finite temperatures and projectedHilbert spaces. The second system involves transport induced by a chemical potential gradient whentwo reservoirs with paired fermions are coupled to a traps where they are tightly confined. Thiscould be realised with cold atoms in optical potentials, and is analogous to solid state systems withsuperconducting nanowires coupled to quantum dots. We show how input-output theory from quantumoptics can be generalised to describe these systems, identifying key features of the resulting transportproperties for particles moving between the reservoirs.

78



Many-body localization dynamics from gauge invariance

Marlon Brenes,1 Marcello Dalmonte,1 Markus Heyl,2 and Antonello Scardicchio1,3

1 The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy2 Max Planck Institute for the Physics of Complex Systems, Dresden 01187, Germany

3 INFN Sezione di Trieste, Via Valerio 2, 34127 Trieste, Italy

In this poster, we show how lattice gauge theories can display many-body localization dynamics in theabsence of disorder. Our starting point is the observation that, for some generic translationally invariantstates, Gauss law effectively induces a dynamics which can be described as a disorder average overgauge super-selection sectors. We carry out extensive exact simulations on the real-time dynamics of alattice Schwinger model, describing the coupling between U(1) gauge fields and staggered fermions.Our results show how memory effects and slow, double-logarithmic entanglement growth are presentin a broad regime of parameters—in particular, for sufficiently large interactions. These findings areimmediately relevant to cold atoms and trapped ions experiments realizing dynamical gauge fields, andsuggest a new and universal link between confinement and entanglement dynamics in the many-bodylocalized phase of lattice models.

79



Supersolid-like states in a spin-orbit coupled Bose-Einstein condensate

Thomas M. Bersano, Sean Mossman, Vandna Gokhroo, Peter Engels

Washington State University

Spin-orbit coupled BECs provide a powerful platform to investigate exotic quantum states. Amongthese, supersolids are particularly intriguing, exhibiting both superfluid and solid-like properties. Inour experiment, we employ a Raman dressing scheme to generate a spin-orbit dispersion. States withdifferent quasi-momentum are then coherently coupled by employing a suitably tailored optical lattice,effectively generating supersolid-like states. We demonstrate the coherent coupling mechanism by mea-suring Rabi oscillations between two quasi-momentum states. The current status and future direction ofthe experiment are discussed.

We acknowledge funding from NSF.

80



Engineering topological states of matter with ultracold two-electron atoms

Leonardo Fallani

University of Florence & LENS

I will report on recent experiments performed in Florence aimed at the study of topological states ofmatter with ultracold 173Yb fermions. Spin-orbit coupling, gauge fields and synthetic dimensions aregenerated by the quantum control of the spin degree of freedom and, in a novel experimental approach,by the manipulation of long-lived electronic states on a metrological ultranarrow clock transition [1].I will discuss current work and new perspectives towards the realization of new topological states ofultracold matter [2].

[1] L. F. Livi et al., PRL 117, 220401 (2016).

[2] F. Iemini et al., arxiv:1702.04733 (2017), PRL in press.

81



Vortex dynamics on a cylinder

Alexander Fetter,1,2 Nils Guenther,2 and Pietro Massignan2

1 Stanford University, CA2 ICFO, Barcelona

We study the dynamics of two-dimensional point vortices on the surface of a cylinder. This situationdiffers from the dynamics on a plane because of the periodicity around the circumference of the cylinder.This difference is particularly evident for a single vortex that must move around the circumference witha fixed speed. In addition, two vortices with the same charge can either circle around their commoncentroid or move separately in opposite directions around the circumference, depending on the initialconditions.

82



Integrable quantum tunneling models in ultracold physics

Angela Foerster

Instituto de Física da Universidade Federal do Rio Grande do Sul, Brazil

In this work we present a general construction of quantum integrable models for boson tunneling inmulti-well ultracold systems [1,2]. In particular we discuss a triple well Hamiltonian and a four-wellring model for bosons where the tunneling couplings between nearest-neighbour wells are not restrictedto be equal [3]. Finally we discuss the effects of breaking the integrability in some cases.

[1] L. H. Ymai, A. P. Tonel, A. Foerster, and J. Links, Quantum integrable multi-well tunneling models, arXiv:1606.00816 (2016).

[2] M. T. Batchelor and A. Foerster, Yang-Baxter integrable models in experiments: from condensed matter to ultracold atoms, J. Phys.

A: Math. Theor. 49, 173001 (2016).

[3] A. P. Tonel, L. H. Ymai, A. Foerster, and J. Links, Integrable model of bosons in a four-well ring with anisotropic tunneling, J. Phys.

A: Math. Theor. 48, 494001 (2015).

83



Giant many-body subradiant excitations in cold atomic ensembles

Gaetan Facchinetti,1,2 Stewart Jenkins,1 and Janne Ruostekoski1

1 Mathematical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom2 École Normale Supérieure de Cachan, 61 avenue du Président Wilson, 94235 Cachan, France

We show how strong light-mediated resonant dipole-dipole interactions between atoms can be utilizedin a control and storage of light. The method is based on a high-fidelity preparation of a collectiveatomic excitation in a single correlated subradiant eigenmode in a lattice. We demonstrate how a simplephenomenological model captures the qualitative features of the dynamics and sharp transmissionresonances that may find applications in sensing.

[1] PRL 117, 243601 (2016).

84



Few-body systems in a single-shot picture: Pauli crystals

Mariusz Gajda, Jan Mostowski, Tomasz Sowinski, and Magdalena Zaluska-Kotur

Institut of Physics, PAS, Warszaw, Poland

Recently developed techniques allow for simultaneous measurements of the positions of all ultracoldatoms in a trap with high resolution. Repeated single shot-measurements can be used to determineall correlations between particle positions. Here we discuss the possible outcomes of such single shotmeasurements in case of cloud of ultra-cold fermionic atoms. We show that the Pauli exclusion principleleads to correlations between particles’ positions that result in unexpected spatial structures formed bythe atoms. This happens even in the case of a few non-interacting Fermi atoms.

[1] M. Gajda, J. Mostowski, T. Sowinski, and M. Załuska-Kotur, EPL 115(2), 20012 (2016).

85



Open quantum dynamics of two distinguishable particles in a BEC

Miguel Á. García-March

ICFO, The Institute of Photonic Sciences

We study the dynamics of two quantum impurities immersed in a Bose-Einstein condensate as an opensystem. The behavior of the particles may be treated in the context of quantum Brownian motion asshowed in [1]. The two impurities are considered distinguishable and couple differently to the BEC. Wederive the set of coupled Langevin equations for the positions of the impurities. These equations containtwo memory kernels and are driven by two different colored noise terms. These noise terms derivefrom the degrees of freedom of the BEC, and depend on its parameters. We study the system underrealistic parameters, i.e, temperature, strength of the two different interactions between the BEC and theparticles, trapping frequency, etc. We consider the cases in which both particles are in the homogeneousmedia, one of them is trapped, and both are trapped. We consider both the situations with repulsive,attractive, and no interactions between the two impurities. We look to the long-time dynamics of bothparticles, discussing the role of memory effects and the presence of quantum phenomena.

[1] A. Lampo, S. H. Lim, M. A. García-March, and M. Lewenstein, arXiv:1704.07623 (2017).

86



Raman transfer of knotted optical vortices onto atomic Bose-Einsteincondensates

Simon Gardiner, I. G. Hughes, and F. Maucher

Joint Quantum Centre (JQC) Durham–Newcastle, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK

Recently there has been a growing interest in the dynamics of knotted vortex lines in BECs, withoutnecessarily considering concrete experimental means to excite such matter waves in a controlled fashion.We have studied the theoretical creation of knotted ultracold matter waves in Bose-Einstein condensatesvia coherent two-photon Raman transitions with a Λ level configuration, and their subsequent dynamics[1]. We have done this by taking advantage of the possibility to create knotted light fields (in the paraxiallimit) through astute superpositions of Laguerre–Gauss modes [2,3], and by numerical modelling ofthe three-dimensional Gross–Pitaevskii equation. The Raman transition allows an indirect transfer ofatoms from the internal state |a⟩ to the target state |b⟩ via an excited state |e⟩, that would be otherwisedipole-forbidden. This setup enables us to imprint three- dimensional knotted vortex lines embeddedin the probe field onto the matter-wave density profile in the target state. With this work we believewe have presented a setup with physically realistic parameters to create such knotted vortex lines inultracold matter waves.

[1] F. Maucher, S. A. Gardiner, and I. G. Hughes, New J. Phys. 18, 063016 (2016).

[2] M. R. Dennis, R. P. King, B. Jack, K. O’Holleran, and M. J. Padgett, Nat. Phys. 6, 118 (2010).

[3] M. R. Dennis, J. B. Gotte, R. P. King, M. A. Morgan, and M. A. Alonso, Opt. Lett. 36, 4452 (2011).

87



Simulating quantum spin models using ultracold Rydberg-excited ensembles inmagnetic microtrap arrays

Shannon Whitlock,1,2 Alexander Glaetzle,3,4,5 and Peter Hannaford6

1 Physikalisches Institut, Universität Heidelberg, Im Neuenheimer Feld 226, D-69120 Heidelberg, Germany2 IPCMS (UMR 7504) and ISIS (UMR 7006), Université de Strasbourg and CNRS, 67000 Strasbourg, France

3 Institut for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020, Innsbruck, Austria4 Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.

5 Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore6 Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne, Victoria 3122, Australia

We propose a scheme to simulate lattice spin models based on ultracold, long-range interacting Rydbergatoms stored in a large-spacing array of magnetic microtraps. Each spin is encoded in a collective spinstate involving a single nS or (n+1)S Rydberg atom excited from an ensemble of ground-state alkaliatoms prepared via Rydberg blockade. After the excitation laser is switched off, the Rydberg spin stateson neighbouring lattice sites interact via spin-spin interactions. To read out the collective spin states wepropose a single-Rydberg atom triggered avalanche scheme in which the presence of a single Rydbergatom conditionally transfers a large number of ground-state atoms in the trap to an untrapped statewhich can be readily detected by site-resolved absorption imaging. Such a quantum simulator shouldallow the study of quantum spin systems in almost arbitrary 1D and 2D configurations. This paves theway towards engineering exotic spin models, such as spin models based on triangular-symmetry latticeswhich can give rise to frustrated-spin magnetism.

88



Quantum simulation of lattice gauge theories in cold atoms

Philipp Hauke,1,2 Torsten Zache,2 Florian Hebenstreit,3 Valentin Kasper,4 Markus Oberthaler,1 Fred

Jendrzejewski,1 and Jürgen Berges2

1 Kirchhoff-Institute of Physics, Heidelberg University2 Institute of Theoretical Physics, Heidelberg University

3 Universität Bern4 Harvard University

Within the Standard Model of Particle Physics, the interaction between fundamental particles is describedby gauge theories. These theories have an enormous predictive power, but their theoretical treatment isexceedingly difficult. As a consequence, high-energy physics contains many unsolved problems such asthe dynamics of quarks and gluons during heavy-ion collisions, making gauge theories attractive targetsfor quantum simulation in cold atomic gases. In recent years, various proposals have been developed.All of these are, however, extremely challenging. Here, we argue that existing proposals do not makeuse of the full flexibility of lattice gauge theories: theories that differ only by irrelevant terms or bydifferent basis choices all reproduce the correct continuum limit. We use the example of (1+1)D QED todemonstrate the potential that lies still untapped here. For example, a suitable fermion discretizationtogether with a convenient basis choice for the Dirac algebra naturally gets rid of previous requirementsof staggered, spin-dependent optical lattices. With these and similar improvements, we advance towardsrealistic implementations of lattice gauge theories in optical-lattice setups.

89



Majorana quasi-particles protected by Z2 angular momentum conservation

Fernando Iemini,1 Leonardo Mazza,2 Leonardo Fallani,3,4 Peter Zoller,5,6 Rosario Fazio,1,7 and MarcelloDalmonte1

1 Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste, Italy2 Departement de Physique, Ecole Normale Superieure / PSL Research University, CNRS, 24 rue Lhomond, F-75005 Paris, France

3 Department of Physics and Astronomy, University of Florence, I-50019 Sesto Fiorentino, Italy4 LENS European Laboratory for Nonlinear Spectroscopy, I-50019 Sesto Fiorentino, Italy

5 Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria6 Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria

7 NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56126 Pisa, Italy

We show how angular momentum conservation can stabilise a symmetry-protected quasi-topologicalphase of matter supporting Majorana quasi-particles as edge modes in one-dimensional cold atomgases. We investigate a number-conserving four-species Hubbard model in the presence of spin-orbitcoupling. The latter reduces the global spin symmetry to an angular momentum parity symmetry, whichprovides an extremely robust protection mechanism that does not rely on any coupling to additionalreservoirs. The emergence of Majorana edge modes is elucidated using field theory techniques, andcorroborated with density-matrix-renormalization-group simulations. Our results pave the way towardthe observation of Majorana edge modes with alkaline-earth-like fermions in optical lattices, where allbasic ingredients for our recipe—spin-orbit coupling and strong inter-orbital interactions—have beenexperimentally realized over the last two years.

90



Controlling the quantum fluctuations of strongly magnetic atoms

Krzysztof Jachymski,1 Rafal Oldziejewski,2 Jan Kumlin,1 and Hans Peter Büchler1

1 Institute for Theoretical Physics III, University of Stuttgart, Stuttgart, Germany2 Center for Theoretical Physics, Polish Academy of Sciences, Warsaw, Poland

Recent experiments with ultracold erbium and dysprosium atoms revealed the existence of new phe-nomena such as droplet formation which can only be described by going beyond the mean field picture.We study the Lee-Huang-Yang corrections arising for a gas of dipolar atoms confined in external latticepotential and show that it is possible to control the magnitude of the correction by manipulating thedepth and orientation of the lattice. We also calculate realistic low energy scattering amplitude which isused as effective potential in the Bogoliubov method and show that corrections to the commonly usedBorn approximation can be significant, especially close to scattering resonances. Different interactionterms can be studied in experiment via trap spectroscopy of two atoms trapped in anisotropic potential.

91



Experiments with ultracold triplet ground-state molecules

Alan Jamison,1 Timur Rvachov,1 Hyungmok Son,1,2 Julianna Park,1 Ariel Sommer,1 Martin Zwierlein,1

and Wolfgang Ketterle1

1 MIT2 Harvard University

We report experimental determination of the triplet molecular potentials of NaLi, previously unobserved.With this information, we use STIRAP to transfer Feshbach molecules to the triplet ground state. Theseultracold molecules have both electric and magnetic dipole moments and lifetimes of at least 100ms.This creates unique opportunities in both quantum controlled chemistry and simulation of many-bodysystems of interest in condensed matter.

92



Cold collision experiments at Feshbach resonances far above threshold

Niels Kjærgaard,1 Ryan Thomas,1 Milena Horvath,1 Amita Deb,1 and Eite Tiesinga2

1 Department of Physics, QSO–Centre for Quantum Science, and Dodd-Walls Centre for Photonic and Quantum Technologies,University of Otago, Dunedin, New Zealand

2 Joint Quantum Institute and Center for Quantum Information and Computer Science, National Institute of Standards and

Technology and University of Maryland, Gaithersburg, Maryland 20899, USA

Resonances are a paradigm of quantum mechanical scattering. Their manifestation become particularlyclear for ultracold atoms due to the pristine nature of these systems. In the past we have observed thestriking anisotropic scattering halos resulting from shape resonances that are set up by centrifugal barriersin the cold collisions between nanokelvin atomic clouds. Examples include an `= 1 p-wave resonancefor fermionic potassium [1] and an ` = 2 d-wave resonance for bosonic rubidium [2]. More recently wehave employed an optical collider [3] based on steerable tweezer beams [4] to investigate scattering atmagnetic Feshbach resonances. While experiments on ultracold gases so far almost exclusively havebeen conducted at threshold (in the zero energy limit) our scheme allows us to operate above thresholdand to map out the resonance in a parameter space spanned by both energy and magnetic field. Wewill present the case of measurements on a narrow, highly inelastic interstate resonance of rubidium[5]. This will be contrasted to our results for a broad interspecies elastic scattering resonance betweenpotassium and rubidium displaying the telltale asymmetric Beutler-Fano line shape.

[1] R. Thomas, K. O. Roberts, E. Tiesinga, A. C. J. Wade, P. B. Blakie, A. B Deb, and N. Kjærgaard, Multiple scattering dynamics of

fermions at an isolated p-wave resonance, Nature Communications 7, 12069 (2016).

[2] N. R. Thomas, N. Kjærgaard, P. S. Julienne, and A. C. Wilson, Imaging of s and d partial-wave interference in quantum scattering

of identical bosonic atom, Physical Review Letters 93, 173201 (2004).

[3] A. Rakonjac, A. B. Deb, S. Hoinka, D. Hudson, B. J. Sawyer, and N. Kjærgaard, Laser based accelerator for ultracold atoms,

Optics Letters 37, 1085 (2012).

[4] K. O. Roberts, T. McKellar, J. Fekete, A. Rakonjac, A. B. Deb, and N. Kjærgaard, Steerable optical tweezers for ultracold atom

studies, Optics Letters 39, 2012 (2014).

[5] M. S. J Horvath, R. Thomas, E. Tiesinga, A. B. Deb, and N. Kjærgaard, Above threshold scattering about a Feshbach resonance for

ultracold atoms in an optical collider, arXiv:1704.07109 (2017).

93



Bose polaron as an instance of quantum Brownian motion

Aniello Lampo

ICFO – The Institute of Photonic Sciences

We study the dynamics of a quantum impurity immersed in a Bose-Einstein condensate as an openquantum system in the framework of the quantum Brownian motion model. We derive a generalizedLangevin equation for the position of the impurity. The Langevin equation is an integrodifferentialequation that contains a memory kernel and is driven by a colored noise. These result from consideringthe environment as given by the degrees of freedom of the quantum gas, and thus depend on itsparameters, e.g. interaction strength between the bosons, temperature, etc. We study the role of thememory on the dynamics of the impurity. When the impurity is untrapped, we find that it exhibits asuper-diffusive behavior at long times. We find that back-flow in energy between the environment andthe impurity occurs during evolution. When the particle is trapped, we calculate the variance of theposition and momentum to determine how they compare with the Heisenberg limit. One important resultof this paper is that we find position squeezing for the trapped impurity at long times. We determine theregime of validity of our model and the parameters in which these effects can be observed in realisticexperiments.

94



Vortex reconnections and rebounds in trapped atomic Bose-Einsteincondensates

Giacomo Lamporesi,1 Simone Serafini,1 Luca Galantucci,2 Elena Iseni,1 Tom J. Bienaimé,1 Russel N.

Bisset,1 Carlo F. Barenghi,2 Franco Dalfovo,1 and Gabriele Ferrari1

1 INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento2 Joint Quantum Centre (JQC) Durham-Newcastle and School of Mathematics and Statistics, Newcastle University

Quantized vortex interaction mechanisms in atomic condensates have been widely studied in rotatingsystems, with the self organization of alike vortices into a regular Abrikosov lattice, and also in flatquasi-2D systems, where vortex and antivortices coexist and affect their mutual dynamics. In both thesekinds of systems vortices align (or anti align) along a single preferential direction. This is given by therotation axis in the first case or by the confined direction in the second one. The interaction mechanismamong vortices is hence mainly restricted to a 2D problem. We study the interaction mechanismsbetween vortices in an axially symmetric, elongated BEC. In such a geometry vortices tend to align in aradial plane and can therefore assume any orientation in such plane. Due to the asymmetric confinementthe associated phase pattern varies substantially in a region not larger than the transverse ThomasFermi radius, therefore initially far away vortices orbit around the center of the BEC unaffected by thepresence of the other until they approach and start interacting, changing their relative velocity and theirrelative orientation. Depending on the approaching configuration the two vortices might bounce orreconnect. We combine [1] experimental observations of real-time vortex dynamics and Gross-Pitaevskiisimulations and provide a clear picture of 3D interaction mechanism between vortex filaments.

[1] S. Serafini et al., to be published in PRX (2017).

95



Bose polarons at finite temperature and strong coupling

Pietro Massignan,1,2 Nils Guenther,2 Maciej Lewenstein,2,3 and Georg Bruun4

1 Departament de Física, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain2 ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain

3 ICREA, 08010 Barcelona, Spain4 Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark

In the past decade, intense studies have been devoted to the study of impurities in a polarized ultracoldFermi sea, and by now their properties are relatively well understood [1]. The complementary casewhere the bath is bosonic is presently of great interest, both theoretically and experimentally [2,3].Here we investigate the temperature dependence of a mobile impurity in a dilute Bose gas, the Bosepolaron, for wide a range of impurity-bath interactions. Using a diagrammatic resummation schemedesigned to include scattering processes important at finite temperature T , we show that the phasetransition of the environment to a Bose-Einstein condensate at the critical temperature Tc leads toseveral non-trivial effects. The attractive polaron present at T = 0 fragments into two quasiparticlestates for finite temperature whenever |a| ¦ aB , with a and aB the impurity-boson and boson-bosonscattering lengths. While the quasiparticle with higher energy disappears at Tc , the ground statequasiparticle remains well-defined across Tc . Its energy depends non-monotonically on temperature,featuring a minimum at Tc , after which it increases towards zero, and the quasiparticle eventuallybecomes overdamped due to strong scattering with thermally excited bosons [4].

[1] P. Massignan, M. Zaccanti, and G. M. Bruun, Polarons, dressed molecules, and itinerant ferromagnetism in ultracold Fermi gases,

Rep. Prog. Phys. 77, 034401 (2014).

[2] N. B. Jørgensen et al., Observation of attractive and repulsive polarons in a Bose-Einstein condensate, Phys. Rev. Lett. 117,

055302 (2016).

[3] M.-G. Hu et al., Bose polarons in the strongly interacting regime, Phys. Rev. Lett. 117, 055301 (2016).

[4] N.-E. Guenther, P. Massignan, M. Lewenstein, and G. M. Bruun, in preparation (2017).

96



Detecting topological defects and implementing supersymmetric quantummechanics

Ludwig Mathey1,2,3

1 Zentrum für Optische Quantentechnologien, Universität Hamburg, 22761 Hamburg, Germany2 Institut fürLaserphysik, Universität Hamburg, 22761 Hamburg, Germany

3 The Hamburg Center for Ultrafast Imaging, Luruper Chaussee 149, Hamburg 22761, Germany

We present two recent studies. In the first, Ref. [1], we present a method of measuring topologicaldefects of Bloch bands in ultra-cold atom systems. For a hexagonal lattice, the fermionic atoms areprepared in a band insulating state of the lower band. The lattice amplitude is then modulated withan off-resonant frequency. After time of flight expansion, a momentum dependent modulation withthe same frequency is observed. The relative phase between the driving and the response modulationgives access to topological defects of the band structure, in an efficient and versatile manner. In thesecond study, Ref. [2], we propose to implement and detect supersymmetric quantum mechanics inultra-cold atom systems. We present a interferometric protocol that gives a sharply peaked response ifthe two subsystems are supersymmetric. We provide two examples for implementing this protocol, aone-dimensional system, for which we provide a full numerical demonstration, and a two-dimensionalsystem with a synthetic gauge field.

[1] Matthias Tarnowski, Marlon Nuske, Nick Fläschner, Benno Rem, Dominik Vogel, Lukas Freystatzky, Klaus Sengstock, Ludwig

Mathey, Christof Weitenberg, arXiv:1703.02813 (2017).

[2] M. Lahrz, C. Weitenberg, L. Mathey, arXiv:1703.02863 (2017).

97



Laughlin-like states in bosonic and fermionic 1D gases with syntheticdimension

Marcello Calvanese Strinati,1,2 Eyal Cornfeld,3 Davide Rossini,4,1 Simone Barbarino,5,1 MarcelloDalmonte,6,7,8 Rosario Fazio,6 Eran Sela,3 and Leonardo Mazza2

1 NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56126 Pisa, Italy2 Département de Physique, Ecole Normale Supérieure / PSL Research University, CNRS, 24 rue Lhomond, F-75005 Paris, France

3 Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, IL-69978 Tel Aviv, Israel4 Dipartimento di fisica, Università di Pisa, I-56126 Pisa, Italy

5 SISSA-International School for Advanced Studies, Via Bonomea 265, I-34136 Trieste, Italy6 ICTP, Strada Costiera 11, 34151 Trieste, Italy

7 Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria8 Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria

The combination of interactions and static gauge fields plays a pivotal role in our understandingof strongly-correlated quantum matter. Cold atomic gases endowed with a synthetic dimension areemerging as an ideal platform to experimentally address this interplay in quasi-one-dimensional systems.A fundamental question is whether these setups can give access to pristine two-dimensional phenomena,such as the fractional quantum Hall effect, and how.Using numerical simulations based on matrix-product states, we show that unambiguous signatures ofbosonic and fermionic Laughlin-like states can be observed and characterized in synthetic ladders. Wetheoretically diagnose these Laughlin-like states focusing on the chiral current flowing in the ladder, onthe central charge of the low-energy theory, and on the properties of the entanglement entropy.Our work provides a qualitative and quantitative guideline towards the observability and understandingof strongly-correlated states of matter in synthetic ladders. In particular, we unveil how state-of-the-art experimental settings constitute an ideal starting point to progressively tackle two-dimensionalstrongly interacting systems from a ladder viewpoint, opening a new perspective for the observation ofnon-Abelian states of matter.

[1] M. Calvanese Strinati, E. Cornfeld, D. Rossini, S. Barbarino, M. Dalmonte, R. Fazio, E. Sela, and L. Mazza, arXiv:1612.06682

(2016).

98



Two impurities in a BEC: From Yukawa to Efimov attracted Bose polarons

Pascal Naidon

RIKEN

The Yukawa attraction (screened 1/r interaction) is known to arise between two particles exchangingbosons, such as nucleons exchanging mesons. On the other hand, at the three-body level, the Efimovattraction (1/r2 three-body interaction) can emerge from resonant two-body interactions, leading to theexistence of the Efimov three-body bound states. In this work, I look into how the mediated interactionbetween two particles immersed in a Bose-Einstein condensate can go from a Yukawa attraction to anEfimov attraction, as the strength of the particle-boson interaction is increased. This has implications onthe many-body physics of Bose polarons, which are currently being realised in ultra-cold mixtures ofatoms.

[1] https://arxiv.org/abs/1607.04507.

99



Hofstadter butterfly evolution in the space of two-dimensional Bravais lattices

Mehmet Oktel and Firat Yilmaz

Department Of Physics, Bilkent University, Ankara 06800 TURKEY

The self-similar energy spectrum of a particle in a periodic potential under a magnetic field, knownas the Hofstadter butterfly, is determined by the lattice geometry as well as the external field. Recentrealizations of artificial gauge fields and adjustable optical lattices in cold atom experiments necessitatethe consideration of these self-similar spectra for the most general two-dimensional lattice. In a previouswork, we investigated the evolution of the spectrum for an experimentally realized lattice which wastuned by changing the unit cell structure but keeping the square Bravais lattice fixed. We now considerall possible Bravais lattices in two dimensions and investigate the structure of the Hofstadter butterflyas the lattice is deformed between lattices with different point symmetry groups. We model the opticallattice by a sinusoidal real space potential and obtain the tight binding model for any lattice geometryby calculating the Wannier functions. We introduce the magnetic field via Peierls substitution andnumerically calculate the energy spectrum. The transition between the two most symmetric lattices, i.e.the triangular and the square lattice displays the importance of bipartite symmetry featuring deformationas well as closing of some of the major energy gaps. The transition from the square to rectangular andfrom the triangular to centered rectangular lattices are analyzed in terms of coupling of one-dimensionalchains. We calculate the Chern numbers of the major gaps and Chern number transfer between bandsduring the transitions. We use gap Chern numbers to identify distinct topological regions in the space ofBravais lattices.

[1] arXiv:1703.08810 (2017).

100



Entangling two non-identical atoms via Rydberg blockade

David Papoular,1 Peng Xu,2 Georgy Shlyapnikov,3 and Mingsheng Zhan2

1 LPTM, CNRS & Univ. Cergy-Pontoise, France2 WIPM, Chinese Academy of Sciences, Wuhan, China

3 LPTMS, CNRS & Univ. Paris-Sud, France

We report on the first experimental realization of the controlled-NOT (C-NOT) quantum gate andentanglement for two non-identical atoms and demonstrate a negligible crosstalk between two atomqubits. The experiment is based on a strong Rydberg blockade for 87Rb and 85Rb atoms confined in twosingle-atom optical traps separated by 3.8 µm. The raw fidelities of the C-NOT gate and entanglementare 0.73± 0.01 and 0.59± 0.03, respectively, without any correction for atom loss or trace loss. Ourwork, together with the technologies of single-qubit gate and C-NOT gate developed for identicalatoms, forms basic building blocks for simulating many-body systems with multi-species interactions. Ithas applications in quantum computing and quantum metrology, since heteronuclear systems exhibitadvantages in low crosstalk and in memory protection.

101



Two intriguing examples for topological effects in ultracold atoms

Axel Pelster

Physics Department and Research Center OPTIMAS, Technical University of Kaiserslautern, Germany

At first, we analyze the ground-state properties of anyons in a one-dimensional lattice using the Anyon-Hubbard Hamiltonian [1]. To this end we map the hopping dynamics of correlated anyons to anoccupation dependent hopping Bose-Hubbard model using the fractional Jordan-Wigner transformation.In particular, we apply a modified Gutzwiller mean-field approach and the density-matrix renormalizationgroup in order to calculate the quasi-momentum distribution of anyons, which interpolates between Bose-Einstein and Fermi-Dirac statistics. Afterwards, we investigate the extended hard-core Bose-Hubbardmodel on the triangular lattice as a function of spatial anisotropy with respect to both hopping andnearest-neighbor interaction strength [2]. At intermediate anisotropy frustration effects dominate andan incommensurate supersolid phase emerges, which is characterized by incommensurate density orderas well as an anisotropic superfluid density. We demonstrate that this intermediate phase results fromthe proliferation of topological defects in the form of quantum bosonic domain walls.

[1] G. Tang, S. Eggert, and A. Pelster, Ground-state properties of anyons in a one-dimensional lattice, New J. Phys. 17, 123016

(2015).

[2] X.-F. Zhang, S. Hu, A. Pelster, and S. Eggert, Quantum domain walls induce incommensurate supersolid phase on the anisotropic

triangular lattice, Phys. Rev. Lett. 117, 193210 (2016).

102



Space-born Bose-Einstein condensation for precision interferometry

Ernst M. Rasel

Leibniz Universität Hannover

Interferometers employing Bose-Einstein condensates will be at the heart the next generation quantumsensors, promising to improve on both, precision and accuracy. The presentation will report on therecent successful launch of the DLR-mission MAIUS-1 exploring methods for BEC interferometry ona sounding rocket in space. These methods are instrumental for creating novel miniaturized sensorsbased on atom chips as transportable devices both for ground and space operation. Beyond fundamentalphysics, fields of application are geodesy or generally Earth observation.This work is part of the CollaborativeResearch Center geo-Q of the Deutsche Forschungsgemeinschaft(SFB 1128), dq-mat (SFB 1227), and is supported by the GermanSpace Agency (DLR) with fundsprovided by the Federal Ministry for Economic Affairs and Energy (BMWi) due to an enactment of theGerman Bundestag under grant numbers DLR 50WM1552-1557 (QUANTUS-IV-Fallturm), as well as bythe Centre for Quantum Engineering and Space-Time Research (QUEST-LFS)

103



Exploring interacting topological insulators with ultracold atoms: The syntheticCreutz-Hubbard model

Johannes Jünemann,1,2 Angelo Piga,3 Shi-Ju Ran,3 Maciej Lewenstein,3,4 Matteo Rizzi,1 and AlejandroBermudez5,6

1 Johannes Gutenberg- Universität, Mainz (Germany)2 MAINZ - Graduate School Materials Science in Mainz (Germany)

3 ICFO-Institut de Ciencies Fotoniques, Castelldefels (Spain)4 ICREA-Institució Catalana de Recerca i Estudis Avançats, Barcelona (Spain)

5 Swansea University (UK)6 Instituto de Física Fundamental, IFF-CSIC, Madrid (Spain)

Understanding the robustness of topological phases of matter in the presence of strong interactions, andsynthesising novel strongly-correlated topological materials, lie among the most important challengesof modern theoretical and experimental physics. Here we present a complete theoretical analysis ofthe Creutz-Hubbard ladder, a paradigmatic model that provides a neat playground to address thesechallenges. We put special attention to the competition of exotic topological phases and orbital quantummagnetism in the regime of strong interactions and identify the universality class of the different phasetransitions, highlighting an interesting splitting of central charges induced by interactions. Theseresults are furthermore confirmed and extended by extensive numerical simulations and analysis ofthe entanglement properties. Moreover, we propose how to experimentally realize this model and testits phase diagram in a synthetic ladder, made of two internal states of ultracold fermionic atoms in aone-dimensional optical lattice. Our work paves the way towards quantum simulators of interactingtopological insulators with cold atoms.

[1] arXiv:1612.02996 (2016).

104



Time crystals

Krzysztof Sacha,1 Dominique Delande,2 and Luis Morales-Molina3

1 Jagiellonian University in Krakow2 Laboratoire Kastler Brossel, Paris

3 Pontificia Universidad Catolica de Chile, Santiago

Time crystals are related to spontaneous quantum self-organization of many body systems in time inanalogy to the formation of space crystals. Research of time crystals can be divided into two branches.In the first branch researchers look for systems that can reveal spontaneous breaking of time translationsymmetry. In the other branch condensed matter phenomena are investigated in time crystals with thehelp of periodically driven systems similarly as space periodic potentials are used to model propertiesof space crystals in solid state physics. We show that discrete time translation symmetry can bespontaneously broken and the so-called discrete time crystals can form [1]— the predicted phenomenonthat has been demonstrated in recent experiments [2,3]. We show also that a number of solid statephenomena can be observed in the time domain in periodically driven systems. That is, Andersonlocalization in the time domain induced by disorder in time [4-6] and Mott insulator phase in the timedomain [4] can realized in ultra-cold atomic gases.

[1] K. Sacha, Phys. Rev. A 91, 033617 (2015).

[2] J. Zhang et al., arXiv:1609.08684 (2016).

[3] S. Choi et al., arXiv:1610.08057 (2016).

[4] K. Sacha, Sci. Rep. 5, 10787 (2015).

[5] K. Sacha and D. Delande, Phys. Rev. A 94, 023633 (2016).

[6] D. Delande, L. Morales-Molina, and K. Sacha, arxiv:1702.03591 (2017).

105



Many-body localization in system with a completely delocalized single-particlespectrum

Yoav Sagi,1 Yevgeny Bar Lev,2 and David Reichman2

1 Department of Physics, Technion – Israel Institute of Technology, Haifa 32000, Israel2 Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA

We study many-body localization (MBL) in a one-dimensional Fermi Hubbard model with random on-siteinteractions [1]. While for this model all single-particle states are trivially delocalized, it is shown thatfor sufficiently strong disorder the model is many-body localized. This model provides a convenientplatform to study pure MBL phenomenology, since Anderson localization in this model does not exist.By examining various forms of the interaction term a dramatic effect of symmetries on charge transportis demonstrated. We suggest a possible realization in a cold atom experiment. Finally, we report onrecent progress in building a new degenerate Fermi gas experiment at the Technion.

[1] Phys. Rev. B 94, 201116(R) (2016).

106



Superfluid-insulator transitions for strongly interacting one-dimensionalbosons in a shallow periodic and disordered potentials

G. Boéris,1 L. Gori,2 M. D. Hoogerland,3 A. Kumar,2 E. Lucioni,2 L. Tanzi,2 M. Inguscio,2,4 T. Giamarchi,5

C. D’Errico,2 G. Carleo,1 G. Modugno,2 and Laurent Sanchez-Palencia1,6

1 Laboratoire Charles Fabry, Institut d’Optique, CNRS, Univ Paris-Saclay, 2 avenue Augustin Fresnel, F-91127 Palaiseau cedex, France2 LENS and Dipartimento di Fisica e Astronomia, Universita di Firenze, and CNR-INO, 50019 Sesto Fiorentino, Italy

3 Department of Physics, University of Auckland Private Bag 92019, Auckland, New Zealand4 INRIM, 10135 Torino, Italy

5 Department of Quantum Matter Physics, University of Geneva, 24 quai Ernest-Ansermet, 1211 Geneva, Switzerland6 Centre de Physique Theorique, Ecole Polytechnique, CNRS, Univ. Paris-Saclay, Palaiseau Cedex, France

We investigate the superfluid-insulator transition of one-dimensional interacting bosons in both deepand shallow periodic potentials, as well as quasi-periodic and disordered potentials. We compare atheoretical analysis based on quantum Monte Carlo simulations in continuum space and Luttinger liquidapproach with experiments on ultracold atoms with tunable interactions and optical potential depth.For periodic potentials, experiments and theory are in excellent agreement. This study provides aquantitative determination of the critical parameters for the Mott transition and defines the regimes ofvalidity of widely used approximate models, namely, the Bose-Hubbard and sine-Gordon models. Forquasi-periodic and disordered potentials, signatures of the Bose glass phase transition are found anduniversal properties are discussed.

[1] G. Boéris, L. Gori, M. D. Hoogerland, A. Kumar, E. Lucioni, L. Tanzi, M. Inguscio, T. Giamarchi, C. D’Errico, G. Carleo, G.

Modugno, and L. Sanchez-Palencia, Phys. Rev. A 93, 011601(R) (2016).

107



Novel method to study disordered frustrated antiferromagnets in opticallattices

Abel Yuste, David Castells, Mariona Moreno-Cardoner, and Anna Sanpera

Universitat Autònoma de Barcelona

Disordered quantum antiferromagnets in two-dimensional compounds have been a focus of interestin the last years due to their exotic properties. However, with very few exceptions, the ground statesof the corresponding Hamiltonians are notoriously difficult to simulate making their characterizationand detection very elusive, both theoretically and experimentally. Here we propose a method to signalquantum disordered antiferromagnets by doing exact diagonalization in small lattices using randomboundary conditions and averaging the observables of interest over the different disorder realizations.

[1] A. Yuste, M. Moreno-Cardoner, and A. Sanpera, Phys. Rev B 95, 195167 (2017).

108



Quantum fluctuations in low-dimensional dipolar condensates

Luis Santos

Institute of Theoretical Physics, Leibniz Universität Hannover

Quantum fluctuations are not only more relevant in weakly interacting dipolar gases than in non-dipolarones, as recently revealed experimentally, but as we show they may have radically different properties[1]. After introducing the concept of quantum stabilization of dipolar droplets in 3D geometries, Iwill focus on 1D Bose gases, showing that due to the peculiar momentum dependence of the dipolarinteractions in 1D, the Lee-Huang-Yang (LHY) correction presents a very different density-dependencethan that expected in non-dipolar systems. Moreover, dipolar gases allow for a surprising novel regimein which the condensate remains 1D but the quantum corrections are crucially affected by the transversaldirections. As a result, the LHY correction changes from attractive to repulsive for a growing density, evenif the BEC remains 1D. I will discuss the relevant consequences that this peculiar quantum correction hason the properties of 1D dipolar condensates, which may be readily observable in on-going experimentswith highly magnetic atoms.

[1] D. Edler et al., arXiv:1610.09176 (2016).

109



Angular momentum in spin-orbit coupled Bose-Einstein condensed gases

Sandro Stringari and Chunlei Qu

University of Trento

Spin-orbit coupling (SOC) deeply affects the superfluid and rotational behavior of a Bose-Einteincondensate [1,2]. Angular momentum can be produced by adding a position dependent detuning(hereafter simply called detuning) in the SOC Hamiltonian, avoiding the rotation of the trap and ofthe laser set-up. In this contribution we present recent results concerning: i) The violation of theirrotationality constraint for the superfluid motion, the emergence of diffused vorticity and of the rigidvalue of the moment of inertia [2]. ii) The excitation of the scissors mode, caused by the suddenswitching off of the detuning [3]. iii) The emergence of Foucault like precession of the dipolar modes ofthe condensate, caused by the presence of the detuning [3].

[1] Yi-Cai Zhang, Zeng-Qiang Yu, Tai Kai Ng, Shizhong Zhang, Lev Pitaevskii, and Sandro Stringari, Superfluid density of a spin-orbit

coupled Bose gas, Phys. Rev. A 94, 033635 (2016).

[2] Sandro Stringari, Diffused vorticity and moment of inertia of a spin-orbit coupled Bose-Einstein condensate, Phys. Rev. Lett. 118,

145302 (2017).

[3] Chunlei Qu and Sandro Stringari, in preparation.

110



Recurrences in an isolated quantum many-body system

B. Rauer,1 S. Erne,1,2,3 T. Schweigler,1 F. Cataldini,1 M. Tajik,1 and Jörg Schmiedmayer1

1 Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien2 Institut für Theoretische Physik, Universität Heidelberg

3 Kirchhoff-Institut für Physik, Universität Heidelberg

The evolution of an isolated quantum system is unitary. If the system becomes large and its constituentsinteract one is not able to follow the evolution of the complex many body eigenstates. A system outof equilibrium it will ‘relax’ for practical observables [1]. The steady state reached can be describedby a Generalized Gibbs Ensemble [2]. In our present study [3] we ask the question if, under whichconditions the initial coherence can be revived.Even though the evolution of an isolated quantum system is unitary, the complexity of interacting many-body systems prevent the observation of recurrences of quantum states for all but the smallest systems.For large systems one cannot access the full complexity of the quantum states and the requirementsto observe a recurrence in experiments reduces to being close to the initial state with respect to theemployed observable. Selecting an observable connected to the collective excitations in one-dimensionalsuper-fluids, we demonstrate recurrences of coherence and long range order in an interacting quantummany-body system containing thousands of particles. This opens up a new window into the dynamics oflarge quantum systems even after they reached a transient thermal-like state.Supported by the DFG/FWF: SFB ISOQUANT and the EU through the ERC-AdG QuantumRelax

[1] M. Gring et al., Science 337, 1318 (2012); T. Langen et al., Nature Physics 9, 640 (2013).

[2] T. Langen et al., Science 348 207 (2015).

[3] B. Rauer et al., arXiv:1705.08231 (2017).

111



Non-equilibrium dynamics of ultracold atoms in optical lattices studied withYtterbium atoms

Yoshiro Takahashi, Takafumi Tomita, Shuta Nakajima, Yosuke Takasu, Hideki Ozawa, and Shintaro Taie

Department of Physics, Graduate School of Science, Kyoto University

We will report our recent study of non-equilibrium physics using ytterbium quantum gases loaded inoptical lattices. We investigate non-equilibrium dynamics of ultracold bosons after sudden quench froma Mott insulator state by lowering the lattice depth. By exploiting the high-resolution laser spectroscopyand time-of-flight analysis in one-, two-, and three-dimensional optical lattices, we can separatelymeasure the temporal evolution of kinetic and interaction energies, and investigate the propagation ofphase coherence over distant sites. We also study the dynamics subjected to a slow ramp-down of theoptical lattice in the presence of engineered dissipation for Bose-Hubbard system. We find that strongdissipation favors the Mott insulating state: the melting of the Mott insulator is delayed and the growthof the phase coherence is suppressed. Other topics such as topological charge pumping will be alsobriefly mentioned.

112



Quantum anomaly and thermodynamics of a 2D Fermi gas via collectiveoscillations

Tyson Peppler,1 Paul Dyke,1 Marta Zamorano,1,2 Sascha Hoinka,1 Brendan Mulkerin,1 Hui Hu,1 Xia-JiLiu,1 Peter Hannaford,1 and Chris Vale1

1 Centre for Quantum and Optical Sciences, Swinburne University of Technology, Melbourne 3122, Australia2 Departement de Physique, École Normale Supérieure, 75005 Paris, France

We present an experimental and theoretical study of collective oscillations in strongly interactingFermi gases in the crossover from two to three dimensions. By measuring the frequency of the radialbreathing mode, we map the evolution between the known 2D and 3D limits due to the differentpolytropic equations of state. This provides insight into the thermodynamic character of the gasthroughout the dimensional crossover and its dependence on the interaction strength. Furthermore, in2D, the Hamiltonian for a gas with delta-function interactions is classically scale invariant. However,renormalisation in a quantum treatment introduces a length scale which breaks scale invariance leadingto a so-called quantum anomaly. Our measurements of the collective mode frequency in the 2D regimelie above the scale-invariant classical prediction for a range interaction strengths, consistent with theexistence of the quantum anomaly.

113



Faraday excitations in a Bose-Einstein condensate

Peter van der Straten,1 Lei Liao,2 Jasper Smits,1 and Henk Stoof2

1 Debye Institute for Nanomaterials, Utrecht, The Netherlands2 Institute for Theoretical Physics, Utrecht, The Netherlands

Parametric excitations of a Bose-Einstein condensate can be induced by modulating the radial trapfrequency of the trap. By shortly pulsing the radial trap frequency we induce quadrupole oscillations ofthe cloud in both directions and after some time we observe the emergence of a Faraday pattern. Theperiod of the Faraday pattern depends strongly on the aspect ratio of the trap. Since the Faraday patternis a standing wave sound mode, it allows us to determine with a large accuracy the speed of sound in thecondensate. The dynamics of the Faraday pattern is studied using phase-contrast imaging, which allowsfor the detection of the pattern of a single cloud for 100 consecutive instances. We study theoreticallythe interplay between the Faraday mode and the radial quadrupole mode of the condensate. In themodel we want to establish the condition for which the Faraday pattern occurs.

114



Observation of a dynamical topological phase transition in the non-equilibriumdynamics of ultracold quantum gases in driven optical lattices

Nick Flaschner,1,2 Dominik Vogel,1 Matthias Tarnowski,1,2 Benno Rem,1,2 Dirk-Sören Lühmann,1 MarkusHeyl,4 Jan Budich,5,6 Ludwig Mathey,1,2,3 Klaus Sengstock,1,2,3 and Christof Weitenberg1,2

1 Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany2 The Hamburg Center for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany

3 Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany4 Physik Department, Technische Universität München, 85747 Garching, Germany

5 Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, 6020 Innsbruck, Austria6 Institute for Theoretical Physics, University of Innsbruck, 6020 Innsbruck, Austria

Ultracold atoms are a versatile system to emulate solid-state physics including the fascinating phenomenaof gauge fields and topological band structures. By circular driving of a hexagonal optical lattice, weengineer the Berry curvature of the Bloch bands and realize a Haldane-like model. We have developed afull momentum-resolved state tomography of the Bloch states, which allows measuring the distributionof Berry curvature and obtaining the Chern number [1]. Furthermore, we study the time evolution of themany-body wave function after a sudden quench of the lattice parameters and observe the appearance,movement, and annihilation of dynamical vortices in reciprocal space. We identify them as Fisher zerosin the Loschmidt amplitude and define them as a dynamical equivalent of a topological order parameter,which suddenly changes its value at critical evolution times [2]. Our measurements constitute the firstobservation of a so-called dynamical phase transition and address the intriguing question of the relationbetween this phenomenon and the equilibrium phase transition in the system.

[1] Flaschner et al., Science 352, 1091 (2016).

[2] Flaschner et al., arXiv:1608.05616 (2016).

115



Exploring itinerant ferromagnetism with ultracold repulsive Fermi mixtures

Matteo Zaccanti,1,2 Francesco Scazza,1,2 Giacomo Valtolina,1,2,3 Andrea Amico,1,2 Alessio Recati,4,5

Tilman Enss,6 Alessia Burchianti,1,2 Massimo Inguscio,1,2 and Giacomo Roati1,2

1 INO-CNR, Sesto Fiorentino, Italy2 LENS and Dipartimento di Fisica e Astronomia, Università di Firenze, Sesto Fiorentino, Italy

3 JILA, University of Colorado Boulder, USA4 INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, Povo, Italy

5 Ludwig-Maximilians-Universität München, Germany6 University of Heidelberg, Germany

Ferromagnetism is a spectacular manifestation of strong repulsive interactions between itinerant fermionsin condensed matter systems. Whether short-ranged repulsion alone is sufficient to stabilize ferromag-netic correlations in the absence of other effects, such as peculiar band dispersions or orbital couplings,is, however, still debated [1].Here, I will discuss recent and ongoing experiments addressing such an intriguing problem with ultracoldFermi mixtures. By studying spin dynamics and collective excitations we explored the ferromagneticbehaviour of a repulsive Fermi gas of 6Li atoms artificially prepared in a domain-wall state [2]. Whereasfermion pairing characterizes the ground state of the system, our experiments provide signaturessuggestive of a metastable ferromagnetic phase supported by strong repulsion in excited scatteringstates. I will then discuss the possibility to realize long-lived repulsive Fermi mixtures of Lithium andChromium atoms, whose unique mass ratio enables an extraordinary suppression of atom recombinationinto paired states in the regime of strong repulsion.

[1] P. Massignan et al., Polarons, dressed molecules and itinerant ferromagnetism in ultracold Fermi gases, Rep. Prog. Phys. 77,

034401 (2014).

[2] G. Valtolina et al., Exploring the ferromagnetic behaviour of a repulsive Fermi gas via spin dynamics, Nat. Phys., Advance Online

Publication (2017).

116



Dynamics of quantum many-body systems far from equilibrium: Interactionquenches

Robert Zillich and Michael Kobler

Institute for Theoretical Physics, Johannes Kepler University

Recent experiments have shown that it is possible to bring a Bose gas into the regime of large scatteringlength with an interaction quench via a Feshbach resonance, revealing for example a rapid evolution ofthe two-body contact, but a slow evolution of the three-body contact. We present our recent work onthe nonlinear response of bosonic many-body systems, applied to interaction quenches. We find, forexample, that a quench from weak to strong interactions can lead to a localization of the perturbationin the pair distribution function. For these studies we develop a generalization of the hypernetted-chainEuler-Lagrange method to time dependence, based on a Jastrow-Feenberg variational ansatz for themany-body wave function. This allows to investigate the dynamics of a many-body system far fromequilibrium.

117



Cavity-enhanced transport of charge

Guido Pupillo

University of Strasbourg

We theoretically investigate charge transport through electronic bands of a mesoscopic one-dimensionalsystem, where inter-band transitions are coupled to a confined cavity mode, initially prepared in itsvacuum. This coupling leads to light-matter hybridization where the dressed fermionic bands interactvia absorption and emission of dressed cavity-photons. Using a self-consistent non-equilibrium Green’sfunction method, we compute electronic transmissions and cavity photon spectra and demonstrate howlight-matter coupling can lead to an enhancement of charge conductivity in the steady-state. Dependingon the ratio between cavity loss rate and electronic bandwidth, the system dynamics involves either acollective or an individual response of Bloch states, and explain how this affects the current enhancement.We show that under certain experimentally relevant conditions the charge conductivity enhancementcan reach orders of magnitudes.

[1] David Hagenmüller, Johannes Schachenmayer, Stefan Schütz, Claudiu Genes, and Guido Pupillo, Cavity-enhanced transport of

charge, arXiv:1703.00803 (2017).

118



Impurities immersed in a BEC: Quantum simulator of the polaron?

Luis A. Peña Ardila,1,2 Thomas Pohl,2 and Stefano Giorgini3

1 Max Plank Institute for the Physics of Complex Systems, Dresden, Germany2 University of Aarhus, Aarhus, Denmark

3 INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, Povo, Italy

We investigate the properties of an impurity immersed in a Bose gas at zero temperature using bothanalytical and Quantum-Monte Carlo methods. The interaction between bosons are modeled by ahard-sphere potential with scattering length a , whereas the impurity-boson interaction is modeled bya short-range attractive square-well potential, where both the sign and the strength of the scatteringlength b can varied by adjusting the well depth.We characterize the repulsive and attractive polaron branch by calculating the binding energy andthe effective mass . Furthermore, we study the structure of the bosonic bath such as the boson-bosoncorrelation function and the density profile around the impurity. For resonant interactions betweenthe impurity and the bosonic bath, the Ground state properties are also investigated as well as EfimovEffects [1]. The implication for the phase diagram of binary Bose-Bose mixtures is also discussed [1] .Our predictions for more realistic cases [2] are compared with recent experiments realising the BosePolaron [3.4]. We also discuss more complicated interactions between the impurity and the bosonic bath.For this case we consider a Quasi-2D Dipolar Bose gas at zero temperature. Furthermore, the impurity-Bose interaction is dipolar. Using perturbation theory, the Ground-state properties are investigatedbased on the low-energy Fröhlich Hamiltonian. We studied the role of the long-range interaction forthis model in contrast with contact interactions previously investigated [5]. The polaron in this model isformed by the impurity dressed by the Low-energy modes of the Dipolar Bose gas: Dipolar Bose Polaron.

[1] L. A. P. Ardila and S. Giorgini, Phys. Rev. A 92, 033612 (2015).

[2] L. A. P. Ardila, W. Casteels, and Thomas Pohl, In preparation (2017).

[3] Phys. Rev. Lett. 117, 055302 (2016).

[4] Phys. Rev. Lett. 117, 055301 (2016).

[5] L. A. P. Ardila and S. Giorgini, Phys. Rev. A 94, 063640 (2016).

119



Parity-time-symmetric quantum critical phenomena

Yuto Ashida,1 Shunsuke Furukawa,1 and Masahito Ueda1,2

1 Department of Physics, University of Tokyo2 RIKEN CEMS

Synthetic nonconservative systems with parity-time (PT) symmetric gain-loss structures can exhibitunusual spontaneous symmetry breaking that accompanies spectral singularity [1]. Recent studiessuch as in optics [2], optomechanics [3] and atomic physics [4] have revealed intriguing physicalproperties of PT-symmetric systems, yet many-body correlations still play no role. Here by extendingthe idea of PT symmetry to strongly correlated many-body systems, we find that a combination ofspectral singularity and quantum criticality yields an exotic universality class which has no counterpartin known critical phenomena [5]. Introducing the PT-symmetric non-Hermitian sine-Gordon model, weperform the perturbative renormalization group (RG) analysis and show that semi-circular RG flowsanomalously enhance superfluid correlation in the PT-symmetry-broken phase, in stark contrast to theBerezinskii-Kosterlitz-Thouless (BKT) transition. We also conduct numerical calculations based on theexact diagonalization method and infinite time-evolving decimation (iTEBD) method, and obtain theresults that are consistent with the RG analyses. Finally, we propose an experimental scheme to test ourtheoretical predictions using quantum gas microscopy [6].

[1] C. M. Bender and S. Boettcher, Phys. Rev. Lett. 80, 5243 (1998).

[2] A. Regensburger et al., Nature 488, 167 (2012).

[3] J. Jing et al., Phys. Rev. Lett. 113, 053604 (2014).

[4] P. Peng et al., Nature Phys. 12, 1139 (2016).

[5] Y. Ashida, S. Furukawa, and M. Ueda, arXiv:1611.00396 (to appear in Nat. Commun.).

[6] W. S. Bakr et al., Nature 462, 74 (2009).

120



Artificial gauge fields in the honeycomb lattice

Ulrike Bornheimer,1,2,3 Christian Miniatura,1,2,3,4,5 and Benoît Grémaud1,2,3,6

1 Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore2 MajuLab, CNRS-UNS-NUS-NTU International Joint Research Unit, UMI 3654, Singapore

3 Physics Department, Faculty of Science, National University of Singapore, 2 Science Drive 3, 117551 Singapore4 INLN, Université de Nice-Sophia Antipolis, CNRS; 1361 Route des Lucioles, F-06560 Valbonne, France

5 Institute of Advanced Studies, Nanyang Technological University, 60 Nanyang View, Singapore 639673, Singapore6 Laboratoire Kastler Brossel, Ecole Normale Supérieure CNRS, UPMC; 4 Place Jussieu, F-75005 Paris, France

We investigate the phase diagram of spin-1 bosons propagating in a 2D honeycomb lattice and subjectedto a SU(3) spin-orbit coupling and interactions. In the first stage, we focus on a particular realization ofa topological insulator for non-interacting bosons in the honeycomb lattice, analogous to PRL 109(23),235308 (2012). This physical situation is equivalently obtained from a gauge transformation of theHarper model and can be realized experimentally. We focus on the analysis of the single-particle spectrumand the edge states obtained when open boundary conditions are imposed in one direction. Indeed, theirvery existence reflects the topology of the bulk system through the bulk-edge correspondence. We alsoexamine the localization properties of these edge states, stability and dependence on the symmetries ofthe Hamiltonian. Exotic quantum phases are expected to emerge from the interplay of interactions andtopological properties: the ground state might have a non-trivial spin texture and the excitation bandstructure might have non-zero Chern numbers. We are exploring these properties either directly withinthe Bose-Hubbard model or by use of the effective Heisenberg model in the strong interaction limit.

121



Spontaneous avalanche dephasing in large Rydberg ensembles

Thomas Boulier,1,2 Eric Magnan,1,2 Carlos Bracamontes,1 James Maslek,1 Elizabeth Goldschmidt,3

Jeremy Young,1 Alexey Gorshkov,1,4 Steve Rolston,1 and James Porto1

1 Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, College Park, Maryland20742 USA

2 Laboratoire Charles Fabry, Institut dOptique Graduate School, CNRS, UniversitÃl’ Paris-Saclay, 91127 Palaiseau cedex, France3 United States Army Research Laboratory, Adelphi, Maryland 20783 USA

4 Joint Center for Quantum Information and Computer Science, National Institute of Standards and Technology and the University of

Maryland, College Park, Maryland 20742 USA

Rydberg atoms are a strong candidate for the implementation of quantum information processing, ormore generally for coherent control in large interacting systems. However recently there has beenconcerns [1] about this approach due to the observation of a rapid onset of decoherence in largeensembles [2,3]. This has been especially visible in the difficulty of realizing Rydberg dressing foratomics ensemble of ∼ 100 atoms or more. We provide experimental support [2] for the hypothesis thatthis is due to the avalanche-like onset of off-diagonal dipole exchange interactions, fueled by blackbodytransitions to nearby Rydberg states of opposite parity. Making a fully microscopic model has provendifficult as it appears far beyond mean-field arguments: high order correlations play an important role,as can be expected for an off-diagonal interaction. The ubiquitousness of Rydberg-Rydberg blackbodytransitions at room temperature and the always-resonant nature of dipole exchange interactions make itan interesting challenge and argue for deeper studies into the matter. We present here measurementsand analysis that unveil this mechanism, and explore several possibilities to reduce its impact.

[1] M. Saffman, Journal of Physics B: Atomic, Molecular and Optical Physics 49, 202001 (2016).

[2] J. A. Aman et al., PRA 93, 043425 (2016).

[3] E. A. Goldschmidt et al., PRL 116, 113001 (2016).

122



Nonlinear scattering of atomic bright solitons in disorder

Thomas Bourdel, Amaudric Boissé, Lauriane Fouché, Guillaume Salomon, Alain Aspect, and StevenLepoutre

Laboratoire Charles Fabry, Institut d’Optique, CNRS, Univ Paris-Sud - 2, Avenue Augustin Fresnel, 91127 PALAISEAU CEDEX, France

We observe nonlinear scattering of 39K atomic bright solitons launched in a one-dimensional (1D) speckledisorder. We directly compare it with the scattering of non-interacting particles in the same disorder.The atoms in the soliton tend to be collectively either reflected or transmitted, in contrast with thebehavior of independent particles in the single scattering regime, thus demonstrating a clear nonlineareffect in scattering. The observed strong fluctuations in the reflected fraction, between zero and 100%,are interpreted as a consequence of the strong sensitivity of the system to the experimental conditionsand in particular to the soliton velocity. This behavior is reproduced in a mean-field framework byGross-Pitaevskii simulations, and mesoscopic quantum superpositions of the soliton being fully reflectedand fully transmitted are not expected for our parameters. We discuss the conditions for observing suchsuperpositions, which would find applications in atom interferometry beyond the standard quantumlimit.

[1] A. Boissé, G. Berthet, L. Fouché, G. Salomon, A. Aspect, S. Lepoutre and T. Bourdel, EPL 117, 10007 (2017).

[2] S. Lepoutre, L. Fouché, A. Boissé, G. Berthet, G. Salomon, A. Aspect, and T. Bourdel, PRA 94, 053626 (2016).

123



Ultracold atoms trapped in subwavelength potentials

Caroline Busquet, Maxime Bellouvet, Simon Bernon, and Philippe Bouyer

LP2N, Université de Bordeaux, IOGS, CNRS

Ultracold atoms used as quantum simulators offer an alternative way to simulate many-body systemsbehavior in condensed matter. Indeed, we can create artificial matter with optical lattices : thestationnary wave reproduces the potential wells in the crystalline structure. Moreover, the advantageof using cold atoms is that the parameters of the simulated crystal are well controlled so that we canunderstand its properties [1]. The common approach for generating optical lattices is to use interferingcounterpropagating laser beams. The lattice period ` is limited by the interfringe (∼ λ/2). Here, wepropose a different approach to create subwavelength 2D lattices (`∼ 50 nm) by modulating Casimir-Polder (CP) forces [2] in the near field of a nanostructure. Transverse confinement is realized withstates engineering. The resulting lattices allow the enhancement of energy scales [3], which benefitsthe simulation of strongly-correlated physics. Furthermore, we implement a subwavelength imagingtechnique to investigate this system, also based on states engineering.

[1] T. Esslinger, Annual Review of Condensed Matter Physics 1, (2010).

[2] H. B. G. Casimir and D. Polder, Physical Review 73, 360 (1948).

[3] M. Gullans et al., Physical Review Letters 109, 235309 (2012).

124



Efimov physics in resonantly interacting Bose gases

Roman Chapurin, Xin Xie, Michael Van de Graaff, Jun Ye, and Eric Cornell

JILA, NIST, and University of Colorado

Resonantly interacting Bose gases possess an infinite spectrum of Efimov trimer states with geometricscaling. This scaling is independent of the precise details of two- and three-body potentials. We exploresuch universality in two systems with two different atomic species. In a 85Rb system we create anappreciable population of Efimov trimers and describe their decay processes [1]. In a 39K system wereport on our recent progress in measuring the molecular binding energies and the Efimov inelastic lossparameter.

[1] Catherine Klauss et al. Observation of Efimov molecules created from a resonantly-interacting Bose gas, arXiv:1704.01206 (2017).

125



2D spin-orbit coupling for Rb BEC

Wei Sun,1,2 Zhan Wu,1,2 Bao-Zong Wang,1,2,3 Xiao-Tian Xu,1,2 Chang-Rui Yi,1,2 Long Zhang,2,3 YoujinDeng,1,2 Xiong-Jun Liu,3 Shuai Chen,1,2 and Jian-Wei Pan1,2

1 Shanghai Branch, National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Scienceand Technology of China, Shanghai 201315, China.

2 Chinese Academy of Sciences (CAS) Center for Excellence and Synergetic Innovation Center of Quantum Information and QuantumPhysics, University of Science and Technology of China, Hefei, Anhui 230026, China.

3 International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.

Cold atoms with laser-induced spin-orbit (SO) interactions provide a platform to explore quantum physicsbeyond natural conditions of solids. Here we propose and experimentally realize two-dimensional (2D)SO coupling and topological bands for a Rubidium-87 degenerate gas through an optical Raman lattice,without phase-locking or fine-tuning of optical potentials. A controllable crossover between 2D and 1DSO couplings is studied, and the SO effects and nontrivial band topology are observed by measuring theatomic cloud distribution and spin texture in momentum space. Our realization of 2D SO coupling withadvantages of small heating and topological stability opens a broad avenue in cold atoms to study exoticquantum phases, including topological superfluids. Furthermore, a more stable and robust scheme of2D Spin-Orbit coupling is implemented for further study of the topological quantum gases.

126



Critical velocity of counterflowing superfluids

Frédéric Chevy,1 Sébastien Laurent,1 Shuwei Jin,1 Matthieu Pierce,1 Tarik Yefsah,1 Ionut Danaila,2 and

Philippe Parnaudeau3

1 Ecole Normale Supérieure2 Université de Rouen

3 Université de Poitiers

Recent experiments on dual Bose-Fermi superfluids [1,2] have suggested the existence of a novelmechanism for the breakdown of superfluidity in superfluid counterflows [3,4,5]. This mechanism isassociated with the creation of pairs of excitations in the two superfluids and competes with the classicalLandau’s argument. We studied this competition by solving numerically the Gross-Pitaevskii equationfor a mixture of Bose-EInstein condensates. We characterized the coupling between the center-of-massoscillations of the two BEC with their Bogoliubov modes. We demonstrated the existence of two couplingmechanisms that we relate to Landau’s argument and its extension.

[1] I. Ferrier-Barbut, M. Delehaye, S. Laurent, A. T. Grier, M. Pierce, B. S. Rem, F. Chevy, and C. Salomon, A mixture of Bose and

Fermi superfluids, Science 45, 1035 (2014).

[2] M. Delehaye, S. Laurent, I. Ferrier-Barbut, S. Jin, F. Chevy, and C. Salomon, Critical velocity and dissipation of an ultracold

Bose-Fermi counterflow, Phys. Rev. Lett. 115, 265303 (2015).

[3] F. Chevy, Counterflow in a doubly superfluid mixture of bosons and fermions, Phys. Rev. A 91, 063606 (2015).

[4] M. Abad, A. Recati, S. Stringari, and F. Chevy, Counterflow instability of a quantum mixture of two superfluids, Eur. Phys. J. D

69, 126 (2015).

[5] Y. Castin, I. Ferrier-Barbut, and C. Salomon, La vitesse critique de Landau d’une particule dans un superfluide de fermions,

Comptes Rendus Physique 16, 241 (2015).

127



Dipolar macro-droplet of Erbium stabilized by quantum fluctuations

Lauriane Chomaz,1 Simon Baier,1 Daniel Petter,1 Giulia Faraoni,1 Jan-Hendrick Becher,1 Manfred J.Mark,1,2 and Francesca Ferlaino1,2

1 Institut für Experimentalphysik, Universität Innsbruck, 6020 Innsbruck, Österreich2 Institut für Quantenoptik und Quanteninformation, Österreichische Akademie der Wissenschaften, 6020 Innsbruck, Österreich

Due to their large magnetic moment and exotic electronic configuration, atoms of the lanthanide familysuch as dysprosium and erbium are an ideal platform for exploring the competition between inter-particle interactions of different origins and different behaviors. Recently, a novel phase of dilute droplethave been reported when changing the ratio of the contact and dipole-dipole interactions and settingthe mean-field interactions to attractive in an ultracold bosonic dysprosium gas [1]. This has beenattributed to the distinct non-vanishing beyond-mean-field effects when canceling the mean interactionin presence of DDI and is thus expected to be general to dipolar gases [2,3,4]. Here, we report onthe investigation of dilute droplet physics in a bosonic erbium gas. By precise control of the s-wavescattering length, we quantitatively probe the Bose-Einstein condensate (BEC)-to-droplet phase diagramand the rich underlying dynamics [5]. In a prolate geometry, we observe a crossover from a BEC to adense macro-droplet of 104 atoms, and characterize the special properties of this state. By this mean wequantitatively demonstrate the stabilizing role of the quantum fluctuations.

[1] H. Kadau et al., Nature 530, 194 (2016).

[2] I. Ferrier-Barbut et al., Phys. Rev. Lett. 116, 215301 (2016).

[3] F. Wächtler and L. Santos, Phys. Rev. A 93, 061603 (2016).

[4] R. N. Bisset, R. M. Wilson, D. Baillie, and P. B. Blakie, Phys. Rev. A 94, 033619 (2016).

[5] L. Chomaz et al., Phys. Rev. X 6, 041039 (2016).

128



Vortex lattice melting in a boson ladder in artificial gauge field

Roberta Citro,1 Edmond Orignac,2 Mario Di Dio,3 and Stefania De Palo3

1 Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno and Unità Spin-CNR, Via Giovanni Paolo II, 132, I-84084Fisciano (Sa), Italy

2 Univ Lyon, Ens de Lyon, Univ Claude Bernard, CNRS, Laboratoire de Physique, F-69342 Lyon, France3 CNR-IOM-Democritos National Simulation Centre, UDS Via Bonomea 265, I-34136, Trieste, Italy

4 Dipartimento di Fisica Teorica, Università Trieste, Trieste, Italy

We consider a two-leg boson ladder in an artificial U(1) gauge field and show that, in the presenceof interleg attractive interaction, the flux induced Vortex state can be melted by dislocations. Forincreasing flux, the Meissner to Vortex transition in the commensurate-incommensurate universalityclass [1,2] is replaced, first, by an Ising transition from the Meissner state to a charge density wave takesplace, then, at higher flux, by a melted Vortex phase. This is established via a disorder point whereincommensuration develops in the rung current correlation function and in momentum distribution.Finally, the quasi-long range ordered Vortex phase is recovered for sufficiently small interaction. Ourpredictions for the observables, such as the spin current and the static structure factor, could be testedin current experiments with cold atoms in bosonic ladders.

[1] M. Di Dio, S. De Palo, E. Orignac, R. Citro, and M.-L. Chiofalo, Phys. Rev. B 92, 060506 (2015).

[2] E. Orignac, R. Citro, M. Di Dio, S. De Palo, and M. L. Chiofalo, New J. Phys. 18, 055017 (2016).

129



Detection of Zak phases and topological invariants in a chiral quantum walk oftwisted photons

Filippo Cardano,1 Alessio D’Errico,1 Alexandre Dauphin,2 Maria Maffei,1,2 Bruno Piccirillo,1 Corrado de

Lisio,1,3 Giulio De Filippis,1,3 Vittorio Cataudella,1,3 Enrico Santamato,1,3 Lorenzo Marrucci,1,4 MaciejLewenstein,2,5 and Pietro Massignan2

1 Dipartimento di Fisica, Universita di Napoli Federico II2 ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology

3 CNR-SPIN4 CNR-ISASI, Institute of Applied Science and Intelligent Systems

5 ICREA - Institucio Catalana de Recerca i Estudis Avançats

Initially discovered in condensed matter, topological phases have so far been simulated in a variety ofsynthetic systems (ultracold atoms in optical lattices, photonic bandgap materials, mechanical systems,...). Current theoretical research is showing that periodically-driven systems generate much richer andmore complex topological properties than their static counterparts. Therefore, the accurate detection ofthese topological properties is a key challenge.Here, we derive and design an efficient theoretical method which allows to measure the Zak phases ofone dimensional systems with chiral symmetry by direct imaging of single particle dynamics in theirbulk. We then confirm experimentally our theoretical findings by measuring the two independent Zakphases of a chiral quantum walk realized by twisted photons, i.e., in a photonic platform exploiting thespin and orbital angular momenta of light. Combining the two phase windings, they provide a completeand robust topological characterization of this periodically-driven system [1].Finally, this method does not require a filled band, nor the application of a force, but simply relies onthe observation of real-time dynamics. This may be extremely beneficial in systems where uniform bandfilling is not easy to achieve, such as the ones not affected by the Pauli principle.

[1] F. Cardano et al., arXiv:1610.06322 (to appear in Nature Communications).

130



Minimal model for bistability in a driven-dissipative superfluid

Matthew Reeves and Matthew Davis

ARC Centre of Excellence for Future Low-Energy Electronics Technologies, School of Mathematics and Physics, University of

Queensland, St Lucia QLD 4072, Australia

Labouvie et al. [1] recently studied the dynamical behaviour of a Bose-Einstein condensate in a one-dimensional optical lattice. One site was designated as the system, whereas the remaining sites weretreated as a particle reservoir. The experiment studied the dynamics and long-time steady state of thesystem following the introduction of controllable single particle dissipation. They discovered that therewas a range of dissipation rates for which the system exhibited bistability — the steady-state at longtimes depended on whether the system was initially full or empty. Labouvie et al. also provided evidenceof critical slowing down in the dynamics, suggesting a possible non-equilibrium phase transition.Here we develop a minimal model for this system using the classical field methodology for ultracoldBose gases [2]. Particles are injected into the system at finite energy corresponding to the chemicalpotential of the reservoir. These subsequently undergo thermalisation and can lead to to the formationof a Bose-Einstein condensate, dependent on the rate of dissipation. We provide a theoretical basis forunderstanding the experimental observations.

[1] R. Labouvie, B. Santra, S. Heun, and H. Ott, Phys. Rev. Lett. 116, 235302 (2016).

[2] P. B. Blakie, A. S. Bradley, M. J. Davis, R. J. Ballagh, and C. W. Gardiner, Advances in Physics 57, 363 (2008).

131



Phase-fluctuating condensates are fragmented: An experimental benchmark forself-consistent quantum many-body calculations

Oleksandr V. Marchukov and Uwe R. Fischer

Seoul National University

We study zero-temperature quantum phase fluctuations in harmonically trapped one-dimensionalinteracting Bose gases, using the self-consistent multiconfigurational time-dependent Hartree method.In a regime of mesoscopic particle numbers and moderate contact couplings, it is shown that the phase-fluctuating condensate is properly described as a fragmented condensate. In addition, we demonstratethat the spatial dependence of the amplitude of phase fluctuations significantly deviates from what isobtained in Bogoliubov theory. Our results can be verified in currently available experiments. Theytherefore provide an opportunity both to experimentally benchmark the multiconfigurational time-dependent Hartree method, as well as to directly observe, for the first time, the quantum many-bodyphenomenon of fragmentation in single traps.

[1] https://arxiv.org/abs/1701.06821.

132



Topological order in finite-temperature and driven dissipative systems

Michael Fleischhauer

Dept. of Physics and Research Center OPTIMAS, Univ. of Kaiserslautern

I introduce a classification scheme for topological phases applicable to finite- temperature states aswell as stationary states of driven, dissipative systems based on a generalization of the many-bodypolarization. The polarization can be used to probe the topological properties of non-interacting andinteracting closed and open systems alike and remains a meaningful quantity even in the presence ofmoderate particle- number fluctuations. As examples, I discuss an open-system version of a topologicalThouless pump in the steady state of one-dimensional lattices driven by Markovian reservoirs [1] andthe finite-temperature Rice-Mele and Hofstadter-Hubbard models. Here a non-trivial winding of themany-body polarization identifies topological invariants. The winding is shown to be robust againstHamiltonian perturbations as well as homogeneous dephasing and particle losses. I will also discuss ameasurement scheme that allows to detect the polarization winding of finite-temperature and driven,dissipative systems and interactions through a quantized transport in an auxiliary quantum system.

[1] D. Linzner et al., Phys. Rev. B 94, 201105 (2016).

133



RF-dressed atom wave-guides, shells and lattices for quantum technologyapplications: Test of Landau-Zener theory

Kathryn Burrows,1 German Sinuco-Leon,1 Helene Perrin,2 and Barry Garraway1

1 University of Sussex, UK2 CNRS, UMR 7538, University Paris 13, Sorbonne Paris City,

Dressing atoms with radio-frequency and microwave radiation opens up new possibilities for a BEC innew types of trap and in new topologies such as spherical surfaces and in waveguide loops [1,2] as wellas in well studied lattices [3,4]. This is because of the flexibility inherent in the vector coupling of amagnetic dipole moment to electromagnetic fields which can be varied in time, frequency, orientationand space. This may in turn result in quantum technology applications to sensing (with ring traps andgyroscopes [5,6]), metrology, interferometry and atomtronics.In this work we present recent results on Landau-Zener losses in dressed adiabatic traps which givemore accurate estimates of their constraints [7]. We also present recent results on potential for spacemissions and on RF-dressed lattices where microwave pulses are used to manipulate the atoms [3,4].

[1] B. M. Garraway and H. Perrin, Topical Review: Recent developments in trapping and manipulation of atoms with adiabatic

potentials, J. Phys. B 49, 172001 (2016).

[2] H. Perrin and B. M. Garraway, Trapping atoms with radio-frequency adiabatic potentials, in Advances in Atomic, Molecular and

Optical Physics, to appear (2017).

[3] G. A. Sinuco-León and B. M. Garraway, Radio-frequency dressed lattices for ultracold alkali atoms, New J. Phys. 17, 053037

(2015); Addressed qubit manipulation in radio-frequency dressed lattices, New J. Phys. 18, 035009 (2016).

[4] G. A. Sinuco-León and B. M. Garraway, Addressed qubit manipulation in radio-frequency dressed lattices, New J. Phys. 18,

035009 (2016).

[5] O. Morizot, Y. Colombe, V. Lorent, H. Perrin, and B. M. Garraway, Ring trap for ultracold atoms, Phys. Rev. A 74, 023617

(2006).

[6] G. Sinuco-León, K. Burrows, A. S. Arnold, and B. M. Garraway, Inductively guided circuits for ultracold dressed atoms, Nat.

Commun. 5, 5289 (2014).

[7] K. Burrows, B. M. Garraway, and H. Perrin, Non-adiabatic losses from RF-dressed cold atom traps: beyond the Landau-Zener

model, to be submitted (2017).

134



Bulk topology of thin quantum Hall ribbons

Dina Genkina,1,2 Lauren Aycock,1,2,3 Alina Escalera,1,2 Mingwu Lu,1,2 Hsin-I Lu,1,2 and Ian Spielman1,2

1 University of Maryland - College Park2 National Institute of Standards and Technology

3 Cornell University

Individual bands of 2D lattices can be characterized in terms of a Chern number, that also defines thenumber of conducting edge channels at the boundary of finite systems. We experimentally explore howsmall a finite size system can be while still exhibiting these properties. Our experiments were performedin a synthetic-dimension lattice of Bose-condensed 87Rb [1,2,3] with about 1/3 flux quanta per unit cell.We applied a force along lattice’s long dimension to sample the entire Brillouin zone, and demonstratedthat for both a 3-site wide strip and a 5-site wide strip the bands still manifested non-trivial “bulk”topology [4]. However, the topologically protected edge modes were absent in the 3-site wide systemand only appeared in the 5-site wide system.

[1] A. Celi, P. Massignan, J. Ruseckas, N. Goldman, I. B. Spielman, G. Juzeliunas, and M. Lewenstein, Synthetic gauge fields in

synthetic dimensions, Phys. Rev. Lett. 112, 043001 (2014).

[2] B. K. Stuhl, H.-I Lu, L. M. Aycock, D. Genkina, and I. B. Spielman, Visualizing edge states with an atomic Bose gas in the quantum

Hall regime, Science 349, 1514 (2015).

[3] M. Mancini, G. Pagano, G. Cappellini, L. Livi, M. Rider, J. Catani, C. Sias, P. Zoller, M. Inguscio, M. Dalmonte, and L. Fallani,

Observation of chiral edge states with neutral fermions in synthetic Hall ribbons, Science 349,1510 (2015).

[4] L. Wang, A. A. Soluyanov, and M. Troyer, Proposal for direct measurement of topological invariants in optical lattices, Phys. Rev.

Lett. 110, 166802 (2013).

135



Probing topology by “heating”

Duc Thanh Tran,1 Alexandre Dauphin,2 Adolfo Grushin,3,4 Peter Zoller,5,6 and Nathan Goldman1

1 Center for Nonlinear Phenomena and Complex Systems, Université Libre de Bruxelles, Belgium2 ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain

3 Department of Physics, University of California, Berkeley, California 94720, USA4 Institut Néel, CNRS and Université Grenoble Alpes, F-38042 Grenoble, France

5 Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria6 Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria

We reveal an intriguing manifestation of topology, which appears in the depletion rate of topologicalstates of matter in response to an external drive [1]. This phenomenon is presented by analyzing theresponse of a generic 2D Chern insulator subjected to a circular time-periodic perturbation: due to thesystem’s chiral nature, the depletion rate is shown to depend on the orientation of the circular shake.Most importantly, taking the difference between the rates obtained from two opposite orientationsof the drive, and integrating over a proper drive-frequency range, provides a direct measure of thetopological Chern number of the populated band (ν): this “differential integrated rate” is directly relatedto the strength of the driving field through the quantized coefficient η0=ν/ħh

2. Contrary to the integerquantum Hall effect, this quantized response is found to be non-linear with respect to the strengthof the driving field and it explicitly involves inter-band transitions. We investigate the possibility ofprobing this phenomenon in ultracold gases and highlight the crucial role played by edge states inthis effect. We extend our results to 3D lattices, establishing a link between depletion rates and thenon-linear photogalvanic effect predicted for Weyl semimetals. The quantized effect revealed in thiswork designates depletion-rate measurements as a universal probe for topological order in quantummatter.

[1] D. T. Tran, A. Dauphin, A. G. Grushin, P. Zoller, and N. Goldman, arXiv:1704.01990 (2017).

136



Fermionization and Mott insulator formation in few-fermion clusters inone-dimensional optical lattices

María Carmen Gordillo and Feliciano De Soto

Universidad Pablo de Olavide

The behavior of small one-dimensional clusters of fermions with repulsive interactions loaded in differentoptical lattices was obtained by means of diffusion Monte Carlo calculations. We observe that, in additionto the limit of infinite interatomic repulsion, we can see fermionization for moderate values of theinterparticle coupling if the lattice potential was deep enough. In addition, for certain values of thelattice-defining parameters, Mott insulators as small as three atoms were found. In all those cases, Mottinsulator formation implies fermionization, but fermionization does not necessarily imply Mott insulatorformation.

137



Unusual transport properties of the 1D Fermi-Hubbard model

Fabian Heidrich-Meisner,1 Christoph Karrasch,2 Tomaz Prosen,3 and Dante Kennes4

1 LMU Munich, Germany2 FU Berlin, Germany

3 University of Ljubljana, Slovenia4 Columbia University, New York, USA

Integrable models such as the spin-1/2 Heisenberg chain, the Lieb-Liniger, or the one-dimensionalHubbard model are known to avoid thermalization, which was also demonstrated in several quantum-quench experiments. Another dramatic consequence of integrability is the zero-frequency anomaly intransport coefficients, which can result in ballistic finite-temperature transport, despite the presenceof strong interactions. Most notably, the Hubbard model is an ideal thermal conductor [1]. Whilethis aspect of nonergodic dynamics has been known for a long time, there has so far not been anyunambiguous experimental realization thereof. We make a concrete proposal for the observation ofballistic transport via local quantum-quench experiments in fermionic quantum-gas microscopes [2].Such an experiment would also unveil the coexistence of ballistic and diffusive transport channels inone and the same system and provide a means of measuring finite-temperature Drude weights. Theconnection between local quenches and linear-response functions is established via time-dependentEinstein relations.

[1] Karrasch, Kennes, Heidrich-Meisner, Phys. Rev. Lett. 117, 116401 (2016).

[2] Karrasch, Prosen, Heidrich-Meisner, Phys. Rev. B 95, 060406(R) (2017).

138



Noncooled site-resolved imaging of a Mott insulator

Ryotaro Inoue, Martin Miranda, Naoki Tambo, and Mikio Kozuma

Tokyo Institute of Technology

We will report on site-resolved imaging of Yb-174 on a two-dimensional optical lattice without relyingon laser-cooling techniques during fluorescence imaging [1]. The formation of Mott shells has beensuccessfully observed by the noncooling approach. Loss and hopping probabilities during our 40-µs-longimaging period are estimated as 1.8% for the loss and less than 0.7% for the hopping. The site-resolvedimaging provides us with a sensitive thermometer; resulting entropy per atom of 0.3kB has beenachieved. We will also report on the observation of SU(6) Mott insulator of fermionic Yb-173 withoutany modification in the imaging setup.

[1] M. Miranda, R. Inoue, N. Tambo, and M. Kozuma, arXiv:1704.07060 (2017).

139



One-dimensional spinor Bose gases: Magnetic order and non-equilibriumdynamics

Karina Jiménez García, Andrea Invernizzi, Camille Frapolli, Bertrand Evrard, Jean Dalibard, andFabrice Gerbier

Laboratoire Kastler Brossel, Collège de France, CNRS, ENS-PSL Research University, UPMC-Sorbonne Universités, 11 place Marcelin

Berthelot, 75005 Paris, France

Spinor Bose gases—bosonic quantum systems with internal degree of freedom s—are excellent candidatesto investigate the underlying physical mechanisms behind magnetic order. While ferromagnetism isfavored in systems with s = 1/2, atomic quantum gases with s > 1/2 can support more complex magneticphases, such as spin-nematics.Spinor Bose gases in reduced dimensions are particularly interesting to study both the spatial organizationof spins in equilibrium, as well as non-equilibrium dynamics after a quench across a magnetic quantumphase transition.Here we present the experimental study of one-dimensional s = 1 Bose gases of Na atoms across amagnetic quantum phase transition. We observe phase separation and the formation of spin domainspurely driven by antiferromagnetic spin-exchange interactions. We measure a 60-fold increase of thelinear response to a magnetic field gradient—the so-called spin-dipole polarizability—for a partiallypolarized and phase-separated spinor gas compared to a completely polarized system. Finally, wediscuss experimental progress toward the observation of the non-equilibrium formation and coarseningdynamics of spin domains.

140



Three-body physics with finite-range potentials

Paul Mestrom, Thomas Secker, and Servaas Kokkelmans

Eindhoven University of Technology

Three-body Efimov physics is relevant for the understanding of both dynamics and stability of ultracoldgases. Efimov predicted the existence of an infinite sequence of three-body bound states, of whichmany properties scale universally, at diverging scattering length for a zero-range interaction potential.Experiments with ultracold atoms in which the scattering length is tuned through Feshbach resonanceshave also shown that the three-body parameter is universally linked to the finite-range of the two-bodyinteraction potential. For small scattering lengths non-universal features appear in the Efimov spectrum,which are also linked to the finite-range nature of the interactions. We consider the full non-separableoff-shell two-body T-matrix which is present in the three-body Faddeev equations and analyze thecorresponding separable expansions. This momentum space treatment allows us, for instance, to showthat strong d-wave interactions lower the energy of the second Efimov state making it possible to preventthis Efimov state from merging with the atom-dimer threshold. We also show that calculations of thethree-body parameter corresponding to the potential resonances of deep square well potentials requiremany terms in the expansion the off-shell two-body T-matrix.

141



Breaking integrability in a dipolar quantum Newton’s cradle

Benjamin Lev

Stanford University

The manner in which integrable quantum systems thermalize when subjected to a weak integrabilitybreaking perturbation remains a mystery. Does the system immediately become quantum chaotic, or doesit retain some memory of integrability in its dynamics? If the latter, how weak must the perturbation befor such near-integrable dynamics to persist? We present an experiment that explores these questions ina strongly interacting system. Dipolar gases of dysprosium are confined in one-dimensional traps. Whilea short-range interacting 1D gas is an integrable system, the dipolar interaction can break integrability.The angle of the magnetic dipole moments with respect to the tube axis controls the strength of theintegrability-breaking perturbation. Our results shed light on the longstanding question of the existenceand nature of a quantum analog to the classical KAM theorem.

142



Bose polarons

Jesper Levinsen,1 Meera Parish,1 Shimpei Endo,1 Shuhei Yoshida,1,2 and Georg Bruun3

1 Monash University2 University of Tokyo3 Aarhus University

The problem of an impurity particle moving through a bosonic medium is of fundamental importancein physics. This quasiparticle, the so-called Bose polaron, was recently observed in two cold-atomexperiments [1,2] using radio frequency spectroscopy on impurity atoms in Bose-Einstein condensates.Both experiments observed well-defined quasiparticles, even for unitary interactions. Here I discussthe theoretical approach introduced in [1,3] to model the radio frequency response. This is basedon truncating the Hilbert space of impurity wave functions at 2 excitations of the BEC. I also presentrecent predictions for light impurities in a BEC, where we expect a strong coupling between many-bodyand Efimov physics, and for static impurities immersed in a BEC which display a surprisingly strongdependence on details of the interactions.

[1] Jørgensen, Wacker, Skalmstang, Parish, Levinsen, Christensen, Bruun, and Arlt, Observation of attractive and repulsive polarons

in a Bose-Einstein condensate, Phys. Rev. Lett. 117, 055302 (2016).

[2] M.-G. Hu, Van de Graaff, Kedar, Corson, Cornell, and Jin, Bose polarons in the strongly interacting regime, Phys. Rev. Lett. 117,

055301 (2016).

[3] Parish and Levinsen, Quantum dynamics of impurities coupled to a Fermi sea, Phys. Rev. B 94, 184303 (2016).

143



Simulating condensed matter with ultracold atoms: The Haldane model andthe Peierls substitution

Michele Modugno1,2

1 Ikerbasque2 Department of Theoretical Physics, University of the Basque Country UPV/EHU

The Haldane model is a celebrated two-dimensional tight-binding model characterized by a quantumHall effect due to the breaking of time-reversal symmetry, with zero net magnetic flux through the unitcell [1]. It is characterized by exotic quantum phases with different Chern numbers, depending onthe value of the phase of the next-to-nearest tunneling amplitude. In its original formulation [1], themodel is constructed by means of the so-called Peierls substitution (PS) [2,3], a popular approach that iswidely employed in the literature to account for the effect of a vector gauge field A in the tight-bindingdescription of electrons, as well as for ultracold atoms in optical lattices in the presence of artificialgauge fields. In the tight-binding language, it amounts to adding to the "bare" tunneling coefficients aphase factor proportional to the line integral of A. Despite its popularity, the PS is a rather uncontrolledapproximation. Though this has been remarked from time to time in the literature [6,7], the generaltendency is to use the PS as a sort of minimal coupling for tight-binding models, and this can lead tosevere failures.In a recent work [8], we have pointed out that the conditions for the applicability of the PS are explicitlyviolated in the Haldane model and in any other model where the vector potential varies on the samescale of the underlying lattice. Nonetheless, we have shown that the general structure of the Haldanemodel is in fact preserved, as it is a direct consequence of the symmetries of the system, and no additionalassumptions are required. In addition, we have shown that the values of the tunneling coefficientscan be obtained from simple closed expressions in terms of gauge invariant, measurable propertiesof the spectrum (namely, the gap at the Dirac point and the bandwidths). These formulas evidencethat the phase acquired by the next-to-nearest tunneling amplitude is quantitatively different from thatpredicted by the PS, and it also presents a pronounced dependence on the intensity of the underlyinglattice potential. Moreover, even the tunneling amplitudes turn out to be dependent on the intensityof A, violating the hypotheses behind the PS. These results have been also checked against ab-initiocalculations by means of the maximally localized Wannier functions (MLWFs) [9], which are also helpfulin understanding the origin of the breakdown of the PS.

[1] F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988).

[2] D. R. Hofstadter, Phys. Rev. B 14, 2239 (1976).

[3] B. A. Bernevig, Topological Insulators and Topological Superconductors (Princeton University Press, 2013).

[4] M. Graf and P. Vogl, Phys. Rev. B 51, 4940 (1995).

[5] T. B. Boykin, R. C. Bowen, and G. Klimeck, Phys. Rev. B 63, 245314 (2001).

[6] W. Kohn, Phys. Rev. 115, 1460 (1959).

[7] A. S. Alexandrov and H. Capellmann, Phys. Rev. Lett. 66, 365 (1991); Z. Phys. B 83, 237 (1991).

[8] J. Ibanez-Azpiroz, A. Eiguren, A. Bergara, G. Pettini, and M. Modugno, Phys. Rev. A 90, 033609 (2014); J. Ibanez-Azpiroz, A.

Eiguren, A. Bergara, G. Pettini, and M. Modugno, Phys. Rev. B 92, 195132 (2015); M. Modugno, J. Ibanez-Azpiroz, and G. Pettini,

Sci. China-Phys. Mech. Astron. 59, 660001 (2016).

[9] N. Marzari and D. Vanderbilt, Phys. Rev. B 56, 12847 (1997).

144



Dynamics of orbital angular momentum states of ultracold atoms in ringpotentials

Gerard Pelegrí, Joan Polo, Verònica Ahufinger, and Jordi Mompart

Department of Physics. Universitat Autònoma de Barcelona

We first investigate the dynamics of orbital angular momentum states for a single ultracold atom trappedin two-dimensional systems of sided coupled ring potentials [1]. The symmetries of the system showthat tunneling amplitudes between different ring states with variation of the winding number arecomplex. In particular, we demonstrate that in a triangular ring configuration the complex nature of thecross-couplings can be used to geometrically engineer spatial dark states to manipulate the transportof orbital angular momentum states via quantum interference. This triangular trapping configurationmay open a myriad of possibilities when assumed to be the unit cell of a 2D lattice. Then, we addressthe dynamics of a Bose-Einstein condensate in a ring trap formed by an imbalanced superposition ofstates with one unit of orbital angular momentum and positive or negative winding number to use it asa quantum sensing device of two-body interactions, magnetic fields and rotations.

[1] J. Polo, J. Mompart, V. Ahufinger, Phys. Rev. A 93, 033613 (2016).

145



Quantum Galilean cannon as a Schrödinger cat

Maxim Olshanii,1 Thibault Scoquart,2,1 Dmitry Yampolsky,1 Vanja Dunjko,1 and Steven Jackson3

1 Department of Physics, University of Massachusetts Boston, Boston, MA 02125, USA2 Département de Physique, Ecole Normale Supérieure, 24, rue Lhomond, 75005 Paris, France

3 Department of Mathematics, University of Massachusetts Boston, Boston Massachusetts 02125, USA

A quantum Galilean cannon is a 1D sequence of N hard-core particles with special mass ratios, and ahard wall; conservation laws due to the reflection group AN prevent both classical stochastization andquantum diffraction. It is realizable through specie-alternating mutually repulsive bosonic soliton trains.We show that an initial disentangled state can evolve into one where the heavy and light particles areentangled, and propose a sensor, containing Ntotal atoms, with a

p

Ntotal times higher sensitivity than ina one-atom sensor with Ntotal repetitions.

146



Probing superfluidity in a quasi two-dimensional Bose gas through its localdynamics

Camilla De Rossi,1 Romain Dubessy,1 Karina Merloti,1 Mathieu de Goër de Herve,1 Thomas Badr,2

Aurélien Perrin,2 Laurent Longchambon,1 and Hélène Perrin2

1 Université Paris 13, Sorbonne Paris Cité, CNRS, Laboratoire de physique des lasers, F-93430, Villetaneuse, France2 CNRS, UMR 7538, Université Paris 13, Sorbonne Paris Cité, F-93430, Villetaneuse, France

We report direct evidence of superfluidity in a quasi two-dimensional Bose gas by observing its dynamicalresponse to a collective excitation, the scissors mode [1]. Relying on a novel local average analysis,we are able to probe inhomogeneous clouds and reveal their local dynamics. We identify in this waythe superfluid and thermal phases inside the gas and locate the boundary at which the Berezinskii–Kosterlitz–Thouless crossover occurs. This new analysis also allows to evidence the coupling of the twofluids which induces at finite temperatures damping rates larger than the usual Landau damping.

[1] Camilla De Rossi et al., New J. Phys. 18, 062001 (2016).

147



Energy transport in bosonic ladders: Interplay between interactions, gaugefield and geometry of system-bath coupling

Dario Poletti and Chu Guo

Singapore University of Technology and Design

Quantum systems in contact with an environment display a rich physics emerging from the interplaybetween dissipative and Hamiltonian terms. Here we consider a dissipative boundary driven ladderin presence of a gauge field which can be implemented with ion microtraps arrays. We focus on theinterplay between the gauge field and the position of the coupling between the system and the baths.First we analyze the non-interacting case. We show that, depending on the geometry, the gauge fieldcan drive two non-equilibrium phase transitions. In the different phases both the magnitude of thecurrent and its spatial distribution are significantly different. Strong interactions significantly suppressthe dependence of the current with the magnetic field and they result also in negative differentialconductivity.

[1] C. Guo and D. Poletti, Phys. Rev. A 94, 033610 (2016).

[2] C. Guo and D. Poletti, manuscript in preparation (2017).

148



Quantum simulation of mesoscopic Fermi systems

Philipp Preiss, Andrea Bergschneider, Vincent Klinkhamer, Justin Niedermeyer, Jan Hendrik Becher,Gerhard Zuern, and Selim Jochim

Heidelberg University, Germany

Ultracold quantum gases in optical potentials have achieved spectacular progress in the experimentalsimulation of complex quantum systems. Complementary to many-body experiments, mesoscopicsystems comprised of a small number of atoms offer the possibility to study entangled quantum stateswith an exceptional degree of versatility and control. We have implemented a highly tunable platform tostudy such correlated few-fermion systems. Using reconfigurable optical microtraps, we prepare quantumstates of 6Li atoms with a deterministic atom number and spin configuration and tune interactions viaa magnetic Feshbach resonance. A novel readout scheme with single-particle sensitivity allows us tomeasure spin-resolved momentum correlation functions. Such correlators characterize few-body systemsvia the coherence and symmetry of the wavefunction. Focusing on the Fermi-Hubbard double-well, weobserve high-contrast interference of indistinguishable fermions, the build-up of correlations due tointeractions, and the emergence of entanglement between particles. Our techniques can be appliedto larger systems to characterize many-body phases via their high-order correlation functions and areparticularly suited to observe the emergence of Cooper pairing in Fermi gases.

149



A precision quantum sensor based on free falling Bose-Einstein condensates

Nick Robins

Department of Quantum Science, Australian National University

A Bose-Einstein condensate is used as an atomic source for a high precision sensor. A 5×106 atom F = 1spinor condensate of 87Rb is released into free fall for up to 750 ms and probed with a T = 130 ms Mach-Zehnder atom interferometer based on Bragg transitions. The Bragg interferometer simultaneouslyaddresses the three magnetic states m f = 1,0,−1, facilitating a simultaneous measurement of theacceleration due to gravity with a 1000 run precision of ∆g/g = 1.45× 10−9 and the magnetic fieldgradient to a precision of 120 pT/m. Offsetting the final interferometer pulse by 300 µs leads tospatial fringes on the output states of the MZ interferometer, potentially offering new measurementopportunities.

[1] PRL 117, 138501 (2016).

150



Studying quantum criticality with quantum observables in cold-atomexperiments

Tommaso Roscilde and Irénée Frérot

Laboratoire de Physique, ENS de Lyon

Quantum many-body states possess features that have no classical analog, and that are genericallystemming from the superposition principle in quantum mechanics. Extracting unambiguous signaturesof quantum superposition necessarily amounts to probing genuinely quantum observables—namelyproperties which are identically zero (hence meaningless) in classical systems. This program is clearlyarduous in real-life situations, as it requires to differentiate firmly between quantum (coherent) superpo-sitions and classical (incoherent) superpositions (namely statistical ensemble properties). Here we shallillustrate theoretically that a rich diagnostics (based alternatively on thermodynamic measurements,quantum gas microscopy or on spectroscopy - bulk or local) can be used to extract the amplitudeof quantum-coherent fluctuations (the so-called “quantum variance”) of observables in cold-atom ex-periments. Quantum fluctuations are dramatically enhanced—and acquire universal critical scalingforms—in the finite-temperature “critical fan” emanating from quantum critical points. Hence theyenable the characterisation of quantum criticality in the most literal sense, namely as the manifestationof critical behaviour of genuinely quantum observables. We shall illustrate this aspect in case of thequantum Ising transition, realised in the the cold-atom context via the mixing-demixing transition of alattice binary mixture.

[1] I. Frérot and T. Roscilde, Phys. Rev. B 94, 075121 (2016); D. Malpetti and T. Roscilde, Phys. Rev. Lett. 117, 130401 (2016).

151



Experimental characterization of a quantum many-body system viahigher-order correlations

T. Schweigler,1 V. Kasper,2 S. Erne,1,2 I. Mazets,1,3 B. Rauer,1 F. Cataldini,1 T. Langen,1,4 T. Gasenzer,5 J.Berges,2 and J. Schmiedmayer1

1 Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Vienna, Austria2 Institut fuür Theoretische Physik, Universität Heidelberg, Heidelberg, Germany

3 Wolfgang Pauli Institute, 1090 Vienna, Austria4 Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany

5 Kirchhoff-Institut fuür Physik, Universität Heidelberg, Heidelberg, Germany

Quantum systems can be characterized by their correlations. Higher-order (larger than second order)correlations, and the ways in which they can be decomposed into correlations of lower order, provideimportant information about the system, its structure, its interactions and its complexity. The measure-ment of such correlation functions is therefore an essential tool for reading, verifying and characterizingquantum simulations. Although higher-order correlation functions are frequently used in theoreticalcalculations, so far mainly correlations up to second order have been studied experimentally. Here westudy a pair of tunnel-coupled one-dimensional atomic super-fluids and characterize the correspondingquantum many-body problem by measuring correlation functions [1]. We extract phase correlationfunctions up to tenth order from interference patterns and analyse whether, and under what conditions,these functions factorize into correlations of lower order. This analysis characterizes the essential featuresof our system, the relevant quasiparticles, their interactions and topologically distinct vacua. From ourdata we conclude that in thermal equilibrium our system can be seen as a quantum simulator of thesine-Gordon model, relevant for diverse disciplines ranging from particle physics to condensed matter.The measurement and evaluation of higher-order correlation functions can easily be generalized toother systems and to study correlations of any other observable such as density, spin and magnetization.It therefore represents a general method for analysing quantum many-body systems from experimentaldata.

Supported by the DFG/FWF: SFB ISOQUANT and the EU through the ERC-AdG QuantumRelax

[1] T. Schweigler et al., Nature 545, 323 (2017).

152



An optical quasicrystal for ultracold atoms

Ulrich Schneider


Ultracold atoms in optical lattices have emerged as a powerful model system to study the many-bodyphysics of interacting particles in periodic potentials. The main objective of our experiment is to extendthis level of control to quasiperiodic potentials by realizing an optical quasicrystal. Quasicrystals area novel form of condensed matter that is non-periodic, but long-range ordered. They have first beenobserved in the 1980s by Dan Shechtman using diffraction experiments. Quasicrystals give rise to adiffraction pattern of sharp Bragg peaks, similar to periodic crystals, but with rotational symmetriesthat are forbidden for periodic structures. Their structure was found to be described by aperiodictilings with more than one unit cell, similar to the celebrated Penrose tiling. Even though quasicrystalsare long-range ordered, many foundational concepts of periodic condensed matter systems such asBlochwaves or Brillouin zones are not applicable. This places them on an interesting middle groundbetween periodic and disordered systems and highlights their potential for novel many-body physics. Inparticular, we expect novel transport phenomena, likely related to many-body localization, as well asan intriguing link to higher-dimensional physics: a 2D quasicrystal can be derived from a periodic 4D“parent” crystal using the cut-and-project method, inheriting the edge states and topological propertiesof the parent. These highly frustrated systems might furthermore contain interesting novel phases atstrong interactions. Our apparatus is almost completed; we have obtained a 87Rb BEC at the end ofApril, and will likely be able to present first lattice experiments.

153



Quantum liquid droplets in a Bose-Bose mixture of ultracold atoms

Giulia Semeghini,1,2 Giovanni Ferioli,1 Leonardo Masi,1 Chiara Mazzinghi,1 Francesco Minardi,2

Giovanni Modugno,1 Michele Modugno,3,4 Massimo Inguscio,2 and Marco Fattori1,2

1 LENS and Dipartimento di Fisica e Astronomia, Università di Firenze, Via N. Carrara 1, 50019, Sesto Fiorentino, Italy2 CNR-INO, Via N. Carrara 1, 50019, Sesto Fiorentino, Italy

3 Depto. de Fìsica Teòrica e Hist. de la Ciencia, Universidad del Pais Vasco UPV/EHU, 48080 Bilbao, Spain4 IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

Ultracold atomic systems are commonly found in a gas phase. Recent theoretical and experimental results[1-3] have surpringly pointed out that under special circumstances condensed atoms can form self-boundliquid-like droplets. At the origin of this new phase is the coexistence of repulsive and attractive forcesthat perfectly balance to generate the self-binding mechanism. In a condensed Bose-Bose mixture thetwo competing energies are provided by the mean-field (MF) interaction and the first beyond mean-fieldcorrection, the so-called Lee-Huang-Yang (LHY) term. When the attraction between the two atomicspecies becomes larger than the average repulsion in the single species, the condensate is expected tocollapse according to MF theory. In this regime, instead, the positive LHY contribution arises to arrestcollapse and stabilize the system [1]. In our experiment we first observe the existence of such self-boundensembles in a bosonic mixture of 39K atoms and we characterize their equilibrium properties. Differentlyfrom their analogue in dipolar systems [2,3], quantum droplets realized with bosonic mixtures arepredicted to be macroscopic zero-temperature objects, due to their peculiar energy spectrum, where nodiscrete modes are expected below the particle emission threshold. The first observation reported inthis work certainly opens the way to further studies of the exotic properties of this new phase, whichalso constitutes the only known quantum liquid together with helium nanodroplets.

[1] D. S. Petrov, Phys. Rev. Lett. 115, 155302 (2015).

[2] M. Schmitt et al., Nature 539, 259 (2016).

[3] L. Chomaz et al., Phys. Rev. X 6, 041039 (2016).

154



Cavity-induced generation of non-trivial topological states inquasi-one-dimensional and two-dimensional Fermi gas

Ameneh Sheikhan,1 Stefan Wolff,1 Ferdinand Brennecke,2 and Corinna Kollath1

1 HISKP, University of Bonn, Nussallee 14-16, 53115 Bonn, Germany2 Physikalisches Institut, University of Bonn, Wegelerstr. 8, 53115 Bonn, Germany

We propose how topologically non-trivial states can dynamically organize in a fermionic quantum gascoupled to the field of an optical cavity. The atoms are confined to either a two-dimensional opticallattice potential or a ladder geometry. The spontaneously emerging cavity field induces together withcoherent pump laser fields a dynamical gauge field for the atoms. In two dimension, upon adiabaticelimination of the cavity degree of freedom, the system is described by an effective Hofstadter modelwith a self-consistency condition which determines the tunneling amplitude along the cavity direction.The fermions are found to self- organize into topologically non-trivial states which carry an extendededge state for a finite system size. Due to the dissipative nature of the cavity field, the topological steadystates are protected from external perturbations. When atoms are confined in a quasi-one-dimensionallattice a chiral current is dynamically stabilized by the feedback mechanism with the cavity field.

[1] A. Sheikhan, F. Brennecke, and C. Kollath, Cavity-induced generation of non-trivial topological states in a two-dimensional Fermi

gas, Phys. Rev. A 94, 061603(R) (2016).

[2] S. Wolff, A. Sheikhan, and C. Kollath, Dissipative time evolution of a chiral state after a quantum quench, Phys. Rev. A 94,

043609 (2016).

[3] A. Sheikhan, F. Brennecke, and C. Kollath, Cavity-induced chiral states of fermionic quantum gases, Phys. Rev. A 93, 043609

(2016).

[4] C. Kollath, A. Sheikhan, S. Wolff, and F. Brennecke, Ultracold fermions in a cavity-induced artificial magnetic field, Phys. Rev.

Lett. 116, 060401 (2016).

155



Two-dimensional finite-temperature bosonic atoms in disorder

Georgy Shlyapnikov

CNRS, LPTMS

We study phase transitions in a two-dimensional weakly interacting Bose gas in a random potentialat finite temperatures. We identify superfluid, normal fluid, and insulator phases and construct thephase diagram. At zero temperature one has a tricritical point where the three phases merge. In thethermodynamic limit the insulator phase does not exist at temperatures above a certain critical value,and at lower temperatures all phase transitions occur when the interaction energy per particle is of theorder of the characteristic disorder energy.

156



AC conductivity measurement of ultracold fermions in an optical lattice

Rhys Anderson,1 Fudong Wang,1 Peihang Xu,1 Vijin Venu,1 Stefan Trotzky,1 Frederic Chevy,2 AntoineGeorges,3 Shizhong Zhang,4 and Joseph Thywissen1

1 University of Toronto2 Laboratoire Kastler Brossel, ENS Paris

3 Collège de France4 Hong Kong University

We measure the global conductivity of neutral atoms in a cubic lattice. As proposed by [1-3], this isdone by applying a time-varying force and observing the resulting current in the linear response regime.At each probe frequency, the response is a complex tensor, and analogous to “optical conductivity”commonly measured in materials with optical reflection or THz radiation. From such measurements,one learns about the carrier density, the symmetry axes of the material, the Hall conductivity, and thetransport time. We present data for various lattice depths and interaction strengths. We discuss exactrelations such as the f-sum rule, compare to several models for AC conductivity, and discuss the relationto transient global response.

[1] A. Tokuno and T. Giamarchi, PRL 106, 205301 (2011).

[2] Z. Wu and E. Zaremba, Annals of Physics 342, 214 (2014).

[3] Z. Wu, E. Taylor, and E. Zaremba, EPL 110, 26002 (2015).

157



Anomalous transport in attractively interacting Fermi gases

Shun Uchino1 and Masahito Ueda1,2

1 Center for Emergent Matter Science, RIKEN2 Department of Physics, the University of Tokyo

Attractively interacting Fermi gases realized in ultracold atoms have attracted attention due to connec-tions to neutron stars and high-temperature superconductors. A new aspect of studies in such systemsis to understand the nonequilibrium properties through transport that have been examined with atwo-terminal setup realized by the Tilman Esslinger’s group at ETH. In this presentation, we discusstransport properties of the attractively interacting Fermi gases through a quantum point contact. In theabsence of interaction, it is known that the conductance quantization known as the Landauer-Buttikerformula is obtained. However, in the presence of interaction, we show that near the superfluid transitiontemperature, the conductance can be significantly enhanced by superfluid fluctuations. There, transportof fluctuation (preformed) pairs is essential, which has been overlooked in previous studies. Our resultsare consistent with the experimental observations [1].

[1] Shun Uchino and Masahito Ueda, Phys. Rev. Lett. 118, 105303 (2017).

158



Rydberg excitation and Rydberg dressing of ultracold gases on an atom chip

Klaasjan van Druten,1 Nataly Cisternas,1 Julius de Hond,1 Graham Lochead,1 Severin Charpignon,1 Ben

van Linden van den Heuvell,1 Robert Spreeuw,1 Marcin Plodzien,2 and Servaas Kokkelmans2

1 University of Amsterdam2 Eindhoven University of Technology

Atom chips offer unique opportunities to study quantum-degenerate gases. In particular, it is straightfor-ward to produce highly elongated and one-dimensional Bose-Einstein condensates. One of the challengesis to create tuneable interactions, in particular because magnetic trapping is incompatible with the usualmagnetic tuning to a Feshbach resonance. An appealing approach is to instead use Rydberg-mediatedinteractions such as Rydberg dressing to create strong, long-range, tuneable and switchable interactions.An important issue is the presence of stray electric fields near the surface of the atom chip. In theexperiments, the sensitive response to electric fields of Rydberg atoms has been used to characterise allthree vector components of the local electric field. The strength of these electric fields is modest andit seems promising to explore the opportunities for Rydberg-mediated interactions in our system. Anext-generation chip design that allows compensating the stray electric fields will also be presented.The possibilities of Rydberg dressing of one-dimensional Bose-Einstein condensates in our system hasalso been analysed [1], and this appears more promising than a three-dimensional geometry.

[1] M. Plodzien et al., Rydberg dressing of a one-dimensional Bose-Einstein condensate, Phys Rev. A 95, 043606 (2017).

159



Mean field and beyond mean field spin mixing dynamics in Chromium quantumgases

Steven Lepoutre,1,2 Kaci Kechadi,1,2 Bruno Naylor,1,2 Bihui Zhu,3 Johannes Schachenmayer,3 LucasGabardos,1,2 Paolo Pedri,1,2 Ana Maria Rey,3 Laurent Vernac,1,2 and Bruno Laburthe-Tolra1,2

1 Université Paris 13, Sorbonne Paris Cité, Laboratoire de Physique des Lasers, F-93430, Villetaneuse, France2 CNRS, UMR 7538, LPL, F-93430, Villetaneuse, France

3 JILA, NIST and Department of Physics, University of Colorado, Boulder, USA

We experimentally study spin mixing dynamics in spin 3 chromium quantum Bose gases, in bulk orlattices. We initiate dynamics by tilting the spins by an angle θ with respect to the external magneticfield. We show that in the superfluid regime persistence of locally fully magnetized classical statesdisfavours beyond mean field physics. In contrast, in the Mott regime, the pure dipolar spin dynamicshas a beyond mean field character. In the BEC case, dynamics is induced by the interplay betweenlong-range dipolar and short-range contact exchange interactions. While spin mixing is triggered bydipolar coupling, it is strongly influenced by contact interactions once started. For the particular caseθ = π/2, an external spin-orbit coupling term, induced by a magnetic gradient, is required to drivethe spin dynamics. In that case, relatively strong spin-dependent contact interactions tend to locallypreserve ferromagnetism. In a deep 3D lattice, with one atom per site, only intersite dipolar interactionsare at play. While a mean field approach fails to reproduce the data, we obtain good agreement withsimulations based on the Truncated Wigner Approximation, which indicates the emergence of quantumcorrelations.

160



Controlled summation of diagrammatic series for the unitary Fermi gas: Bolddiagrammatic Monte Carlo, large-order asymptotics and conformal-Borel

transformation

Riccardo Rossi,1 Takahiro Ohgoe,2 Kris Van Houcke,1 and Félix Werner3

1 Laboratoire de Physique Statistique, Ecole Normale Supérieure2 University of Tokyo

3 Laboratoire Kastler Brossel, Ecole Normale Supérieure

We consider the unitary Fermi gas (spin 1/2 fermions with contact interactions in 3D, which describescold atomic gases at a Feshbach resonance) in the normal phase. Thanks to a diagrammatic MonteCarlo algorithm, we accurately sample all skeleton diagrams (built on dressed single-particle and pairpropagators) up to order ≈ 8 [1]. The diagrammatic series is divergent and there is no small parameterso that a resummation method is needed. Previously we used Abelian resummation methods, which areapplicable under the assumption that the diagrammatic series has a non-zero radius of convergence; thisled to good agreement with experimental data for the equation of state [2] and Tan’s contact coefficient[3]. Here we compute the large-order asymptotics of the diagrammatic series, based on a functionalintegral representation of the skeleton series [4] and the saddle-point method. We find that the radiusof convergence is actually zero, and our new numerical results and analytical arguments show that theseries is resummable by an generalised conformal-Borel transformation that incorporates the large-orderasymptotics. This demonstrates that one can obtain controlled results for a strongly correlated fermionicfield theory based on diagrammatic series with zero convergence radius.

[1] K. Van Houcke, F. Werner, N. Prokof’ev, and B. Svistunov, Bold diagrammatic Monte Carlo for the resonant Fermi gas,

arXiv:1305.3901 (2013).

[2] K. Van Houcke, F. Werner, E. Kozik, N. Prokof’ev, B. Svistunov, M. Ku, A. Sommer, L. Cheuk, A. Schirotzek, and M. Zwierlein,

Feynman diagrams versus Fermi-gas Feynman emulator, Nature Phys. 8, 366 (2012).

[3] K. Van Houcke, F. Werner, E. Kozik, N. Prokof’ev, and B. Svistunov, Contact and momentum distribution of the unitary Fermi gas

by bold diagrammatic Monte Carlo, arXiv:1303.6245 (2013).

[4] R. Rossi, F. Werner, N. Prokof’ev, and B. Svistunov, Shifted-action expansion and applicability of dressed diagrammatic schemes,

Phys. Rev. B 93, 161102(R) (2016).

161



A quantum gas microscope of two-electron atoms with fluorescence andFaraday imaging

Ryuta Yamamoto,1,4 Jun Kobayashi,1 Kohei Kato,2 Takuma Kuno,1 Shuya Yamanaka,1 Yoshiki Amano,1

Shinichi Sunami,1 Chae Eunmi,3 Yutaro Suzuki,1 and Yoshiro Takahashi1

1 Department of Physics, Graduate School of Science, Kyoto University2 Department of Physics, Osaka City University

3 Photon Science Center, Graduate School of Engineering, The University of Tokyo4 Present address: RIKEN Center for Emergent Matter Science

Single-site resolved imaging and single-site addressing in a two-dimensional optical lattice (QuantumGas Microscope, QGM) are realized with alkali metals [1] and enable us to directly observe the in-trapatom distribution and study quantum dynamics with single-site resolution. It is important to extend theapplicability of a QGM technique to two-electron atoms such as alkaline-earth metals and ytterbiumatoms because it opens up many unique possibilities for quantum simulation and quantum informationresearch [2]. As compared with the first report on single-site resolved imaging of ytterbium atoms[3], we successfully realize the QGM of ytterbium atoms with about twice shorter lattice constant(266 nm) and much longer lifetime (above 7 s) using narrow-line laser cooling [4]. Moreover, wesuccessfully demonstrate site-resolved imaging with Faraday effect (Faraday QGM) which does notrely on a stochastic spontaneous emission process and the observed Faraday rotation angle reaches3.0(2) degrees for a single atom [5]. Our result is an important first step towards ultimate quantumnon-demolition site-resolved imaging and furthermore opens up the possibility for quantum feedbackcontrol of quantum many-body systems with single-site resolution.

[1] W. S. Bakr et al., Nature 462, 74 (2009); J. F. Sherson et al., Nature 467, 68 (2010).

[2] M. Miranda et al., PRA 91, 063414 (2015).

[3] R. Yamamoto et al., NJP 18, 023016 (2016).

[4] R. Yamamoto et al., arXiv:1607.07045 (2016).

162



Many-body localization transition for bosons in optical lattice

Jakub Zakrzewski,1 Dominique Delande,2,1 and Piotr Sierant1

1 Marian Smoluchowski Institute of Physics, Jagiellonian University2 Laboratoire Kastler-Brossel, Ecole Normale Supérieure,

Many body localization of ultra-cold bosons in a 1D optical lattice is discussed for random interactions.Without a disorder a system reduces to single-particle physics thus the observed localization is inherentlydue to interactions and is a genuine many-body effect. MBL manifests itself in a lack of thermalizationvisible in temporal propagation of a density wave initial state, in the logarithmic growth of entanglemententropy as well as in statistical properties of levels. We extend the results reported in [1] by revealingthe mobility edge in the system via studies of level statistics for different energy intervals. Interestinglythis mobility edge has a “reverse” character with higher lying in energy states being easier to localize.The existence of the mobility edge is also verified directly via studies of dynamics for large system sizes.We investigate the character of MBL-extended states transition. We study also the more standard case ofdisorder in the chemical potential discussing differences and similarities between the two models as wellas the often, also experimentally, studied the case of fermions. Both truly random and quasi-randomdisorder are considered.

[1] Piotr Sierant, Dominique Delande, and Jakub Zakrzewski, Many-body localization due to random interactions, Phys. Rev. A 95,

021601(R) (2017).

163



Deep inelastic scattering on ultracold atoms

Johannes Hofmann1 and Wilhelm Zwerger2

1 DAMPT Cambridge UK2 TU Munich

We discuss Bragg scattering on both Bose and Fermi gases with strong short-range interactions in thedeep inelastic regime of large wave vector transfer q. Using a systematic short-distance expansion,the structure factor at high momentum is shown to exhibit a nontrivial dependence on frequencycharacterized by two separate scaling regimes. First, for frequencies that differ from the single-particleenergy by terms of order O (q), the dynamic structure factor is described by the impulse approximationof Hohenberg and Platzman. Second, deviations of order O (q2) are described by the operator productexpansion, with a universal crossover connecting both regimes. The scaling is consistent with the leadingasymptotics for a number of sum rules in the large momentum limit. Furthermore, we derive an exactexpression for the shift and width of the single-particle peak at large momentum due to interactionswhich extends a result by Beliaev for the low-density Bose gas to arbitrary values of the scatteringlength a. The shift exhibits a maximum around qa ' 1, which is connected with a maximum in thestatic structure factor due to strong short-range correlations. For Bose gases with moderate interactionstrengths, the theoretically predicted shift is consistent with the value observed by Papp et al. at JILA in2008. Finally, we develop a diagrammatic theory for the dynamic structure factor which accounts forthe correlations beyond Bogoliubov theory. It covers the full range of momenta and frequencies andprovides an explicit example for the emergence of asymptotic scaling at large momentum.

[1] PRX 2017.

164



Ultradilute low-dimensional liquids

Grigory Astrakharchik1 and Dmitry Petrov2

1 Departament de Física, Campus Nord B4-B5, Universitat Politecnica de Catalunya, E-08034 Barcelona, Spain2 LPTMS, CNRS, Univ. Paris Sud, Université Paris-Saclay, 91405 Orsay, France

We calculate the energy of one- and two-dimensional weakly-interacting Bose-Bose mixtures analyticallyin the Bogoliubov approximation and by using the diffusion Monte Carlo technique. We show that in thecase of attractive inter- and repulsive intraspecies interactions the energy per particle has a minimumat a finite density corresponding to a liquid state. We derive the Gross-Pitaevskii equation to describedroplets of such liquids and solve it analytically in the one-dimensional case.

165



Dark solitons and vortices in confined superfluids

Joachim Brand, Lauri Toikka, and Antonio Mateo Muñoz

Dodd Walls Centre for Photonic and Quantum Technology, New Zealand Institute for Advanced Study, Centre for Theoretical

Chemistry and Physics, Massey University, Auckland, New Zealand

Even though solitons represent the quintessence of stability among nonlinear wave phenomena, darksolitons are known to suffer the snaking instability in two- or three-dimensional settings. Confinementpotentials typically present in quantum gas experiments strongly influence the decay dynamics of darksolitons [1] and give rise to a family of solitary wave solutions with vortex line structure known asChladni solitons [2]. The simplest, stable, and long-lived member of this family is the solitonic vortex[3,4,5]. We argue that the solitonic vortex could be used as a tool for precise measurement of the vortexmass to reveal features of vortex dynamics, including possibly exotic vortex forces that depend on themicroscopic nature of the superfluid [6].

[1] A. Muñoz Mateo and J. Brand, Stability and dispersion relations of three-dimensional solitary waves in trapped Bose–Einstein

condensates, New J. Phys. 17, 125013 (2015).

[2] A. Muñoz Mateo and J. Brand, Chladni solitons and the onset of the snaking instability for dark solitons in confined superfluids,

Phys. Rev. Lett. 113, 255302 (2014).

[3] J. Brand and W. P. Reinhardt, Solitonic vortices and the fundamental modes of the “snake instability”: Possibility of observation in

the gaseous Bose–Einstein condensate, Phys. Rev. A. 65, 043612 (2002).

[4] M. J. H. Ku, W. Ji, B. Mukherjee, E. Guardado-Sanchez, L. W. Cheuk, T. Yefsah, and M. W. Zwierlein, Motion of a solitonic vortex

in the BEC-BCS crossover, Phys. Rev. Lett. 113, 065301 (2014).

[5] S. Komineas and N. Papanicolaou, Solitons, solitonic vortices, and vortex rings in a confined Bose-Einstein condensate, Phys. Rev.

A. 68, 043617 (2003).

[6] L. A. Toikka and J. Brand, Asymptotically solvable model for a solitonic vortex in a compressible superfluid, New J. Phys. 19,

23029 (2017).

166



Quantum coherent transport of cold fermions in mesoscopic structures

Samuel Hausler,1 Martin Lebrat,1 Dominik Husmann,1 Sebastian Krinner,1 Tilman Esslinger,1 ShutaNakajima,2 Jean-Philippe Brantut,3 Pjotrs Grišins,4 and Thierry Giamarchi4

1 Department of Physics, ETH Zurich, 8093 Zurich, Switzerland2 Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

3 Institute of Physics, EPFL, 1015 Lausanne, Switzerland4 Department of Quantum Matter Physics, Université de Genève, CH-1211 Genève, Switzerland

We investigate the transport properties of fermions passing through a one-dimensional quantum wire.The wire is exposed to tailored, microscopic potentials. In a first set of experiments, we realize a scanninggate microscope by projecting a microscopic potential barrier and scanning it across the mesoscopicconductor. This yields spatially resolved informations on the transport processes. We analyse the spatialresolution and precision of the method, and demonstrate direct tunneling through the obstacle. We thenuse the same setup to project several, evenly spaced barriers thereby producing a mesoscopic lattice.Building an increasingly longer lattice, one site after another, we observe and characterize the emergenceof a band insulating phase, demonstrating quantum-coherent transport. We explore the influence ofatom-atom interactions and discover that the insulating state persists as contact interactions are tunedfrom weakly to strongly attractive. For strongly interacting particles, we find qualitative agreementbetween the observations and the predictions of the Tomonaga-Luttinger model.

167



Induced interactions and topological phases in Fermi-Bose mixtures

Georg Bruun,1 Zhigang Wu,1 Jonatan Meldgaard,1 Daniel Suchet,2 and Frédéric Chevy2

1 Aarhus University2 Ecole Normale Supérieure

We show that a 2D spin-polarised Fermi gas immersed in a 3D BEC constitutes a very promising systemto realise topological superfluids both without and with time-reversal symmetry, which have never beenobserved before. The fermions attract each other via an induced interaction mediated by the bosons,and both the strength and the range of the induced interaction can be tuned experimentally. UsingBerezinskii-Kosterlitz-Thouless (BKT) theory including retardation effects, we demonstrate that theinteraction can be tuned to make the critical temperature approach the maximum value allowed bygeneral BKT theory. We also show that the induced interaction mediated by the BEC can be detectedunambiguously and probed systematically using a setup consisting of two layers of fermions in a BEC.

[1] Physical Review Letters 117, 245302 (2016).

[2] Physical Review A 94, 063631 (2016).

[3] arXiv:1702.08129 (2017).

168



Creating and controlling superfluid vortex rings in artificial magnetic fields

Rashi Sachdeva, James Schloss, and Thomas Busch

OIST Graduate University, 904-0495 Okinawa, Japan

Artificial gauge fields are versatile tools that allow to influence the dynamics of ultracold atoms in Bose-Einstein condensates. In this work we present a method of artificial gauge field generation stemmingfrom the evanescent fields of the curved surface of an optical nanofiber. The exponential decay of theevanescent fields leads to large gradients in the generalized Rabi frequency and therefore to the presenceof geometric vector and scalar potentials. By solving the two- and three-dimensional Gross-Pitaevskiiequation in the presence of the artificial gauge fields originating from the fundamental HE11 modeof the fiber, we show that vortex rings can be created in a controlled manner. We also calculate themagnetic fields resulting from the higher order HE21, TE01, and TM01 modes and compare them to thefundamental HE11 mode [1]. Due to the versatility of the light fields in the nanofibre, such a system canbe thought of as a highly controllable laboratory for topological excitations in BECs. To explore this, wehave developed a GPU-based code for solving Gross-Pitaevskii equation in full three dimensions and useit to study ground state vortex ring structures and their time evolution.

[1] R. Sachdeva and Th. Busch, Phys. Rev. A 95, 033615 (2017).

169



Thermoelectric transport through an atomic quantum point contact

Laura Corman,1 Dominik Husmann,1 Martin Lebrat,1 Samuel Häusler,1 Jean-Philippe Brantut,2 andTilman Esslinger1

1 Institute for Quantum Electronics, ETHZ, 8093 Zürich, Switzerland2 LQG, EPFL, 1015 Lausanne, Switzerland

Thermoelectricity describes the phenomenon by which a temperature gradient drives transport of energyand particles and vice versa. It is of great technological importance for cooling materials (Peltier effect)or power generation (Seebeck effect), but it is also a fundamental probe of the physics of the medium inwhich the energy and particle currents are created. Experimentally, thermoelectric effects have alreadybeen studied with ultracold fermionic lithium atoms using a two-dimensional constriction for weakinteractions [1]. These effects are affected by the properties of both the constriction and the reservoirs,which we here control in our mesoscopic transport setup to explore new conduction regimes. First, wereduce the dimensionality of the constriction: two temperature imbalanced reservoirs are connectedvia a one to few mode channel, which is similar to the condensed matter quantum point contacts.Second, we can change the reservoirs’ properties by varying the interaction strength to reach the unitaryregime. The evolution of particle and energy currents to a temperature gradient are strongly modifiedcompared to the weakly interacting case, where a transient particle imbalance builds up before relaxing.In the strongly interacting regime, this imbalance persists within experimentally reachable durations,reminiscent of the fountain effect.

[1] J.-P. Brantut et al., Science 342, 713 (2013).

170



Coherent control of ultracold RbCs molecules in an optical trap

Simon Cornish,1 Phil Gregory,1 Jacob Blackmore,1 Elizabeth Bridge,1 Ruth Le Sueur,2 Jeremy Hutson,2

and Jesus Aldegunde3

1 Joint Quantum Centre (JQC) Durham-Newcastle, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK2 Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK

3 Departamento de Quimica Fisica, Universidad de Salamanca, 37008 Salamanca, Spain

The formation of ultracold heteronuclear molecules opens up many exciting areas of research spanningprecision measurement, quantum computation, quantum simulation, ultracold chemistry and fundamen-tal studies of quantum matter. Long-lived, trapped samples of molecules with full quantum control ofthe molecular internal state are crucial to many of these applications. Here we demonstrate coherent mi-crowave control of the rotational and hyperfine state of ultracold, chemically stable 87Rb133Cs molecules.We create up to 4000 molecules in the rovibrational and hyperfine ground state at a temperature of∼ 1.2µK and a density of ∼ 1011 cm−3 using magnetoassociation on a Feshbach resonance [1] followedby optical transfer using stimulated Raman adiabatic passage [2,3]. We then use precision microwavespectroscopy of the rotational transition to probe the rich hyperfine structure of the molecule and exploitcoherent Rabi oscillations to transfer the total population of molecules between hyperfine levels [4]. Wesubsequently investigate the AC Stark effect due to the trapping light in low-lying rotational levels andreveal a rich energy structure with many avoided crossings between hyperfine states. Finally we reportnew measurements of the collisional lifetimes for molecules in various rotational and hyperfine states,shedding light on the “sticky collision” issue [5].

[1] M. P. Köppinger, D. J. McCarron, D. L. Jenkin, P. K. Molony, H.-W. Cho, C. R. Le Sueur, C. L. Blackley, J. M. Hutson and S. L.

Cornish, Production of optically trapped 87RbCs Feshbach molecules, Phys. Rev. A 89, 033604 (2014).

[2] P. K. Molony, P. D. Gregory, Z. Ji, B. Lu, M. P. Köppinger, C. R. Le Sueur, C. L. Blackley, J. M. Hutson, and S. L. Cornish, Creation

of ultracold RbCs molecules in the rovibrational ground state, Phys. Rev. Lett. 113, 255301 (2014).

[3] P. D. Gregory, P. K. Molony, M. P. Köppinger, A. Kumar, Z. Ji, B. Lu, A. L. Marchant and S. L. Cornish, A simple, versatile laser

system for the creation of ultracold ground state molecules, New J. Phys. 17, 055006 (2015).

[4] P. D. Gregory, J. Aldegunde, J. M. Hutson, and S. L. Cornish, Controlling the rotational and hyperfine state of ultracold RbCs

molecules, Phys. Rev. A 94, 041403(R) (2016).

[5] M. Mayle, G. Quéméner, B. P. Ruzic, and J. L. Bohn, Scattering of ultracold molecules in the highly resonant regime, Phys. Rev. A

87, 012709 (2013).

171



New frontiers in the manipulation and probing of ground state polar molecules

Luigi De Marco, Jacob Covey, Kyle Matsuda, William Tobias, Giacomo Valtolina, and Jun Ye

JILA - University of Colorado, Boulder

The production of a quantum gas of ground-state polar molecules is now an experimental reality.Combined with quantum gas microscopy in optical lattices, these systems will provide unheraldedopportunities for exploring many-body physics and especially for emulating spin systems that go beyondnearest-neighbor interactions. In particular, owing to the large molecular electric dipole moment, thelong-range dipole-dipole force allows us to investigate phenomena where the interplay between disorderand interaction strength dominates the system’s dynamics.We present our recent efforts in realizing a new generation apparatus for the production and manipulationof ground state KRb molecules in a three-dimensional optical lattice. With the implementation of invacuum electrodes to achieve tunable electric fields in excess of 30 kV/cm, the intermolecular interactioncan be tuned over a large range of strengths, and various spin Hamiltonians may be realized. Finally,we will describe our proposal for a spin-resolved quantum gas microscope of polar molecules whereinthe molecular spin state is mapped onto an atomic species for detection to provide the greatest insightpossible into the molecules’ quantum dynamics.

172



Dual-degeneracy in a Bose-Fermi mixture with extreme mass imbalance

Brian DeSalvo,1,2,3 Krutik Patel,1,2,3 and Cheng Chin1,2,3

1 The James Franck Institute2 The Enrico Fermi Institute

3 Department of Physics, University of Chicago

We have produced the first quantum degenerate mixture of bosonic 133Cs and fermionic 6Li. Owingto a narrow Feshbach resonance at 892 G, this system offers a flexible platform in which to studystrongly interacting Bose-Fermi mixtures with large mass imbalance. To produce this sample, we firstsequentially laser cool and load each species into separate optical dipole traps. The two species areevaporatively cooled and then combined at ∼ 300 nK in a dual-color optical dipole trap. After a finalstage of evaporative cooling near an inter-species Feshbach resonance, we obtain nearly pure Bose-Einstein condensates of ∼ 2× 104 Cs atoms and T/TF ∼ 0.2 for Li. By tuning the scattering lengthon the attractive side, we reach a novel regime where a small sample of degenerate fermions can betrapped entirely by mean-field interactions with the BEC. Details on this and our search for beyondmean field physics in this exciting system will be discussed.

173



Two- and three-body contacts in the unitary Bose gas

Richard Fletcher,1,2 Raphael Lopes,1 Jay Man,1 Nir Navon,1 Robert Smith,1 Martin Zwierlein,2 andZoran Hadzibabic1

1 University of Cambridge, UK2 Massachusetts Institute of Technology, USA

In many-body systems governed by pairwise contact interactions, a wide range of observables is linkedby a single parameter, the two-body contact, which quantifies two-particle correlations. This profoundinsight has transformed our understanding of strongly interacting Fermi gases. Using Ramsey interfer-ometry, we studied coherent evolution of the resonantly interacting Bose gas, and we show here that itcannot be explained by only pairwise correlations. Our experiments reveal the crucial role of three-bodycorrelations arising from Efimov physics and provide a direct measurement of the associated three-bodycontact.

[1] Science 355, 377 (2017).

174



A transport apparatus for mixed quantum gases with Yb and Rb

Tobias Franzen, Bastian Pollklesener, and Axel Görlitz

University of Düsseldorf

Mixtures of diamagnetic and paramagnetic quantum gases are promising systems for the creation ofensembles of ultracold dipolar molecules which offer interesting prospects for novel interactions inquantum gases, ultracold chemistry, precision measurements and quantum information. Here we reporton a new versatile transport apparatus for the production of ultracold RbYb molecules. This setupconstitutes an improvement of our old apparatus, where the interactions in RbYb and possible routesto molecule production have already been studied extensively [1,2]. In the new setup a major goalis the efficient production of ultracold ground state RbYb molecules. We employ optical tweezers totransport individually cooled samples of ultracold Rb and Yb from their separate production chambersto a dedicated science chamber. In the science chamber, we transfer the atoms to a crossed dipole trap,where further evaporative cooling creates a starting point for the exploration of interspecies interactionsand pathways towards a quantum gas of dipolar ground state molecules.

[1] M. Borkowski et al., PRA 88, 052708 (2013).

[2] C. Bruni et al., PRA 94, 022503 (2016).

175



Observation of antiferromagnetic long-range order in the Hubbard model withultracold atoms

Daniel Greif, Anton Mazurenko, Christie Chiu, Geoffrey Ji, Maxwell Parsons, Marton Kanasz-Nagy,Richard Schmidt, Fabian Grusdt, Eugene Demler, and Markus Greiner

Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

Quantum gas microscopy of ultracold fermionic atoms in optical lattices opens new perspectives foraddressing long-standing open questions on strongly correlated low-temperature phases in the Hubbardmodel. For example, the precise character of the phases emerging when doping an antiferromagnet awayfrom half-filling is still not well understood. We report on the observation of antiferromagnetic long-range order in a repulsively interacting Fermi gas of Li-6 atoms on a 2D square lattice at temperaturesT/t = 0.25. Using single-site resolution, the ordered state is directly detected from a peak in the spinstructure factor and a diverging correlation length of the spin correlation function. In the long-rangeordered state we measure staggered magnetizations exceeding 50% of the ground-state value in thethermodynamic limit. When doping away from half-filling into a numerically intractable regime, wefind that long-range order extends to doping concentrations of about 15%. Our results pave the way fordirectly addressing open questions on pseudo-gap states and high-temperature superconductivity. Wewill also report on our most recent progress towards creating samples with even lower temperaturesand larger system sizes using optimized entropy redistribution schemes.

176



Transport properties of ultracold interacting fermions in a mesoscopic lattice

Martin Lebrat,2 Dominik Husmann,2 Samuel Häusler,2 Laura Corman,2 Jean-Philippe Brantut,2 TilmanEsslinger,2 Pjotrs Grišins,1 and Thierry Giamarchi1

1 University of Geneva2 ETH Zurich

We investigate transport properties of interacting fermions passing through a one-dimensional quantumwire containing a mesoscopic lattice. The lattice is realized by projecting individually controlled opticalbarriers on top of a ballistic conductor. For weakly attractive atoms we observe and characterize theemergence of a band insulating phase, demonstrating quantum-coherent transport. The insulating statepersists even as inter-atomic interaction is tuned from weak to strong, and we find qualitative agreementbetween the observations and the predictions of the Tomonaga-Luttinger model. Our work realizes atunable, site-controlled lattice Fermi gas strongly coupled to reservoirs, which is an ideal test bed fornon-equilibrium many-body physics.

177



Ghost imaging and solving the many-body problem using strongly correlatedatoms from s-wave collision halos

Sean Hodgman,1 Roman Khamimov,1 Bryce Henson,1 David Shin,1 Kenneth Baldwin,1 Robert

Lewis-Swan,2,3 Karen Kheruntsyan,2 and Andrew Truscott1

1 Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia2 University of Queensland, School of Mathematics and Physics, Brisbane, Queensland 4072, Australia

3 JILA, NIST and Department of Physics, University of Colorado, 440 UCB, Boulder, Colorado 80309, USA

Ghost imaging involves two separate correlated beams, one of which passes through an object to asingle-pixel detector, while the spatial profile of a second beam, which never interacts with the object,is recorded on a multi-pixel detector. Using temporal cross-correlations between the two beams, animage of the object is recovered. While ghost imaging has previously been demonstrated with photons,here we realise ghost imaging using atoms [1]. In our experiment, the two beams are formed fromcorrelated pairs of metastable helium atoms created via an s-wave collision between two BECs. Thehighly correlated atom pairs yield a ghost image with sub-millimetre resolution.The s-wave collision halo itself possesses a complex hierarchy of inter-related back-to-back and collinearcorrelation functions. A complete measurement of these correlation functions can be regarded as anoperational solution to the quantum many-body problem for this particular system. We experimentallyshow this by measuring all multi-atom momentum correlation functions between halo atoms up to thirdorder, using a momentum microscope [2]. From these we extract the anomalous density, which alongwith the normal density allows all higher order correlations functions to be reconstructed. We alsodemonstrate a record violation of the Cauchy-Schwarz inequality.

[1] R. I. Khakimov, B. M. Henson, D. K. Shin, S. S. Hodgman, R. G. Dall, K. G. H. Baldwin, and A. G. Truscott, Ghost imaging with

atoms, Nature 540, 100 (2016).

[2] S. S. Hodgman, R. I. Khakimov, R. J. Lewis-Swan, A. G. Truscott, and K. V. Kheruntsyan, Solving the quantum many-body

problem via correlations measured with a momentum microscope, arXiv:1702.03617 (2017).

178



Goldstone mode and pair-breaking excitations in atomic Fermi superfluids

Sascha Hoinka,1 Paul Dyke,1 Marcus G. Lingham,1 Jami J. Kinnunen,2 Georg Bruun,3 and Chris J. Vale1

1 Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne, Australia2 COMP Centre of Excellence, Department of Applied Physics, Aalto University, Aalto, Finland

3 Department of Physics and Astronomy, University of Aarhus, Aarhus, Denmark

We present an experimental and theoretical study of the elementary excitations in a homogeneousstrongly interacting Fermi gas through the crossover from a BCS superfluid to a Bose-Einstein condensateof molecules using low-momentum Bragg spectroscopy. In the long-wavelength regime, Bragg scatteringprobes collective excitations of the gas which are closely linked to the superfluid order parameter. Inour setup, we shine two tightly focussed laser beams into the central, nearly uniform, region of anoptically trapped cloud of lithium-6 atoms to directly measure the homogenous response. The spectraexhibit a discrete Goldstone mode (Bogoliubov-Anderson phonon), associated with the broken symmetrysuperfluid phase, as well as pair breaking single-particle excitations. Our techniques yield a directdetermination of the superfluid pairing gap and speed of sound in close agreement with strong-couplingtheories.We also present our progress towards measuring the temperature dependence of the excitation spectra,below and above the superfluid critical temperature, which may provide insight into the unresolvedquestion of pseudogap pairing in a Fermi gas at unitarity.

179



Superfluid density and critical velocity near the fermionicBerezinskii-Kosterlitz-Thouless transition

Brendan Mulkerin,1 Lianyi He,2 Paul Dyke,1 Chris Vale,1 Xia-Ji Liu,1,3 and Hui Hu1

1 Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia2 State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China

3 Kavli Institute for Theoretical Physics, UC Santa Barbara, USA

We theoretically investigate superfluidity in a strongly interacting Fermi gas confined to two dimensionsat finite temperature. Using a Gaussian pair fluctuation theory in the superfluid phase, we calculatethe superfluid density and determine the critical temperature and chemical potential at the Berezinskii-Kosterlitz-Thouless transition. We propose that the transition can be unambiguously demonstrated incold-atom experiments by stirring the superfluid Fermi gas using a red detuned laser beam, to identifythe characteristic jump in the local Landau critical velocity at the superfluid-normal interface, as thelaser beam moves across the cloud.

[1] B. Mulkerin, L. He, P. Dyke, C. J. Vale, X.-J. Liu, and H. Hu, arXiv:1702.07091 (2017).

180



BCS theory of time-reversal-symmetric Hofstadter-Hubbard model

Menderes Iskin and Onur Umucalilar

Department of Physics, Koç University, Rumelifeneri Yolu, 34450 Sarıyer, Istanbul, Turkey

The competition between the length scales associated with the periodicity of a lattice potential and thecyclotron radius of a uniform magnetic field is known to have dramatic effects on the single-particleproperties of a quantum particle, e.g., the fractal spectrum is known as the Hofstadter butterfly. Havingthis intricate competition in mind, we consider a two-component Fermi gas on a square optical latticewith opposite synthetic magnetic fields for the components, and study its effects on the many-body BCS-pairing phenomenon. By a careful addressing of the distinct superfluid transitions from the semi-metal,quantum spin-Hall insulator or normal phases, we explore the low-temperature phase diagrams of themodel, displaying lobe structures that are reminiscent of the well-known Mott-insulator transitions ofthe Bose-Hubbard model.

[1] Phys. Rev. A 95, 013601 (2017).

181



Momentum distribution and “free” expansion of an anyonic gas

Tena Dubcek,1,2 Bruno Klajn,1 Robert Pezer,3 Hrvoje Buljan,1 and Dario Jukic4

1 Department of Physics, University of Zagreb, Croatia2 Department of Physics, Massachusetts Institute of Technology, USA

3 Faculty of Metallurgy, University of Zagreb, Croatia4 Faculty of Civil Engineering, University of Zagreb, Croatia

We study momentum distribution and free expansion of anyons, particles with fractional statistics intwo dimensions. We find that the 2D momentum distribution (MD), defined by the projection of thewavefunction onto kinetic momentum eigenstates (e.g., as it is defined for Bose or Fermi gases), isnot a proper observable for anyons, because perpendicular components of the kinetic momentum donot commute (this can be viewed as a signature of the vector charge-flux interactions). However, anappropriate observable which corresponds to the MD for anyons, which reduces to the usual definitionswhen the statistical parameter approaches 0 for bosons or 1 for fermions, is proposed from inspectionof free expansion. Namely, MD for anyons can be defined through the projection of the wave functiononto eigenstates for N anyons in free space, which are complex many-body eigenstates (not planewaves). With this definition, the asymptotic limit of the single-particle density of an anyonic gas "freely"expanding from a trap, corresponds to the initial momentum distribution of an anyonic gas. The quoteson "freely" emphasize that anyons are interacting via vector interactions (whose form depends on thechosen gauge). Our results are obtained by inspecting an exact time-dependent many-body wave-function, after the harmonic trap with N anyons is suddenly turned off, yielding a self-similar evolutionof the single-particle density. For the case of two anyons, we can study the observables analytically bycalculating projection coefficients of the time-dependent anyonic wave-function onto the free spaceanyonic eigenstates, which underpins our conclusions.

182



Semi-synthetic zigzag lattices

Egidijus Anisimovas,1 Mantas Raciunas,1 Christoph Sträter,2 André Eckardt,2 Ian Spielman,3 andGediminas Juzeliunas1

1 Vilnius University, Lithuania2 MPI PKS, Dresden

3 Joint Quantum Institute, NIST/UMD, USA

We consider a semi-synthetic “zigzag” lattice characterized by a triangular geometry [1]. The lattice canbe created combining a spin-dependent one-dimensional optical lattice with laser-induced transitionsbetween the atomic internal states. It is affected by a tunable homogeneous magnetic flux and featuresnonlocal interactions both in the synthetic and the real dimensions, because atoms in different internalstates are trapped at different spatial locations. Nonlocal interactions represent an important goal inrecent experiments, and previously such interactions have been engineered via superexchange dipole-dipole coupling or Rydberg dressing. We investigate the ground-state properties of the proposed systemfor the case of bosonic atoms with strong interactions using the density-matrix renormalization groupcalculations. In particular, we find that the interplay between the frustration induced by the magneticfield and the interactions gives rise to an exotic gapped phase at fractional per-site filling factorscorresponding to one particle per magnetic unit cell.

[1] E. Anisimovas, M. Raciunas, C. Sträter, A. Eckardt, I. B. Spielman, and G. Juzeliunas, Semi-synthetic zigzag optical lattice for

ultracold bosons, Phys. Rev. A 94, 063632 (2016).

183



Topological Floquet-Thouless energy pump

Michael Kolodrubetz,1,2 Frederik Nathan,3 Snir Gazit,2 Takahiro Morimoto,2 Mark Rudner,3 and JoelMoore1,2

1 Materials Sciences Division, Lawrence Berkeley National Laboratory2 Department of Physics, University of California, Berkeley

3 Niels Bohr Institute, University of Copenhagen

We study how the Thouless charge pump generalizes to the case of a periodically-driven Floquet system.We find that instead of pumping charge, it pumps energy in quanta of the driven frequency. Thisphenomenon is topologically protected by a winding number similar to that of the anomalous Floquetinsulator. We show how this topological pump may be used to adiabatically transport quanta of energyfrom one side of the system to the other. Quantizing the driven photons, we show how this may alsobe operated as a closed loop cavity QED pump, where the cavity photons are coherently absorbed oremitted by the system. We comment on the possibility of this physics in realistic experimental settings.

184



Quantum charge pumps with topological phases in Creutz ladder

Ning Sun and Lih-King Lim

Institute for Advanced Study, Tsinghua University, Beijing, China

Quantum charge pumping phenomenon connects band topology through the dynamics of a one-dimensional quantum system. In terms of a microscopic model, the Su-Schrieffer-Heeger/Rice-Melequantum pump continues to serve as a fruitful starting point for many considerations of topologicalphysics. Here we present a generalized Creutz scheme as a distinct two-band quantum pump model.By noting that it undergoes two kinds of topological band transitions accompanying with a Zak-phase-difference of π and 2π, respectively, various charge pumping schemes are studied by applying anelaborate Peierls phase substitution. Translating into real space, the transportation of quantized chargesis a result of cooperative quantum interference effect. In particular, an all-flux quantum pump emergeswhich operates with time-varying fluxes only and transports two charge units. This puts cold atomswith artificial gauge fields as an unique system where this kind of phenomena can be realized.

[1] arxiv:1703.03104 (2017).

185



Traveling Majorana solitons in a low-dimensional spin-orbit-coupled Fermisuperfluid

Peng Zou,1 Joachim Brand,2 Xia-Ji Liu,1 and Hui Hu1

1 Swinburne University of Technology, Melbourne2 Massey University, Auckland

We investigate traveling solitons of a one- or two-dimensional spin-orbit-coupled Fermi superfluid inboth topologically trivial and nontrivial regimes by solving the static and time-dependent Bogoliubov–deGennes equations. We find a critical velocity v for traveling solitons that is much smaller than thevalue predicted using the Landau criterion due to spin-orbit coupling. Above v, our time-dependentsimulations in harmonic traps indicate that traveling solitons decay by radiating sound waves. In thetopological phase, we predict the existence of peculiar Majorana solitons, which host two Majoranafermions and feature a phase jump of π across the soliton, irrespective of the velocity of travel. Theseunusual properties of Majorana solitons may open an alternative way to manipulate Majorana fermionsfor fault-tolerant topological quantum computations.

[1] P. Zou, J. Brand, X.-J. Liu, and H. Hu, Physical Review Letters 117, 225302 (2016).

186



Two-dimensional homogeneous Fermi gases

Klaus Hueck, Niclas Luick, Lennart Sobirey, Jonas Siegl, Thomas Lompe, and Henning Moritz

Institute for Laserphysics, University of Hamburg

We report on the experimental realization of homogeneous two-dimensional Fermi gases trapped in abox potential [1], which are ideally suited to probe local as well as non-local properties. Local probingis performed by imaging arbitrary intensity distributions onto the atoms, which enables us to extract theequation of state of a non-interacting 2D Fermi gas. We perform matter wave focusing to extract itsmomentum distribution and directly observe Pauli blocking in a near unity occupation of momentumstates. In the strongly interacting regime the momentum distribution of homogeneous 2D Fermi gases inthe crossover between weakly-bound fermionic pairs and deeply-bound bosonic molecules is measured.

[1] K. Hueck, N. Luick, L. Sobirey, J. Siegl, T. Lompe, and H. Moritz, arXiv:1704.06626 (2017).

187



Tying quantum knots

David S. Hall,1 Michael W. Ray,1 Konstantin Tiurev,2 Emmi Ruokokoski,2 Andrei H. Gheorghe,1 andMikko Möttönen2

1 Department of Physics and Astronomy, Amherst College2 QCD Labs, COMP Centre of Excellence, Department of Applied Physics, Aalto University

As topologically stable objects in field theories, knots have been put forward to explain various persistentphenomena in systems ranging from atoms and molecules to cosmic textures in the universe [1]. Recentexperiments have reported the observation of knots in different classical contexts [2] and monopolesin superfluids [3, 4]. However, no experimental observation of knots has previously been reported inquantum matter. Here we demonstrate the experimental creation and detection of knot solitons in theorder parameter of a spinor Bose–Einstein condensate [5]. The realized texture corresponds to the firsttopologically nontrivial element of the third homotopy group observed in the quantum regime. It alsoexhibits the celebrated Hopf fibration, which unites many seemingly unrelated physical phenomena [6].Thus these results critically expand the family of different types of topologies observed in nature andpave the way for studies of knot dynamics.

[1] W. Thomson, On vortex atoms, Proc. R. Soc. Edinburgh VI, 197 (1867).

[2] U. Tkalec, M. Ravnik, S. Copar, S. Zumer, and I. Musevic, Reconfigurable knots and links in chiral nematic colloids, Science 333,

62 (2011).

[3] M. W. Ray, E. Ruokokoski, K. Tiurev, M. Möttönen, and D. S. Hall, Observation of isolated monopoles in a quantum field, Science

348, 544 (2015).

[4] M. W. Ray, E. Ruokokoski, S. Kandel, M. Möttönen, and D. S. Hall, Observation of Dirac monopoles in a synthetic magnetic field,

Nature 505, 657 (2014).

[5] D. S. Hall, M. W. Ray, K. Tiurev, E. Ruokokoski, A. H. Gheorghe, and M. Möttönen, Tying quantum knots, Nat. Phys. 12, 478

(2016).

188



A simple tensor network algorithm for 2D steady states

Augustine Kshetrimayum,1 Hendrik Weimer,2 and Roman Orus1

1 University of Mainz2 University of Hannover

Here we present a tensor network algorithm that approximates steady-states of 2d quantum latticedissipative systems in the thermodynamic limit. The implementation of our method is remarkably simpleand efficient. We prove the validity of the approach by computing the steady states of a dissipativequantum Ising model, relevant to address controversies in dissipative systems of interacting Rydbergatoms, and benchmark our simulations with a variational algorithm based on product and correlatedstates. Our results support the existence of a first order transition in this model, while we find noevidence for a bistable region. Our method is the first implementation of the calculation of steady statesin 2d for quantum lattice systems with tensor networks.

[1] arXiv:1612.00656 (2016).

189



Dynamical quenched equilibration across the BEC phase transition in a trappedquantum gas

I-Kang Liu,1,2 Simone Donadello,3 Giacomo Lamporesi,3 Gabriele Ferrari,3 Shih-Chuan Gou,2 FrancoDalfovo,3 and Nick Proukakis1

1 Joint Quantum Centre (JQC) Durham-Newcastle, School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne,NE1 7RU, UK

2 Department of Physics, National Changhua University of Education, Changhua 50058, Taiwan3 INO-CNR BEC Center and Dipartimento di Fisica, Universita di Trento, 38123 Povo, Italy

We characterize the quench-induced emergence of a finite-size inhomogeneous ordered equilibriumquantum state from an uncorrelated thermal state through the dynamical crossing of the Bose-Einsteincondensation phase transition. Our work offers a unified analysis of spontaneous symmetry breaking,defect generation, interaction and decay, alongside the associated process of coherence growth in a finiteinhomogeneous system. Specifically, we use fully-3D stochastic simulations in the elongated geometry ofa recent experiment at Trento [1], finding excellent agreement with observations. Our unique numericalvisualization of density profiles, vortex number and linelength, and coherence during all stages of thenon-equilibrium dynamics enables us to address both the dependence of defect generation on quenchrate (Kibble-Zurek scaling law) and the extent to which this can be decoupled from the coarse-grainingequilibration dynamics in which defect propagation, interactions and decay dominate, thus sheddingmore light into the process by which coherence grows and the system rethermalizes.

[1] Donadello et al., Phys. Rev. A 94, 023628 (2016).

190



Observation of self-similar dynamics in a one-dimensional spinor Bose-Einsteincondensate

Maximilian Prüfer, Philipp Kunkel, Christian-Marcel Schmied, Anika Frölian, Daniel Linnemann,Helmut Strobel, Thomas Gasenzer, and Markus K. Oberthaler

Kirchhoff-Institute for Physics, University Heidelberg

After a quench of a many-particle system, two basic scenarios in the long-time dynamics are envisioned:One is the emergence of a quasi-stationary state most generally described by a generalized Gibbsensemble, the other scenario is self-similar dynamics. The latter is characterized by temporal rescalingof spatial correlation functions. Such behaviour is suggested by the concept of non-thermal fixed points.Employing a Bose-Einstein condensate of 87Rb in the F = 1 hyperfine manifold with ferromagneticinteractions, we can access experimentally the corresponding scaling exponents. We prepare our systemin the polar phase and quench it into the symmetry-broken ferromagnetic phase. After a build-up ofexcitations in the transversal spin we observe a self-similar evolution, which is due to redistributionof excitations among different momenta. By rescaling the power spectra of the transversal spin, wedetermine the scaling exponents as well as universal scaling functions.

191



Superfluid in a shaken optical lattice: Quantum critical dynamics andtopological defect engineering

Anita Gaj, Lei Feng, Logan W. Clark, and Cheng Chin


We present our recent studies of non-equilibrium dynamics in Bose-Einstein condensates using theshaken optical lattice. By increasing the shaking amplitude we observe a quantum phase transitionfrom an ordinary superfluid to a ferromagnetic superfluid composed of discrete domains with differentquasi-momentum. We investigate the critical dynamics during which the domain structure and domainwalls emerge. We demonstrate the use of a digital micromirror device to deterministically create desireddomain structure. Using this technique we develop a clearer picture of the quantum critical dynamics inearly times and its impact to the domain structure long after the transition.

192



Cavity-enhanced transport of charge

Guido Pupillo

University of Strasbourg

We theoretically investigate charge transport through electronic bands of a mesoscopic one-dimensionalsystem, where inter-band transitions are coupled to a confined cavity mode, initially prepared in itsvacuum. This coupling leads to light-matter hybridization where the dressed fermionic bands interactvia absorption and emission of dressed cavity-photons. Using a self-consistent non-equilibrium Green’sfunction method, we compute electronic transmissions and cavity photon spectra and demonstrate howlight-matter coupling can lead to an enhancement of charge conductivity in the steady-state. Dependingon the ratio between cavity loss rate and electronic bandwidth, the system dynamics involves either acollective or an individual response of Bloch states, and explain how this affects the current enhancement.We show that under certain experimentally relevant conditions the charge conductivity enhancementcan reach orders of magnitudes.

[1] David Hagenmüller, Johannes Schachenmayer, Stefan Schütz, Claudiu Genes, and Guido Pupillo, Cavity-enhanced transport of

charge, arXiv:1703.00803 (2017).

193



Phase-space curvature in spin-orbit-coupled ultracold atomic systems

Julius Ruseckas, Jogundas Armaitis, and Egidijus Anisimovas

Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio ave. 3, LT-10222 Vilnius, Lithuania

The Berry phase, as well as Berry curvatures in real and momentum spaces, has been thoroughlydiscussed in the literature in various contexts [1]. However, up to now considerably less attention hasbeen paid to phase-space Berry curvatures. Here we approach the phase-space Berry curvature withapplications in ultracold-atom systems in mind. We consider ultracold atom systems with artificiallyengineered spin-orbit coupling [2], which have recently attracted considerable attention. Some of theproposed spin-orbit-coupling schemes have already been experimentally realized. We derive quantum-mechanical Heisenberg equations of motion where position-space, momentum-space, and phase-spaceBerry curvatures show up without relying on the semiclassical approximation [3]. Subsequently, weperform the semiclassical approximation and obtain the semiclassical equations of motion. Taking thelow-Berry-curvature limit results in equations that can be directly compared to previous results forthe motion of wave packets. We show that in the semiclassical regime the effective mass of the equalRashba-Dresselhaus spin-orbit-coupled system can be viewed as a direct effect of the phase-space Berrycurvature.

[1] N. Goldman, G. Juzeliunas, P. Ohberg, and I. B. Spielman, Rep. Prog. Phys. 77, 126401 (2014).

[2] J. Dalibard, F. Gerbier, G. Juzeliunas, and P. Ohberg, Rev. Mod. Phys. 83, 1523 (2011).

[3] J. Armaitis, J. Ruseckas, and E. Anisimovas, Phys. Rev. A 95, 043616 (2017).

194



Dephasing and relaxation of bosons in 1D: Newton’s cradle revisited

Chen Li,1 Tianwei Zhou,1 Tian Luan,1 Qi Hua,1 Zijie Zhu,1 Wei Xiong,1 Xiaoji Zhou,1 Xuzong Chen,1

and Jörg Schmiedmayer2

1 School of Electronics Engineering and Computer Science, Peking University, Beijing, China2 Vienna Center for Quantum Science and Technology (VCQ), Atominstitut, TU-Wien, Vienna, Austria

We study the relaxation of ultracold bosons (87Rb) in one dimension in a setting similar to the originalNewton’s cradle experiment [1]. We start with a BEC in a 2D optical lattice (a lattice of 1D tubes) withvery little heating (< 0.01ħhω/sec) and negligible loss (< 7% in 5 seconds). We excite the atoms tooscillate and collide in the 1D tubes by coherent pulses and observe the oscillations for up to about 5seconds (400 oscillations). Tuning the energy put into the longitudinal motion we can probe the onsetof thermalization due to breaking of integrability in the cross over between 1D and 3D. We observede-phasing of the oscillations and then thermalisation (= gaussification of the momentum distribution)even for samples where the energy put into the system is not sufficient to excite transverse motion(initial collision energy < 0.5 energy needed for transverse excitations), and the smallest number ofatoms per tube (γ∼ 5). The final state follows very closely the statistical (non-degenerate) descriptionof a thermalized classical 1D gas of bosons. Investigating the population of the transverse excited statesby band mapping, we verify that the relaxation/thermalizaton proceeds through atoms in transverseexcited states. We conjecture that the relaxation is triggered by the very small excitations produced bythe residual heating (< 0.01ħhω/sec). Observing the effective 3 body processes [2] that are predicted tobreak the integrability even in a fully 1-dimensional setting will need even much smaller heating rates,or efficient removal of atoms in transvers excited states.

X. Z. Chen acknowledges support by the NSFC (No. 91336103, No. 10934010 and No. 61078026).J. S. acknowledges support by the EU through the ERC-AdG QuantumRelax.

[1] T. Kinoshita et al., Nature 440, 900 (2006); for a recent study using polar molecules, see: Yijun Tang et al. arXiv:1707.07031

(2017).

[2] I. Mazerts et al., Phys. Rev. Lett. 100, 210403 (2008); S. Tan et al., Phys. Rev. Lett. 100, 090404 (2010).

195



Vortex mass in a superfluid

Tapio Simula

School of Physics & Astronomy, Monash University, Victoria 3800, Australia

We consider the inertial mass of a vortex in a superfluid quantum gas. In contrast to the conclusion byThouless and Anglin [1], we obtain a vortex mass that is well defined and is determined microscopicallyand self-consistently by the elementary excitation energy of the kelvon quasiparticle localised within thevortex core [2]. In agreement with the observations by the Zwierlein group [3,4], the vortex is foundto be heavy due to the low excitation energy of the kelvon. The mass, Magnus force, and Berry phaseof the vortex could be measured experimentally in superfluid Bose and Fermi gases using currentlyavailable methodologies.

[1] D. J. Thouless and J. R. Anglin, Vortex mass in a superfluid at low frequencies, Phys. Rev. Lett. 99, 105301 (2007).

[2] T. Simula, Vortex mass in a supefluid, arXiv:1704.08410 (2017).

[3] Tarik Yefsah, Ariel T. Sommer, Mark J. H. Ku, Lawrence W. Cheuk, Wenjie Ji, Waseem S. Bakr, and Martin W. Zwierlein, Heavy

solitons in a fermionic superfluid, Nature 499, 426 (2013).

[4] M. J. H. Ku, W. Ji, B. Mukherjee, E. Guardado-Sanchez, L. W. Cheuk, T. Yefsah, and M. W. Zwierlein, Motion of a solitonic vortex

in the BEC-BCS crossover, Phys. Rev. Lett. 113, 065301 (2014).

196



Quantum dynamics of a Bose gas quenched to unitarity

Robert Smith, Christoph Eigen, Jake Glidden, and Zoran Hadzibabic


We study the dynamics of a homogeneous Bose gas following a sudden quench of the scattering lengthto, and then away from, unitarity. We measure the atom number and energy of the cloud as a functionof time at unitarity. For low phase-space density we observe a clear separation of two- and three-bodyphysics, initially we observe a rapid increase in kinetic energy without any accompanying loses followedby atom-loss and heating on a slower timescale due to three-body losses. As the phase-space density isincreased the qualitative behaviour remains the same but the two timescales begin to converge; for a(quasi) pure Bose-Einstein condensate (BEC) at unitarity the interparticle spacing is the only relevantlengthscale and so both timescales should be multiples of the associated ‘Fermi time’ tF ∼

mħh n−2/3 where

n is the density and m the atomic mass. We see excellent agreement with this n−2/3 scaling for morethan an order of magnitude in density as long as energy of the cloud remains below the related ‘Fermienergy’.

197



Generation of atypical hopping and interactions by kinetic driving

Gregor Pieplow, Fernando Sols, and Charles E. Creffield

Universidad Complutense de Madrid

We study the effect of time-periodically varying the hopping amplitude in a one-dimensional Bose-Hubbard model, such that its time-averaged value is zero. Employing Floquet theory, we derive a staticeffective Hamiltonian in which nearest-neighbor single-particle hopping processes are suppressed, butall even higher-order processes are allowed. Unusual many-body features arise from the combined effectof nonlocal interactions and correlated tunneling. At a critical value of the driving, the system passesfrom a Mott insulator to a superfluid formed by two condensates with opposite nonzero momenta. Thepresent work shows how driving of the hopping energy provides a novel form of Floquet engineering,which enables atypical Hamiltonians and exotic states of matter to be produced and controlled.

198



Quantum gases in cavities and lattices

Dan Stamper-Kurn1,2

1 University of California, Berkeley2 Lawrence Berkeley National Laboratory

I will review recent results from studying quantum gases trapped within optical resonators, includingresults on cavity optomechanics, cavity spin optodynamics, and light-induced spin-orbit coupling andthe negative mass instability. I will also discuss studies of quantum gases in an optical superlattice,including a precise test of the scaling hypothesis for the Bose-Hubbard Hamiltonian and efforts to createnew geometries of two-dimensional lattices.

199



Spin superfluidity of a Bose gas mixture at finite temperature

Eleonora Fava, Tom Bienaimé, Carmelo Mordini, Giacomo Colzi, Chunlei Qu, Sandro Stringari,Giacomo Lamporesi, and Gabriele Ferrari

INO-CNR BEC Center and Dipartimento di Fisica, University of Trento; Trento Institute for Fundamental Physics and Applications,

INFN, 38123 Povo, Italy

The spin-dipole oscillation of a harmonically trapped Bose-Einstein condensed binary mixture of sodiumatoms is investigated at finite temperature. We report experimental evidence for the persistence ofoscillating spin supercurrents, even in the presence of a large thermal component. While the condensatealways exhibits the spin oscillation, the thermal component behaves differently, depending on whetherthe system is in the collisionless or collisional regime. For dilute samples the thermal component isdriven by the mean field interaction with the condensate and oscillates with same frequency but oppositephase. For denser samples, in the collisional regime, the thermal component of the spin current isinstead damped due to spin drag. We also measure the static polarizability of the condensed and thermalparts and we find a large increase of the condensate polarizability with respect to the T = 0 value, inagreement with the predictions of theory theory.

200



Strongly interacting homogeneous Fermi gases

Julian Struck,1,2 Biswaroop Mukherjee,1 Zhenjie Yan,1 Parth B. Patel,1 Airlia Shaffer-Moag,1 CedricWilson,1 Richard Fletcher,1 and Martin W. Zwierlein1

1 MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute ofTechnology, Cambridge, Massachusetts 02139, USA

2 Laboratoire Kastler Brossel, CNRS, ENS-PSL Research University, UPMC-Sorbonne Universités and Collège de France, Paris 75005,

France

Recently, we have created homogeneous atomic Fermi gases in a uniform potential [1]. In the momentumdistribution of a spin-polarized gas, we observed the emergence of the Fermi surface and the saturatedoccupation of one particle per momentum state: a direct consequence of Pauli blocking for a degenerategas. In general, a spatially constant chemical potential is an essential prerequisite for studies of criticalphenomena, where the correlation length diverges, and for measurements of trap-averaged observables,such as the momentum distribution of the gas. Here, we report on measurements of strongly interactinghomogenous Fermi gases. This includes the measurement of the contact of a unitary Fermi gas acrossthe normal- to superfluid transition and the study of collective excitations of the gas in the BEC to BCScrossover. Furthermore, we will present thermodynamic measurements of spin imbalanced Fermi gases.

[1] B. Mukherjee, Z. Yan, P. B. Patel, Z. Hadzibabic, T. Yefsah, J. Struck, and M. W. Zwierlein; Phys. Rev. Lett. 118, 123401 (2017).

201



Granulation in Bose-Einstein condensates as manifestation of quantumfluctuations

Marios C. Tsatsos

Sao Carlos Institute of Physics - USP

Quantum fluctuations are inherent to any microscopic system and manifest the very probabilistic natureof quantum matter. In Bose-Einstein condensates (BECs) however, where typically 104 or more atomsare trapped, fluctuations are washed out due to the large particle number together with long-rangecoherence and, hence, absence of quantum correlations. Hence conventional mean-field theories areconsidered apt for the full description of BEC dynamics. Nevertheless, in a recent joint work betweenUSP and Rice university granulated states in elongated condensates of lithium-7 atoms have beenobserved. Our analysis shows that the latter cannot be explained via mean-field alone; one arrives atthe conclusion that the emergence and proliferation of grains is described via a many-body approach,that takes correlations and fragmentation into account. Here the main characteristics of the observedgranulated states are presented as well as results that go beyond the Gross-Pitaevskii theory, obtainedby solving the MCTDHB equations. While the (undulated) density alone shows no granulation, anaccurate simulation of single shots indeed shows grains, i.e. spatially separated regions of atoms.Therefore, granulation consists a case study where higher-order correlations of zero-temperature gasesare paramount and the accurate description of the experiment cannot rely on GP or other mean-fieldtheories.

202



Engineering an optical solenoid for quantum gases

F. Nur Unal, Botao Wang, and Andre Eckardt

Max-Planck-Institute for the Physics of Complex Systems

The idea of inserting a local magnetic flux, representing the field of a thin solenoid, plays an importantrole in various condensed matter models, especially in the understanding of topological systems. Oneexample is the creation and manipulation of quasiparticle or quasihole excitations in these systems,which are essential for fault-tolerant quantum information processing. Implementing such local fluxesin cold atom experiments promises great potential. Here, we propose an experimental scheme torealize a local flux in a cold atom setting which takes advantage of the recent developments in syntheticgauge fields and quantum microscopes. To demonstrate the feasibility of our method, we considerquantum-Hall-type lattice systems and study the dynamical creation of topological excitations. Weanalyze the adiabatic charge pumping by tuning the strength of the local flux.

203



Momentum distribution and symmetry characterization of one-dimensionalstrongly interacting Fermi gases

Patrizia Vignolo,1 Jean Decamp,1 Johannes Jünemann,2 Matteo Rizzi,2 Mathias Albert,1 and Anna

Minguzzi3

1 Institut de Physique de Nice, 1361 route des Lucioles, 06560 Valbonne,France2 Johannes Gutenberg-Universität, Institut für Physik, Staudingerweg 7, 55099 Mainz, Germany

3 Laboratoire de Physique et Modélisation des Milieux Condensés, avenue des Martyres, 38042 Grenoble, France

One dimensional (1D) strongly correlated quantum systems are nowadays the subject of intense the-oretical and experimental activity. In such systems, the momentum distribution is a powerful probeof both gas statistics and of the intertwined effect of interactions between particles and the effectivedimensionality they move in. A remarkable momentum distribution feature, in all dimensions, is thepresence of universal power-law tails n(k) k−4 for a gas where interactions can be schematized as contactones. The weight of such tails, denoted as Tan’s contact, can be put into relation with several many-bodyquantities, ranging from the interaction energy to the depletion rate by inelastic collisions. In this work,we show that such tails also encode precious information about the permutational symmetry of 1Dstrongly correlated mixtures.More in details, we calculate, at finite and infinite interactions, the momentum distribution tails for amixture of κ fermionic components under 1D harmonic confinement and interacting among each otherwith completely SU(κ)-symmetric repulsive contact interactions. We show that both the ground andexcited states of the system have a well defined symmetry [1], thus indicating magnetic-like propertiesof the mixture, and that such information is fully encoded in the Tan’s contact [2].

[1] Jean Decamp, Pacome Armagnat, Bess Fang, Mathias Albert, Anna Minguzzi, and Patrizia Vignolo, Exact density profiles and

symmetry classification for strongly interacting multi-component Fermi gases in tight waveguides, New Journal of Physics 18, 055011

(2016).

[2] Jean Decamp, Johannes Jünemann, Mathias Albert, Matteo Rizzi, Anna Minguzzi, and Patrizia Vignolo, High-momentum tails

as magnetic structure probes for strongly-correlated SU(k) fermionic mixtures in one-dimensional traps, Phys. Rev. A 94, 053614

(2016).

204



Impurity and soliton dynamics in a Fermi gas with nearest-neighborinteractions

Anne-Maria Visuri,1,2 Päivi Törmä,2 and Thierry Giamarchi1

1 Department of Quantum Matter Physics, University of Geneva, 24 quai Ernest-Ansermet, 1211 Geneva, Switzerland2 COMP Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland

Using the numerical time-evolving block decimation method and simplified analytic models, we studyspinless fermions with repulsive nearest-neighbor interactions perturbed by an impurity particle or alocal potential quench. We investigate both a Mott insulator initial state where alternating lattice sitesare occupied and an incommensurate initial state which contains solitons of two neighboring occupiedsites.We show that the perturbations create a soliton-antisoliton pair, which leads to two types of processes[1]. In the first process, the soliton and antisoliton propagate in opposite directions while the impuritystays at the initial position. In the second one, the impurity is bound to the antisoliton while the solitonpropagates—a process where the impurity and bath are closely coupled. Furthermore, when solitons arealready present in the initial state, the soliton and antisoliton have a drastically different dynamics: Theantisoliton does not annihilate with the solitons and is therefore confined close to its origin while thesoliton excitation propagates [2]. We discuss the possibility of observing these excitations in experimentswith ultracold gases.

[1] A.-M. Visuri, T. Giamarchi, and P. Törmä, Excitations and impurity dynamics in a fermionic Mott insulator with nearest-neighbor

interactions, Phys. Rev. B 93, 125110 (2016).

[2] A.-M. Visuri, P. Törmä, and T. Giamarchi, Impurity and soliton dynamics in a Fermi gas with nearest-neighbor interactions,

arXiv:1701.01845 (2017).

205



Atomtronics with adiabatic potentials

Wolf von Klitzing, Saurabh Pandey, Hector Mas, Vasiliki Bolpasi, Costas Poulios, and Georgos Vasilakis

IESL-Forth

Atom interferometers are some of the most sensitive instruments available to date. One of their limitingfactors is the finite interaction time due to the atoms being accelerated in earth’s gravitational potential.Attempts to overcome this using external potentials have been largely flawed by the lack of smoothwave guides.Here, we report on the development of ultra-smooth coherent matterwave guides based on time averagedadiabatic potentials (TAAP) [1,2], where we now can transport BECs over macroscopic distanced andhave them interact with precisely engineered potentials. We will then present our progress towards anovel ‘clock-type’ Sagnac interferometer based on state-dependent manipulation of atoms in waveguidesusing time-averaged adiabatic potentials. We demonstrate, in analogy to the magic frequency of thestrontium lattice clocks, that by carefully tuning the confining potential a magic-field strength can befound such that the dependence on the guiding potential vanishes [3].

[1] P. Navez et al., N. J. Phys. 18, 075014 (2016).

[2] I. Lesanovsky and W. von Klitzing, PRL 99, 083001 (2007).

[3] P. Treutlein et al., PRL 92, 203005 (2004).

206



Necklace-like states in toroidally trapped Rashba spin-orbit coupledBose-Einstein condensates

Angela White,1 Yongping Zhang,1,2 and Thomas Busch1

1 Quantum Systems Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan2 Department of Physics, Shanghai University, Shanghai 200444, China

Superfluid properties of rotating two-component Bose–Einstein condensates change as a function of theinteraction energy through the phase transition from miscibility to immiscibility. Azimuthally phase-separated states in toroidally trapped condensates have been shown to exhibit classical solid-bodyrotation despite the quantum nature of superfluid flow [1]. Introducing Rashba spin-orbit coupling inthe absence of rotation leads to necklace states in the immiscible regime. These necklace states composedof azimuthally phase-separated density lobes, mimic the density profiles expected for many-componentcondensates in the immiscible regime, and are a unique manifestation of the well-know stripy phasearising in spin-orbit coupled condensates [2]. In the miscible regime, persistent current states are found,with a unit winding difference between each component. We show that both the winding numbers inthe persistent current states and the number of density lobes composing the necklace-like states arehighly-tuneable and depend on the spin-orbit coupling strength [2].

[1] A. White, T. Hennessy, and Th. Busch, Phys. Rev. A 93, 033601 (2016).

[2] A. White, Y. Zhang, and Th. Busch, Phys. Rev. A 95, 041604(R) (2017).

207



Towards ultracold dipolar molecules in two dimensions

Sebastian Will

Columbia University

Ultracold molecules open up new routes for precision measurements, quantum information processingand many-body quantum physics. In particular, dipolar molecules with long-range interactions promisethe creation of novel states of matter, such as topological superfluids and quantum crystals. Dipolarmolecules can be efficiently assembled from ultracold atoms. Using this approach we have createdthe first ultracold gases of strongly dipolar NaK molecules in previous work with our collaborators atMIT [1]. We have demonstrated coherent microwave control over rotational and hyperfine states ofNaK [2] and observed a coherence time on the order of one second for superpositions of the lowestmolecular hyperfine states [3]. These results open exciting prospects for precision metrology andquantum information.Building on the remarkable quantum control that has been achieved on the single molecule level, weare setting out to study the many-body physics of strongly dipolar ground state molecules in our newlabs at Columbia University. We plan to create and confine a quantum degenerate molecular gas to asingle two-dimensional plane and study its phases and phase transitions—from a strongly correlatedsuperfluid to a two-dimensional dipolar crystal.

[1] PRL 114, 205302 (2015).

[2] PRL 116, 225306 (2016).

[3] arXiv:1606.04184 (2016).

208



Emergence of non-abelian magnetic monopoles in a quantum impurity problem

E. Yakaboylu, A. Deuchert, and M. Lemeshko

IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400 Klosterneuburg, Austria

Recently it was shown that molecules rotating in superfluid helium can be described in terms of theangulon quasiparticles [1]. Here we demonstrate that in the experimentally realized regime the anguloncan be seen as a point charge on a 2-sphere interacting with a gauge field of a non-abelian magneticmonopole [2]. Unlike in several other settings, the gauge fields of the angulon problem emerge in the realcoordinate space, as opposed to the momentum space or some effective parameter space. Furthermore,we find a topological transition associated with making the monopole abelian, which takes place in thevicinity of the previously reported angulon instabilities. The angulon instabilities correspond to orbitalangular momentum transfer between the impurity and the bath, at which very strong, ‘anomalous’screening can take place in the presence of a neutral, weakly-polarizable environment [3]. These resultspave the way for studying topological phenomena in experiments on molecules trapped in superfluidhelium nanodroplets, as well as on other realizations of orbital impurity problems.

[1] M. Lemeshko, Phys. Rev. Lett. 118, 95301 (2017).

[2] E. Yakaboylu, A. Deuchert, and M. Lemeshko,arXiv:1705.05162 (2017).

[3] E. Yakaboylu and M. Lemeshko, Phys. Rev. Lett. 118, 85302 (2017).

209



Spatial entanglement and Einstein-Podolsky-Rosen steering in a Bose-Einsteincondensate

Tilman Zibold, Matteo Fadel, Boris Decamps, and Philipp Treutlein

Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland

We investigate the spatial entanglement in a spin squeezed Bose-Einstein condensate of rubidium atoms.By letting the atomic cloud expand and using high resolution absorption imaging we are able to accessthe spatial spin distribution of the many-body state. The observed spin correlations between differentregions go beyond classical correlations and reveal spatial non-separability. Furthermore they allow forEPR steering of a subregion of the atomic spin. By inferring measurement outcomes of non-commutingobservables in one region based on measurements in a separate region we are able to seemingly beatthe Heisenberg uncertainty relation, realizing the EPR paradox with an atomic system. Our findingscould be relevant for future quantum enhanced measurements of spatially varying observables such aselectromagnetic fields.

210

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