EU Research and Training Network

Cold Molecules: Formation,

Trapping, and Dynamics

Coordinator: Françoise Masnou-Seeuws, Orsay

Contract HPRN – CT – 2002 – 00290

21 – 23 February 2005, »Gartensaal« in the »Neue Rathaus«,

Hannover, Germany

8.00 8.00

8.30 8.30

Welcome 9.00 9.00

9.30 9.30

Stwalley Pinkse

Rep

ort

s b

y th

e te

ams Austrap

Hann./Freiburg

Roma

Utrecht

10.00 10.00

Report II

Drewsen Bethlem

10.30 10.30

Young Researchers

Coffee Coffee 11.00 11.00

Coffee

11.30 11.30

Léonard Launay

Discussion

12.00 12.00

Comm. Rep./Exp. Adv.

Arndt

Gianturco

12.30 12.30

13.00 13.00

Lunch Lunch Lunch

13.30 13.30

Comm. Rep./Exp. Adv. 14.00 14.00

Report I 14.30 14.30

15.00 15.00

15.30 15.30

Intr

od

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n

Te

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FHI-Berlin

Imperial

Jerusalem

Orsay Theo. Co

ntr

ibu

ted

ta

lks

Carty Lisdat

Schmelcher Schiller Pichler Vogels Dulieu Auböck

Co

ntr

ibu

ted

ta

lks

Nagl

Ernst

Weidemüller

Bakker

Jun Ye 16.00 16.00

Coffee Coffee

16.30 16.30

Hot Topics

Kosloff Pillet

17.00 17.00

17.30 17.30

Network coordination,

planning 2005/06

18.00

Düsseldorf Pisa

Orsay Exp. Storrs Zagreb 18.00

Re

po

rt b

y

th

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ea

ms

Coffee and

Poster session

18.30 18.30 19.00 19.00

19.30 19.30 20.00 20.00

Grimm

Workshop Dinner

20.30 20.30

Midterm Review of the EU Research and Training Network and

Workshop

Applications and dynamics of cold molecules Organisers:

Eberhard Tiemann, Hannover Olivier Dulieu, Orsay

Secretary: Elke Hünitzsch, Hannover Katrin Pfennig, Hannover

Book of Abstracts: Christian Lisdat, Hannover

21 – 23 February 2005 »Gartensaal« in the »Neue Rathaus«

Hannover, Germany

Technical Information

If any questions arise during the workshop, please feel free to contact Ms Hünitzsch in

the workshop secretary or any local participant. For some of the more obvious

questions, we have prepared some remarks below.

Oral presentations:

Computer presentation

We provide a notebook to put a PowerPoint or Acrobat Reader presentation via a

memory stick on. PowerPoint for Office XP will be installed. To our knowledge this

version is downward compatible. To be sure about the format etc. please use the

pack&go feature (supplied by your PowerPoint installation at home) or use the

embedded format feature for character fonts in your PowerPoint file.

During the session we have three additional connections for individual notebooks,

which provide a regular VGA connector.

Overhead projection

Yes, we will provide additionally an over head projector.

If you need other support, please tell us immediately. We will try to help.

Poster presentations:

For the poster session we have boards which will accommodate the format 92 cm width

and 121 cm height (called A0 portrait). The poster can be put up at Monday noon and

can be kept during the whole workshop until Wednesday noon.

Restaurants for dinner:

Dinner will not be provided by the workshop with the exception of the workshop dinner

on Tuesday. On the following page we have prepared a map with restaurants within a

few minutes walking distance.

1

Restaurants and Strassenbahn stations

Kabuki SoulFriedrichswall 10

Spaghetti PalastKarmaschstr. 16

MaredoGeorgstr. 38

BavariumWindmühlenstr. 3

Ständige VertretungFriedrichswall 10

Gartensaal

U-BahnAegi

U-BahnMarkthalle

Walking distance between 5 and 10 minutes.

2

Sunday 20 February 2005

Up to 18.00 Arrival

Pro

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e

Monday 21 February 2005

08.30 – 09.00 Welcome to the workshop Young researchers introduce themselves

Morning Session – 9 Chair: Peter van der Straten

09.00 – 09.45 William C. Stwalley »Photoassociation spectra, photoassociative molecule formation and

trapping of ultracold 39K85Rb«

09.45 – 10.30 Michael Drewsen »Cold molecular ion studies in traps«

10.30 – 11.00 Coffee

11.00 – 11.45 Jérémie Léonard »Photoassociation in an ultracold gas of metastabile helium«

11.45 – 12.30 Markus Arndt »Exploration of new methods for quantum optics with macromolecules«

12.30 – 13.30 Lunch

Afternoon Session Chair: Françoise Masnou

13.30 – 13.45 Introduction, commission representative, expert advisors

13.45 – 14.15 Report I by the co-ordinator Françoise Masnou

14.15 – 16.00 Introduction of the teams by the scientist-in-charge, Report by young researcher – 15

FHI Berlin 14.15 Meijer / Vanhaecke Imperial 14.40 Sauer / Mueller Jerusalem 15.05 Kosloff / Jørgensen Orsay Theo. 15.30 Masnou / Koch

16.00 – 16.30 Coffee

16.30 – 18.15 Introductions and Reports continued Düsseldorf / Humboldt 16.30 Schiller / Blythe Pisa 16.55 Gabanini / Lozeille Orsay Exp. 17.20 Pillet / Mudrich Storrs 17.45 Stwalley Zagreb 18.00 Pichler

18.15 – 19.30 Supper (individually)

Evening Talk – 23 Chair: Eberhard Tiemann

19.30 – 20.30 Rudi Grimm »BEC and more exciting physics with ultracold molecules«

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Tuesday 22 February 2005

Pro

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e Morning Session – 27 Chair: Gerard Meijer

08.15 – 09.55 Introduction of the teams by the scientist-in-charge, Report by young researcher

Austrap 08.15 Grimm / Kraemer Hannover / Freiburg 08.40 Tiemann / Staanum Roma 09.05 Gianturco / Bodo Utrecht 09.30 v. d. Straten / Nehari

09.55 – 10.05 Report II: Administrative and Financing Procedures for the Network by Olivier Dulieu

10.05 – 10.45 Open discussion: Meeting of young researchers and commission representative

10.45 – 11.15 Coffee

11.15 – 12.00 Open discussion between all members

12.00 – 12.10 First impressions and remarks by commission representative and expert advisor

13.00 – 14.00 Lunch

Afternoon Session Chair: Matthias Weidemüller

14.00 – 16.00 Contributed Talks – 33 14.00 David Carty 14.15 Christian Lisdat 14.30 Peter Schmelcher 14.45 Stephan Schiller 15.00 Goran Pichler 15.15 Johnny Vogels 15.30 Olivier Dulieu 15.45 Gerald Auböck

16.00 – 18.30 Coffee and Poster Session – 43

18.30 Workshop Dinner

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Wednesday 23 February 2005

Pro

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e Morning Session – 57 Chair: Ronnie Kosloff

09.00 – 09.45 Pepijn W. H. Pinkse »Trapping slow dipolar molecules in three and two dimensions

using static and switching electric fields«

09.45 – 10.30 Hendrick L. Bethlem »Deceleration and trapping of polar molecules

in high field seeking states«

10.30 – 11.00 Coffee

11.00 – 11.45 Jean-Michel Launay »Quantum dynamics of alkali atom – alkali dimer collisions

involving three identical spin-stretched atoms«

11.45 – 12.30 Franco Gianturco Introduction to »Ultracold chemistry, interaction forces and energy

transfer in reactive and quenching collision« followed by discussion and vision from all members

12.30 – 13.30 Lunch

Afternoon Session Chair: Olivier Dulieu

14.00 – 15.30 Contributed Talks – 63 14.00 Johann Nagl 14.15 Wolfgang Ernst 14.30 Matthias Weidemüller 14.45 Joost M. Bakker 15.00 Jun Ye

16.00 – 16.30 Coffee

16.30 – 17.00 Hot Topics – 69 16.00 Ronnie Kosloff 16.30 Pierre Pillet

17.00 – 18.00 Network Organisation, planning 2005 / 06

5

Thursday 24 February 2005

Pro

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e Lab Tours:

Institute for Quantum Optics

Departure from Hotel: 9.00 am by Strassenbahn stop »Aegi«, see map on page 2,

take line 4 (direction »Garbsen«) or line 5 (direction »Stöcken«),

leave at stop »Universität«.

Laser Zentrum Hannover

Departure from Hotel: 9.00 am by Strassenbahn stop »Aegi«, see map on page 2,

take line 4 (direction »Garbsen«), leave at stop »Marienwerder/Wissenschaftspark«,

go by foot to the LZH Hannover.

Arrival back at Hannover University around 12.30 h in the afternoon. Use line 4

(direction »Roderbruch«), leave at stop »Universität« and contact secretary’s office.

Possibility to have lunch in the students’ restaurant »Mensa«. Join the group from PTB

for a lab tour in the Institute of Quantum Optics.

Physikalisch-Technische Bundesanstalt (PTB)

Departure from Hotel: 8.00 am by bus.

Visit of labs: Time and Frequency, Quantum Optics with Cold Atoms, Josephson Effect.

Possibility for lunch at the PTB.

Arrival back at Hannover University around 14.00 h, contact secretary’s office.

Possibility for lab tour in the Institute of Quantum Optics.

6

Contributed Posters – 43

P 1 Olivier Allard, Stephan Falke: »Interactions between 1S and 3P calcium atoms:

study for cold molecule formation«

Lis

t o

f P

os

ters

P 2 Enrico Bodo: »Ultracold collision dynamics involving molecular systems«

P 3 Paul Condylis: »Measurement of the electron electric dipole moment using cold YbF molecules«

P 4 Anne Crubellier, Eliane Luc-Koenig: »Threshold effects in the photoassociation of cold atoms:

R–6 model in the Milne formalism«

P 5 Richard Darnley: »Decelerating heavy polar molecules«

P 6 Stephan Falke, Christian Lisdat: »Experimental investigation of ultra-cold collisions of potassium«

P 7 Reece Geursen: »Creation of a Bose-Einstein condensate of molecules and strongly interacting

Fermi gases in the BEC-BCS crossover«

P 8 Christiane Koch: »Formation of stable ultracold molecules after

photoassociation with chirped pulses«

P 9 Jérôme Lozeille: »Analysis of the multiphoton ionization of cold rubidium dimers«

P 10 Bernhard Roth, Stephan Schiller: »Sympathetic cooling of complex molecules progress report«

P 11 K. M. R. van der Stam: »Atom entanglement by Kapitza-Dirac superradiance«

P 12 Johnny Vogels: »Building on atom laser, the subsonic way«

P 13 Mireille Aymar, Olivier Dulieu: »Calculation of permanent and transition dipole moments of dipolar molecules«

P 14 Sebastian Jung, Christian Lisdat: »Towards Stark deceleration of SO2 to investigate its cold photofragmentation«

P 15 Driss Nehari: »Photoassciation of cold metastable helium atoms: from 1 to 2 color transition«

P 16 Michael Stoll, Joost Bakker: »Towards magnetic trapping of ultracold polar molecules«

P 17 Torben Mueller: »Production of cold molecular radicals by laser ablation and

supersonic expansion – A study«

P 18 Nicolas Vanhaecke: »Deceleration and electrostatic trapping of OH radicals«

P 19 Matthias Weidemüller: »Formation of cold bialkali molecules on helium nanodroplets«

7

Monday 21 February 2005

Morning session

(9.00 – 12.30)

Chair: Peter van der Straten

09.00 – 09.45 William C. Stwalley – 10

09.45 – 10.30 Michael Drewsen – 11

10.30 – 11.00 Coffee

11.00 – 11.45 Jérémie Léonard – 12

11.45 – 12.30 Markus Arndt – 13

9

The Photoassociative Spectroscopy, Photoassociative Molecule Formation,

and Trapping of Ultracold 39K 85Rb

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WILLIAM C. STWALLEY

University of Connecticut

We have observed the photoassociative spectra of colliding ultracold 39K and 85Rb atoms to produce K Rb* in all eight bound electronic states correlating with the 39K (4 s) + 85Rb (5 p1/2 and 5 p3/2) asymptotes. These electronically excited K Rb* ultracold molecules are detected after their radiative decay to the metastable triplet (a 3Σ+ ) state and (in some cases) the singlet (X 1Σ+ ) ground state. The triplet (a 3Σ+ ) ultracold molecules are detected by two-photon ionization at 602.5 nm to form K Rb+, followed by time-of-flight mass spectroscopy.

We are able to assign a majority of the spectrum to three states (2 (0+ ), 2 (0– ), 2 (1)) in a lower triad of states with similar C6 values correlating to the K (4 s) + Rb (5 p1/2) asymp-tote; and to five states in an upper triad of three states (3 (0+ ), 3 (0– ), 3 (1)) and a dyad of two states (4 (1), 1 (2)), with one set of similar C6 values within the upper triad and a dif-ferent set of similar C6 values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. ( J. Chem. Phys. 111, 8 857 (1999)), identifying three of our levels as v = 61, 62 and 63 of the 1 1Π ~ 4 (1) state they observed.

We also argue that ultracold photoassociation to levels between the K (4 s) + Rb (5 p3/2) and K (4 s) + Rb (5 p1/2) asymptotes may be weakly or strongly predissociated and there-fore difficult to observe by ionization of a 3Σ+ (or X 1Σ+ ) molecules; we do know from Kasahara et al. that levels of the 1 1Π ~ 4 (1) and 2 1Π ~ 5 (1) states in the intraasymptote region are predissociated. A small fraction (≤ 1/3) of the triplet (a 3Σ+ ) ultracold mole-cules formed are trapped in the weak magnetic field of our magneto-optical trap ( MOT ).

Work performed in collaboration with Professors Phil Gould, Ed Eyler and Warren Zemke, Drs. Steve Gensemer, Henry Wang, Jianbing Qi and Olga Nikolayeva, Dajun Wang, Mary Stone and Brian Hattaway.

Partial support by the National Science Foundation is gratefully acknowledged.

10

Cold Molecular Ion Studies in Traps

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MICHAEL DREWSEN

Institute of Physics and Astronomy, University of Aarhus, Ny Munkegade, Build. 520, DK-8000 Aarhus C, Denmark

In ion traps, the translational motion of molecular ions can effectively be sympathetically cooled to temperature in the mK regime through the Coulomb interaction with laser cooled atomic ions. At such low temperatures the molecular ions typically become part of spatial ordered structures, often referred to as Coulomb crystals, in which the individual molecules may be localized to within a few µm3 [1,2,3]. Since both the shape and the size of larger multi-component Coulomb crystals depend on the number as well as the charges and the masses of the ions present, any molecular ion processes which leads to a change in one (or more) of these quantities can be studied through observations of the change of the structure of a Coulomb crystal during an experiment [4]. The strong Coulomb interaction between trapped molecular ions and laser cooled atomic species furthermore makes it possible to conduct experiments using only a few or just a single molecular ion [2]. Since experiments with Coulomb crystals is normally performed at a vacuum of ~10–10 mbar, the typical collision times with background atoms and molecules is of the order of minutes. This makes Coulomb crystals unique for studies of very slow processes, including e.g. laser cooling of the rotational degrees of freedom of heteronuclear diatomic molecules [5].

Recently, we have focussed partly on experiments photo-dissociation studies of MgH+ molecules of relevance for future measuring the rotational temperature of rotationally cooled molecules [6], and partly on realizing a rather simple non-destructive scale (∆ m /m ≈ 10–4 ) which can be applied in connection with single molecular ion experi-ments [3].

[1] K. Mølhave and M. Drewsen: Phys. Rev. A 62, 011 401 (R) (2000) [2] M. Drewsen et al.: CP606, Non-Neutral Plasma Physics IV, Eds. F. Anderregg et al., p. 135 (2002) [3] M. Drewsen, A. Mortensen, R. Martinussen, P. Staanum, J. L. Sørensen: to appear in PRL [4] M. Drewsen et al.: Int. J. Mass Spec. 83, 229 (2003) [5] I. S. Vogelius, L. B. Madsen, M. Drewsen: Phys. Rev. Lett. 89, 173 003 (2002) [6] A. Bertelsen, I. S. Vogelius, S. Jørgensen, R. Kosloff, M. Drewsen: to appear in Eur. Phys. J. D

11

Photoassociation in an ultracold gas of metastable Helium

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J. LÉONARD, UMAKANT D. RAPOL, JAEWAN KIM, S. MOAL, M. WALHOUT, A. P. MOSK, M. LEDUC

Laboratoire Kastler Brossel and Ecole Normale Supérieure, Paris, France

Helium 4 atoms in the metastable 2 3S1 state ( He*), carry an internal energy of 20 eV, which is responsible for efficient ionizing collisions: the so-called Penning ionization. However, if the atomic gas is spin-polarized we observe a strong inhibition of the Penning collisions. That is why a spin-polarized gas of He* can undergo Bose Einstein Condensation ( BEC) after evaporative cooling in a magnetic trap [1]. I will discuss photoassociation ( PA) experiments recently performed at Ecole Normale Supérieure in this ultra-cold gas at temperatures in the µK range close to the BEC transition [2].

I will present giant helium dimers produced by exciting bound sates in a purely long range molecular potential with a PA laser beam red detuned from the 2 3S1 – 2 3P0 line at 1 083 nm [3]. For these previously unobserved states, the classical inner turning points are about 150 a0 and the outer ones as large as 1 150 a0; consequently the molecule destruc-tion by ionization is strongly suppressed, although the internal energy of these states is above 40 eV. Besides the huge internal energy of these dimers, one of the original fea-tures of our PA experiments is that the temperature of the cloud is used as a precise indicator of the molecular spectrum. Thanks to this » calorimetric « detection, the mole-cular ro-vibrational spectrum is measured with a great accuracy and gives an excellent agreement with theoretical predictions that only account for the dipole – dipole interaction and the atomic fine structure [4].

Other molecular states are observed in the red of the 2 3S1 – 2 3P2 line, which are not purely long range. The detailed comparison between our trap-loss measurement in Paris and the ion rate measurements in a Magneto-Optical Trap in Utrecht gives insight into the mechanism of the Penning ionization process [5]. All the resonances observed in Paris are identified. They correspond to molecules with a pure quintet spin character at short interatomic distances. This is the reason why the autoionization is inhibited. Only a weak rotational coupling is responsible for the contamination by singlet spin states, leading to a detectable ion signal in the Utrecht experiment.

[1] F. Pereira Dos Santos et al.: Phys. Rev. Lett. 86, 3 459 (2001), A. Robert et al.: Science 292, 463 (2001) [2] J. Kim et al.: Eur. Phys. J. D 31, 227 – 237 (2004) [3] J. Léonard et al.: Phys. Rev. Lett. 91, 073 203 (2003) [4] J. Léonard et al.: Phys Rev A 69, 032 702 (2004) [5] J. Léonard et al.: submitted for publication

12

Exploration of new Methods for Quantum Optics with Macromolecules

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MARKUS ARNDT

Institut für Experimentalphysik, Universität Wien, Boltzmanngasse 5, A - 1090 Wien

Molecule Interferometry with Macromolecules requires developments along various directions: source preparation, detection and coherent manipulation schemes. We will discuss the current state of the art, as well as short and long term perspectives.

13

Monday 21 February 2005

Introduction of the teams

(14.15 – 18.15)

Chair: Françoise Masnou

14.15 – 14.40 FHI Berlin Meijer / Vanhaecke – 16

14.40 – 15.05 Imperial Sauer / Mueller – 17

15.05 – 15.30 Jerusalem Kosloff / Jørgensen – 18

15.30 – 16.00 Orsay Theo. Masnou / Koch – 19

16.00 – 16.30 Coffee

16.30 – 16.55 Düss./Humb. Schiller / Blythe – 20

16.55 – 17.20 Pisa Gabanini / Lozeille – 21

17.20 – 17.45 Orsay Exp. Pillet / Mudrich – 22

17.45 – 18.00 Storrs Stwalley

18.00 – 18.15 Zagreb Pichler

15

Deceleration and electrostatic trapping of OH radicals

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N. VANHAECKE1, S. Y. T. VAN DE MEERAKKER1,2, G. MEIJER1,2

1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4 – 6, 4195 Berlin, Germany

2 FOM-Institute for Plasmaphysics » Rijnhuizen « , Edisonbaan 14, 3439 MN Nieuwegein, the Netherlands.

Over the last years our group has been developing methods to get improved control over the absolute velocity and over the velocity spread of molecules in a molecular beam. These methods rely on the, quantum state specific, force that polar molecules experience in homogeneous electric fields. This force is rather weak, but nevertheless suffices to achieve complete control over the molecular motion, and polar molecules in a supersonic beam can be brought to rest and confined in an electrostatic trap.

Here, we report on the deceleration and electrostatic trapping of ground state O H radicals. The experiments are performed in a new generation molecular beam decelera-tion machine, designed such that a large fraction of the molecular pulse can be slowed down and trapped. Depending on the details of the trap loading sequence, typically 105 OH ( X2 Π 3/2, J = 3/2) radicals are trapped at a density of 107 cm–3 and at a tempera-ture in the 50 – 500 µK range. In our deceleration experiments, state-selective molecular beams with a computer controlled velocity distribution are produced, offering the unique possibility to perform collision reactive scattering experiments as a function of the continuously tunable collision energy and with unprecedented energy resolution.

16

Production of cold molecular radicals by laser ablation and supersonic expansion – A study

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T. MUELLER, R. V. DARNLEY, M. R. TARBUTT, J. J. HUDSON, B. E. SAUER, E. A. HINDS

Centre for Cold Matter, Department of Physics, Imperial College London, SW7 2BW

Supersonic expansion is a well-established method for producing cold molecular beams. A gas at high pressure expands through a nozzle into a vacuum chamber thereby cooling to a low temperature, typically 1 K. Most molecules of interest have an insuffi-cient vapour pressure to be introduced directly into the carrier gas, but can instead be introduced by laser ablation of a suitable target. By ablating Yb and Ca targets and adding a small fraction of SF6 to the carrier gas, we have successfully produced cold beams of the radicals YbF and CaF [1].

While this technique has proven successful for a wide variety of molecular species, some widely-recognized problems remain. What limits the number of molecules pro-duced ? Why is the molecular flux higher with some carrier gases than with others ? What limits the shot-to-shot stability and why does the flux of molecules decay as the target ages ?

We have recently begun to address some of these important issues. We are studying the formation of molecular radicals and aspects of target lifetime when various targets are ablated inside a buffer gas cell. We have also studied clustering within the supersonic expansion using a Rayleigh scattering technique, and have determined both the shot-to-shot and long term behaviour of our cold molecule source with respect to the energy in the ablation pulse and other critical parameters. We will present our findings.

[1] M. R. Tarbutt, J. J. Hudson, B. E. Sauer, E. A. Hinds, V. A. Ryzhov, V. L. Ryabov, V. F. Ezhov: J. Phys. B 35, 5 013 (2002)

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Rotational state detection and rotational cooling of Mg H+ ions

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S. JØRGENSEN1, A. BERTELSEN1, M. DREWSEN1, R. KOSLOFF2

1 Department of Physics and Astronomy, University of Aarhus, DK - 8000 Aarhus C, Denmark

2 Department of Physical Chemistry, the Hebrew University, Jerusalem 91904, Israel

An ion Coulomb crystal is a spatially ordered structure that appears when ions are laser-cooled to a temperature of a few milli Kelvin. Molecular ions can be embedded in a Coulomb crystal sympathetically cooling via Coulomb interactions with the laser-cooled host ions. In such a situation, the molecular ions are translationally cold (T < 10 mK) and can be spatially extremely well-localized (~10 µm3) [1,2]. Internally, the interactions with the black-body radiation field in the trap region is often expected to leave the molecular ions in the vibrational ground state, but with population of several rotational states. When dealing with molecular ions in Coulomb crys-tals several interesting questions, however, emerge: Do the rotational degrees of freedom cool through the interaction with the laser-cooled atomic ions ? If not, are there ways to cool them ?

In this talk we consider MgH+ ions embedded in Coulomb crystal of Mg+ ions. The rotational temperature of MgH+ depends on the sympathetical cooling strength from the laser-cooled ions through Coulomb interaction. The stronger the sympathetical cooling strength becomes the MgH+ ions get colder. The rotational temperature of MgH+ has been determined by State-selective Two-photon resonant Enhanced Photo-dissociation (STEP) process with nanosecond pulses [3].

Absorption of the first photon drives a resonant rotational excitation from a rotational state in the electronic ground state, X 1Σ+ to a rotational state in the excited state A 1Σ+. From A 1Σ+ the molecule can either decay spontaneously to any rovibrational state of the ground electronic state or absorb a second photon, then it is excited into a non-binding electronic state, C 1Σ+, and the molecule dissociates. In between the two excitation pulses the molecule relaxes its rovibration levels due to black body radiation in the trap and interaction with the laser cooled Mg+ ions. The idea is, that if the resonant excitation is saturated by the photon field, then the resonant dissocia-tion process is more effective than the direct off resonant dissociation process. Hence, the disso-ciation rate depends on the population of rotational state from which the resonant excitation occurs, the rotational temperature can, therefore, be extracted. We have shown that the rotational temperature of MgH+ is above 100 K indicating a weak or no sympathetical rotational cooling from the laser-cooled Mg+ ions.

Our next aim is cooling of the rotational degree of freedom of the MgH+ ions. Several cooling schemes have been proposed [4,5]. Here, we will consider a broad band laser [5] where the dark state corresponding to the electronic transition X 1Σ+(v = 0 , J = 0) to A 1Σ+(v = 0 , J = 1) has been filtered out. This pulse is short and has a weak intensity such that the possibility of dissociation is small. The excited molecular ion will decay by spontaneous emission to the elec-tronic ground state. The molecules which reach the lowest rotational state by spontaneous emission are trapped.

[1] K. Mølhave and M. Drewsen: Phys. Rev. A 62, 011 401 (2000) [2] M. Drewsen et al.: Phys. Rev. Lett. 93, 243 201 (2004) [3] A. Bertelsen et al.: Eur. Phys. J. B 31, 403 (2004) [4] I. Vogelius, L. B. Madsen, M. Drewsen: Phys. Rev. Lett. 89 173 003 (2002); Phys. Rev. A 70, 053 412 (2004) [5] A. Bartana, R. Kosloff, D. Tannor: Chem. Phys. 267, 195 (2001)

18

Formation of ground state cold molecules via optical Feshbach resonances.

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CHRISTIANE P. KOCH1,2, RONNIE KOSLOFF2, FRANÇOISE MASNOU-SEEUWS1

1 Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France

2 Department of Physical Chemistry, the Hebrew University, Jerusalem 91904, Israel

We propose to create ground state molecules by adiabatic crossing of an optical Fesh-bach resonance. At present, molecules are created in cold quantum gases by sweeping magnetic Feshbach resonances, tuning the magnetic field strength. This is possible for systems with hyperfine structure splitting where such resonances are present at conven-ient magnetic field strengths. Optical Feshbach resonances are more generally available. They can be found at various laser frequencies by coupling to vibrational levels of the electronically excited states. They offer more flexibility since two parameters, the intensity and the frequency of the laser, can be tuned simultaneously. The drawback is loss due to spontaneous emission which should be minimized.

In the present work, we start from a pair of atoms in the lowest level of a tight optical trap and we propose adiabatic ramping over an optical Feshbach resonance, tuning both intensity and frequency. The resulting atom pair wave function has components on both electronic ground and excited states. At a certain intensity and detuning, the ground state part is pushed below the dissociation limit which corresponds to forming bound mole-cules. The excited state part is subject to spontaneous emission losses. In a second step, the laser field therefore needs to be switched off. This corresponds to projecting the wave function onto the field-free eigenstates. Our calculations are performed for 87Rb atoms, for transitions from both a 3Σu

+ and X 1Σg+ ground state potentials. We show that for

sufficiently tight traps (ν ≥ 50 kHz), adiabaticity can be retained without loss by spontaneous emission. Up to 50 % of the population can then be transferred to the last vibrational levels of the ground state. A related phenomenon of creating ground state molecules has been discussed in Ref. [1].

[1] E. Luc-Koenig, R. Kosloff, F. Masnou-Seeuws, M. Vatasescu: Phys. Rev. A 70, 033 414 (2004). E. Luc-Koenig, M. Vatasescu and F. Masnou-Seeuws: Eur. Phys. J. D 31, 239 (2004).

19

Towards spectroscopy of sympathetically - cooled HD+

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PETER BLYTHE, BERNHARD ROTH, ULF FRÖHLICH, HELMUT WENZ, STEPHAN SCHILLER

Institut für Experimentalphysik, Universität Düsseldorf

Cold, trapped, simple molecules offer the prospect of precision tests of fundamental theories by high-resolution optical spectroscopy. The simplest molecule, the hydrogen molecular ion, is our chosen spectroscopic target, as its energy levels may be calculated to a very high degree of accuracy from first principles. In particular, the transition frequencies depend on the electron-proton mass ratio me /mp. By spectroscopy of the 1.4 - micron vibration transition in cold HD+, we hope to make an accurate measurement of this mass ratio, and in further experiments, to set an upper limit on its possible time-variation.

The first step towards this, the production of large samples of HD+ (along with several other molecular hydrogen isotopomers) at temperatures of a few tens of milli-Kelvin, has recently been achieved, and these results will be presented at the meeting. The molecular ions are sympathetically cooled by laser-cooled beryllium ions in a linear ion trap, and a large variety of two- and three-component cold ion crystals have been produced and studied in detail experimentally and by molecular dynamics simulations. The spectroscopic system and detection techniques are under development, and progress and prospects in these areas will be described at the meeting.

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Experiments and simulation on cold Rubidium dimers

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JÉRÔME LOZEILLE

IPCF - CNR, Via Moruzzi 1, I - 56124 Pisa

A summary of the experiment of formation, trapping and detection of rubidium dimers is presented. Translationally cold molecules have been recorded in MOT and observed in a dipolar trap. Preliminary work is presented for the analysis of the observed multiphoton ionization spectrum of the 87Rb2 dimer.

21

Optical Trapping of Ultracold Cs2 Molecules M

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MARCEL MUDRICH, NASSIM ZAZHAM, THIBAULT VOGT, DANIEL COMPARAT, PIERRE PILLET

Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France contact: pierre.pillet @ lac.u-psud.fr

The extension of the cooling and trapping techniques developed for ultracold atoms to ultracold molecules has attracted great interest in the past years [1]. Main goals are ex-ploring the rich collisional physics in a gas of molecules and in atom – molecule mixtures in the ultracold regime such as vibrational and rotational quenching and the measurement of lifetimes of metastable molecular states such as the a 3Σu

+ state in alkali dimers.

22

Fig. 1.: Storage time measurements of Cs atoms in the hyperfine ground states F = 3 and F = 4 and of Cs2 molecules in a mixture of Cs2 and Cs in F = 4. The molecules are formed inside the CO2 laser trap from pairs of atoms in F = 4 by photo-association to the 0g–, v = 6 excited molecular state and spontaneous emission. Both atoms and molecules are detected by photoionization.

We present storage time measurements of Cs2 molecules in a quasi-electrostatic trap (QUEST ) formed by the focus of a 130 W CO2 laser, as it has been demonstrated before for Cs2 [2] and Rb2 [3]. This type of trap is particularly well suited since both atoms and molecules are trapped in any internal state and heating due to photon scattering is negligi-ble. In our experiment, Cs2 molecules are formed by photoassociation inside the QUEST and both atoms and molecules are detected by resonance enhanced two-photon ioniza-tion. The storage time for Cs atoms in the lowest hyperfine state F = 3 of τ = 3.4 s is limited by the background gas pressure of 4 · 10–10 mbar. Fast trap loss of Cs2 is observed in a mixture of Cs and Cs2 resulting from inelastic collisions. Atom – molecule and molecule – molecule inelastic collision rates are inferred for various combinations of atomic hyperfine states and molecular ro-vibronic state distributions.

[1] J. Doyle, B. Friedrich, R. V. Krems, F. Masnou-Seeuws: Eur. Phys. J. D 31, 149 (2004) [2] T. Takekoshi, B. M. Patterson, R. J. Knize: Phys. Rev. Lett. 81, 5 105 (1998) [3] A. Fioretti, J. Lozeille, C. A. Massa, M. Mazzoni, C. Gabbanini: » An optical trap for cold rubidium molecules «

submitted (2004)

Monday 21 February 2005

Evening Talk

(19.30 – 20.30)

Chair: Eberhard Tiemann

23

BEC and more exciting physics with ultracold molecules

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RUDI GRIMM

Institute of Experimental Physics, Innsbruck University,

Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Innsbruck, Austria

www.ultracold.at

The physics of ultracold molecules has become a very exciting and vibrant research field. The world’s coldest molecular samples are produced in the nanokelvin range by association of molecules from ultracold gases of atoms through magnetically induced Feshbach resonances. After giving a general survey of this field, I will report on two different research lines pursued in Innsbruck.

Starting with an ultracold gas of fermionic 6Li atoms, we produce weakly bound dimers which are extremely stable against inelastic decay. We show that the gas can be evaporatively cooled down to Bose-Einstein condensation [1]. Based on the molecular BEC we investigate the crossover to a BCS-type superfluid by Feshbach tuning of the scattering length. We find strong evidence for resonance superfluidity in the strongly interacting regime [2].

In a second experiment, we start with an atomic BEC of cesium and produce weakly bound cesium dimers through a Feshbach ramp [3]. We can trap an ensemble of more than 10 000 molecules in a CO2 laser trap. By specific changes of the magnetic field we can transfer the weakly bound dimers into different ro-vibrational quantum states using weak avoided level crossings. We explore the magnetic-field dependent collision proper-ties of the weakly bound molecules. A tantalizing observation is the occurrence of resonance features, which we interpret as a result of resonant coupling to Cs4 tetramer states [4]. This may open up a new route to the realm of ultracold molecule physics beyond dimers.

[1] S. Jochim et al.: Science 302, 2 101 (2003) [2] C. Chin et al.: Science 305, 1 128 (2004) [3] J. Herbig et al.: Science 301, 1 510 (2003) [4] C. Chin et al.: cond-mat/0411 258

25

Tuesday 22 February 2005

Introduction of the teams

(8.15 – 9.55)

Chair: Gerard Meijer

08.15 – 08.40 Austrap Grimm / Kraemer – 28

08.40 – 09.05 Hann./Freib. Tiemann / Staanum – 29

09.05 – 09.30 Roma Gianturco / Bodo – 30

09.30 – 09.55 Utrecht v. d. Straten / Nehari – 31

27

News on ultracold Cs2 dimers T

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T. KRAEMER1, M. MARK1, J. HERBIG1, P. WALDBURGER1, C. CHIN1, H.-C. NAEGERL1, R. GRIMM1,2

1 Institut für Experimentalphysik, Universität Innsbruck, 6020 Innsbruck, Austria 2 Institut für Quantenoptik und Quanteninformation,

Österreichische Akademie der Wissenschaften, 6020 Innsbruck, Austria

We investigate dynamics and interactions of Cs2 dimers in a CO2-laser dipole trap. Starting with a Bose-Einstein condensate ( BEC) of 2.2 · 105 Cs atoms, we create ultracold molecules in a single, weakly bound quantum state by sweeping the magnetic field across a narrow Feshbach resonance. When the molecules are created in free space, the conversion efficiency exceeds 30 %, yielding up to 40 000 molecules [1]. In our trapping experiments, about 6 000 ultracold Cs2 dimers are prepared in the optical trap at a temperature of 200 nK. We transfer the trapped molecules from the initial molecular state to other molecular states by following avoided crossings. We find two magnetically tunable resonances in collisions between the molecules for one of the molecular states. We interpret these Feshbach-like resonances as being induced by Cs4 bound states near the molecular scattering continuum [2]. Further, we have discovered a new molecular state with very large orbital angular momentum of l = 8. This state is very weakly coupled to one of the initial molecular states. We use the associated avoided crossing as a molecular beam splitter to realize a molecular Ramsey-type interferometer. The interferometric signal is shown in Fig. 1.

Fig. 1: Molecular interferometer at nanokelvin temperatures. Top: One full oscillation period between two different molecular states which give rise to different spatial distributions upon dissociation. Bottom: Population in the central peak as function of time. The contrast is about 60 %.

We acknowledge support by the Austrian Science Fund (FWF) within SFB 15 and by the European Union in the frame of the Cold Molecules TMR network under Contract HPRN-CT-2002-00290.

[1] M. Mark, T. Kraemer, J. Herbig, H.-C. Nägerl, R. Grimm: cond-mat/0409 737 [2] C. Chin, T. Kraemer, M. Mark, J. Herbig, P. Waldburger, H.-C. Nägerl, R. Grimm: cond-mat/0411 258.

28

Studies of ultracold Cs2 and LiCs molecules

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PETER STAANUM

Institute of Physics, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany

In the scientific part of the presentation we present the current status of our experi-ments which aims at forming and studying ultracold Cs2 and LiCs molecules. Cs2 mole-cules in the a 3Σg

+ state are formed by photoassociation and state-sensitively detected using two-photon ionization and time-of-flight mass spectrometry. The Cs2 molecules are trapped in an optical dipole trap formed by the focus of a CO2 laser. The optical dipole trap enables simultaneous trapping of atoms and molecules and hence facilitates studies of atom – molecule collisions and molecule-molecule collisions. Here we present results on Cs – Cs2 collisions.

For the future experiments on formation of LiCs by photoassociation, we have devel-oped a time-of-flight mass spectrometer for experiments with ultracold atoms and mole-cules. The spectrometer has a mass resolution of 500 (m /∆ m at the Cs mass), which enables us to resolve the nearby LiCs and Cs peaks in the time-of-flight spectrum and hence to unequivocally detect LiCs. A sample of optically trapped LiCs atoms enables studies of the interaction between the highly polar LiCs molecules and electric fields as well as studies of collisions between LiCs and other atoms or molecules.

In parallel, Lis molecules formed in a heat pipe will be studied spectroscopically using the laser induced fluorescence technique combined with Fourier transform spectroscopy which already was successfully applied to other heteronuclear alkali dimers.

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Cold reactions involving ionic partners: preliminary results on the He3+ system

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E. BODO

Department of Chemistry, The University of Rome » La Sapienza « , Piazzale A. Moro 5, 00185 Rome, Italy

With the development of techniques for the storage of ultra-cold molecules and for the construction of cold molecular beams, the study of chemical reactions at temperature near T = 0 might become feasible.

Dynamics of atoms and molecules at ultra-low kinetic energies is dominated by quan-tum effects. In this regime, inelastic processes (including exoergic chemical reactions) can be dominant over elastic scattering because the corresponding cross section depends on the inverse of the initial relative velocity.

We have already analyzed benchmark chemical reaction at ultra-low energies [1] and we have also investigated the effect of internal excitation in reactants molecules [2,3]. We will briefly discuss some preliminary results involving calculations for inelastic and reactive processes in the ionic systems He3+ [4].

[1] E. Bodo, A. Dalgarno, F. A. Gianturco: J. Chem. Phys. 116, 9 222 (2002) [2] E. Bodo, F. A. Gianturco, A. Dalgarno: J. Phys. B 35, 2 391 (2002) [3] E. Bodo and F. A. Gianturco: Eur. Phys. J. D 31, 423 (2004) [4] E. Scifoni, E. Bodo, F. A. Gianturco: Eur. Phys. J. D 30, 363 (2004)

30

Photoassciation of cold metastable Helium atoms: from 1 to 2 color transition

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D. NEHARI, H. PORTE, P. VAN DER STRATEN

Debye Institute, Department of Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80 000, 3508 TA Utrecht, The Netherlands

We have studied photoassociation of metastable 2 3S helium atoms near the 2 3S – 2 3P2 asymptote by both ion detection in a magneto-optical trap and trap loss measure-ments in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The same setup is used to study the photoassociation of metastable 2 3S helium atoms near the 2 3S – 2 3P1 and 2 3S – 2 3P0 asymptotes by ion detection in a MOT.

Recently, we started to study the two color process in order to measure the spectrum of the ro-vibrational states correlated to the 2 3P – 2 3P asymptote. Since the second transition to reach this higher asymptote corresponds to a bound-bound transition, the excitations probabilities are much weaker than the ones corresponding to the transition from the free states of 2 3S – 2 3S asymptote to the bound states of the 2 3S – 2 3P2,1,0

asymptotes. We are still improving the conditions of the measurements to detect the bound states of the 2 3P – 2 3P asymptote. In addition, we observe a polarization effect of the probe laser used to associate the two metastable helium atoms, the peaks positions corresponding to the bound states remain the same but the line shape of these peaks are different from a polarization to an other. Because of the unpolarized atoms trapped in the MOT and the very weak magnetic field at its position, this polarization effect remain unexplained till now. The preliminary results are presented and discussed in my talk and poster.

31

Tuesday 22 February 2005

Contributed Talks

(14.00 – 16.00)

Chair: Matthias Weidemüller

14.00 – 14.15 David Carty – 34

14.15 – 14.30 Christian Lisdat – 35

14.30 – 14.45 Peter Schmelcher – 36

14.45 – 15.00 Stephan Schiller – 37

15.00 – 15.15 Goran Pichler – 38

15.15 – 15.30 Johnny Vogels – 39

15.30 – 15.45 Olivier Dulieu – 40

15.45 – 16.00 Gerald Auböck – 41

33

A Sectional Storage Ring for Neutral Molecules T

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DAVID CARTY1,2, HENDRICK L. BETHLEM2,3, CYNTHIA E. HEINER1, FLORIS M. H. CROMPVOETS3, GERARD MEIJER2

1 Chemistry Research Laboratories, University of Oxford, Oxford, UK 2 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

3 FOM-Institute for Plasma Physics » Rijnhuizen «, Nieuwegein, The Netherlands

It has been shown previously that a package of ultracold (ca. 250 µK) ND3 molecules, produced via an injection beam-line consisting of a Stark decelerator [1], can be stored in a 25 cm diameter toroidal hexapole trap for more than 50 ring traversals, corresponding to an observable trapping time of ca. 300 ms [2]. Whilst the package of molecules was transversally confined, the finite tangential velocity spread meant that the originally small package of molecules had a propensity to stretch out. Eventually the package filled up the entire ring and became too dilute to observe.

A prototype for the second generation of storage ring has been designed to counter-act this propensity for the package to spread out by making it sectional with the inclusion of two »bunching« elements inside the ring. These bunchers keep the package of mole-cules together by giving the slower moving molecules lagging behind a slight acceleration whilst giving the faster moving molecules advancing ahead a slight deceleration. In this way the package will be confined longitudinally as well as transversally and the number of observable round trips, and therefore trapping time, will be greatly increased.

We report here on the functionality and operation of a prototype sectional storage ring. It will also be shown, through the use of numerical trajectory calculations, that such a ring is feasible and should be capable of trapping ultracold neutral molecules for times significantly longer than previously demonstrated.

[1] Floris M. H. Crompvoets, Rienk T. Jongma, Hendrick L. Bethlem, André J. A. van Roij, Gerard Meijer: Phys. Rev. Lett. 89, 093 004 (2004)

[2] Floris M. H. Crompvoets, Hendrick L. Bethlem, Jochen Küpper, André J. A. van Roij, Gerard Meijer: Phys. Rev. A 69, 063 406 (2002)

34

Towards Stark deceleration of SO2 to investigate its cold photofragmentation

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CH. LISDAT, S. JUNG, G. MEIJER∗, E. TIEMANN

Institut für Quantenoptik, Universität Hannover, Germany www.iqo.uni-hannover.de, lisdat @ iqo.uni-hannover.de

Cold and ultracold gases allow for the study of interparticle interactions under well determined experimental conditions, since only a limited number of quantum mechanical channels are populated. This situation offers especially for molecules the possibility to explore reactions in a quantum state specific way. We will add the SO2 molecule to the possible candidates for such experiments.

Sulphurdioxide has versatile applications in this field. One very intriguing property is, that this molecule can be the source of new cold particles itself, which are SO and O. The fragments are generated by photodissociation and show low excess energy [1]. Both particles are free radicals that can be used as cold reactants in further experiments. On the other hand, the dissociation process close to the threshold is interesting to investi-gate. The threshold behaviour is likely tuneable by external fields and shows great similarity to Feshbach resonance studies in cold atom collisions.

ener

gy [c

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-1

SO2 SO( ) + O( P )3 - 3Σ 2

J N

5 4

4 3

3 2

2 11 00 1

45750

45745

45740

45735

45730

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45720

725634707

716

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E ~ 850 mKkin E ~ 187 mKkin

D0

0 ~X A1

1

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- 214

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616

505

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2 ~ X Σ

40000

734

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The source of cold SO2 will be a Stark decelerat

varying inhomogeneous fields on the dipole momendecelerator of this type will consist of a large numbhigh mass and comparably small Stark effect of SO2.the feasibility of a decelerator for SO2 and experimmanipulation of SO2 trajectories by an electrostatic h

∗ Fritz-Haber-Institut of the Max-Planck-Gesellschaft, Berl[1] S. Becker, C. Braatz, J. Lindner, E. Tiemann: Chem. Phys. L[2] H. Bethlem, G. Meijer: Int. Reviews in Physical Chemistry

Excerpt of the level scheme of SO2 and the dissociation fragment SO. Some dissociation channels with low excess energy are shown.

or [2], which uses the force of time-t of a molecule to slow it down. A er of deceleration stages due to the

We will present simulations showing ental results of the first successful

exapole lens.

in ett. 208, 15 (1993)

22, 73 (2003)

35

Rovibrational Dynamics of Heteronuclear Diatomics in Strong Electric Fields

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R. GONZALEZ1 AND P. SCHMELCHER2,3

1 Departamento de Física Moderna and Instituto, » Carlos I « de Física Teórica y Computacional, Universidad de Granada, E - 18071 Granada, Spain

2 Physikalisches Institut, Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany

3 Theoretische Chemie, Universität Heidelberg, INF 229, 69120 Heidelberg, Germany

We investigate the rovibrational dynamics of heteronuclear diatomic molecules ex-posed to a strong external static and homogeneous electric field focusing on systems with a 1Σ+ electronic ground state.

Using a hybrid computational technique combining discretisation and basis set meth-ods the full rovibrational equation of motion is solved. As a specific example the rovibra-tional spectrum and properties of the carbon monoxide molecule are analyzed for experi-mentally accessible field strengths. Results for energy levels, expectation values and rovibrational spectral transitions are presented. They indicate that while low-lying states are not significantly affected by the field, for highly excited states strong orientation and hybridization are achieved.

We propose an effective rotor Hamiltonian, including the main properties of each vibrational state, to describe the influence of an electric field on the rovibrational spectra of a molecular system. The validity of this approach is illustrated by comparison with the results obtained with the fully coupled rovibrational Schrödinger equation. We thereby demonstrate that it is possible to create state-dependent hybridization of a molecular system, which is of importance for vibrational state-selective chemical reactions. This state-dependence is individually different for each molecular system and represents therefore a characteristic feature of the species. For stronger fields and particularly for the cold molecular alkali heterodimers it is possible to enter another regime that is characterized by an induced adiabatic coupling among the vibrational and hybridized rotational motions. Exact results are compared to the predictions of the newly developed adiabatic rotor approach as well as to the previously established effective rotor approxi-mation.

A detailed analysis of the impact of the electric field is performed: the hybridized and oriented rotational motion, the mixing of angular momenta and the squeezing of the vibrational motion are observed. It is demonstrated that these effects can well be ac-counted for by the adiabatic rotor approximation. References: 1) R. Gonzalez and P. Schmelcher:

Rovibrational Spectra of Diatomic Molecules in Strong Electric Fields: The Adiabatic Regime, Phys. Rev. A 69, 023 402 (2004)

2) R. Gonzalez and P. Schmelcher: Electric Field-Induced Adiabaticity in the Rovibrational Dynamics of Heteronuclear Diatomic Molecules, subm. f. publication to Phys. Rev. A

36

Cold Molecular Ions in RF Traps: Results and Perspectives

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B. ROTH, U. FRÖHLICH, P. BLYTHE, A. OSTENDORF, H. WENZ, S. SCHILLER

Institut für Experimentalphysik, Universität Düsseldorf

We give an overview of our experiments on sympathetic cooling and trapping of molecular and atomic ions. Our two apparata use beryllium and barium ions, respectively, for cooling other ionic species.

Species cooled so far are the hydrogen molecular ion isotopes, the helium isotopes, beryllium hydrides, argon, oxygen and carbon dioxide. Work towards trapping and cooling of organic and in particular large biomolecular ions is in progress.

The talk will discuss issues such as kinetic temperature of sympathetically cooled particles, identification via mass spectrometry, structural elucidation, purification, and chemical reactions.

37

Recent experiments with femtosecond laser and alkali metal vapor

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TICIJANA BAN, DAMIR AUMILER, GORAN PICHLER

Institute of Physics Bijenicka cesta 46, HR -10000 Zagreb, Croatia

I would like to report the observation of cone emission generated when ~10 nJ, 100 fs laser pulses in 730 – 2 770 nm wavelength range are transmitted through a dense cesium vapor. The spatial and spectral characteristics of the observed cone emission were studied experimentally. Cone angle dependence on the laser wavelength, laser average power and Cs atomic and molecular concentrations was investigated. The cone emission (CE) was only observed when the laser beam self-focused after passing through the medium. Several characteristics of the CE obtained in this experiment, such as the laser wavelength range in which it appears, large CE spectral blue detuning and high laser-CE energy conversion, are quite unique for femtosecond laser induced CE. In short we established that the cone emission in the case of dense cesium vapor is most probably of molecular origin. We observed cone emission in the case of rubidium and potassium, but effects were not so pronounced as in cesium case.

At room temperature and slightly elevated temperatures we studied the effect of trans-mission of the narrow c.w. laser scanned over the hyperfine structure of the rubidium D2 resonance line in the presence of the Ti:Sa femtosecond laser oscillator line centered at 780 nm. By scanning c.w. with 1 MHz width we observed interesting oscillations in its transmission spectrum, with peaks separated like within the frequency comb of the femtosecond laser oscillator. The phenomenon has been also studied in magnetic field and with different peak values of the femtosecond laser.

Quite recently we obtained RbCs all sapphire cell with Brewster windows, which can be heated to high vapor temperatures. We hope to observe triplet satellite bands and diffuse bands for the RbCs heteronuclear molecule in the absorption spectrum. Diffuse bands may be used for the detection of the ultracold RbCs molecules.

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Realization of a Magnetically Guided Atomic Beam in the Collisional Regime

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J. M. VOGELS, T. LAHAYE, K. J. GÜNTER, Z. WANG, J. DALIBARD, D. GUÉRY-ODELIN

Laboratoire Kastler Brossel, 24 rue Lhomond, F - 75231 Paris Cedex 05, France

We describe the realization [1] of a magnetically guided beam of cold rubidium atoms, with a flux of 7×109 atoms/s, a temperature of 400 µK, and a mean velocity of 1 m/s, see Figure 1. The rate of elastic collisions within the beam is sufficient to ensure thermaliza-tion. We show that the evaporation induced by a radio-frequency wave leads to apprecia-ble cooling and an increase in the phase space density. We discuss the perspectives to reach Bose Einstein Condensation using evaporative cooling on the beam.

[1] T. Lahaye, J. M. Vogels, K. J. Günter, Z. Wang, J. Dalibard, D. Guéry-Odelin: Phys. Rev. Lett. 93, 093 003 (2004)

39

Calculation of permanent and transition dipole moments of dipolar molecules

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M AYMAR AND O. DULIEU

Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France

The obtention of ultracold samples of dipolar molecules is a current challenge which requires an accurate knowlege of their electronic properties to guide ongoing experi-ments. Using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets and effective core polarisation potential, we investigate the properties of homonuclear and heteronuclear alkali dimers emphasiz-ing on convergence and accuracy issues with respect to the size of the basis sets and the details of effective potentials.

We will present several studies currently in progress: The first set of results concerns the permanent dipole moments of the ground and

lowest triplet states of all mixed alkali pairs. We will display their variation with the interatomic distance as well as with the vibrational level. Most of the results were not previously available elsewhere.

The second set results concerns transition dipole moments for alkali pairs under investigation in various spectroscopic studies, or in cold molecule experiments. Finally, in the perspective of photoassociation of cold francium atoms, we will present a prelimi-nary study of the pseudopotential for the francium atom, whose knowledge is prerequi-site to the determination of molecular potential energy curves. The inclusion of relativistic effects is under study.

40

Trap Loss Collisions in a Two - Species Na - Li Magneto - Optical Trap

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G. AUBÖCK, C. BINDER, L. HOLLER, J. SZCZEPKOWSKI, C. RUMPF, V. WIPPEL, W. E. ERNST, L. WINDHOLZ

Institut for Experimental Physics, Technical University of Graz Petersgasse 16, A - 8010 Graz (contact: windholz@ tugraz.at)

Soon after invention of the MOT it was found, that cold collisions of atoms in the presence of the MOTs near resonant laser light lead to trap losses. Two processes which transfer energy from the light field to kinetic energy of the colliding atoms were identi-fied: Radiative escape ( R E) and fine structure changing collisions ( FSC) [1]. Since then a lot of experimental and theoretical work was done on this topic, most of it investigating collisions between the same kind of atoms (an extensive review is given in [2]). The rate coefficients for trap loss collisions were found to be extremely sensitive to the long range behaviour of the potential energy curves of the colliding atom pair.

We investigated trap loss collisions of 23Na with 6Li and 7Li in a two-species MOT. The measurements were performed by studying Li decay curves after blocking the atomic beam which loads the Li MOT. From comparison of such decay curves with and without Na being loaded to a second, spatially overlapped MOT, trap loss rate coefficients for processes of the type

Li + Na + h ν1 → Li* Na → Li + Na + h ν2 + Ekin

were obtained and systematically investigated by varying the intensity of the Li MOT cooling laser light. The measurements require good vacuum conditions ( better than 10–10 mbar) to reduce trap losses due to collisions with hot background gas atoms. Only processes where a Li*Na quasimolecule is excited can lead to such trap loss processes since all potential energy curves asymptotically connecting to Li Na* are repulsive at large internuclear distances. We can interpret our measurements assuming that R E and FSC take place. However, we expect major differences to homonuclear trap loss collisions due to the much shorter range of the excited state potentials (this is particularly true for NaLi where the C6 coefficients are smaller than for all other heteronuclear combinations of alkali atoms). Furthermore we found astonishing large differences of the collisional trap loss rates for 6Li – Na and 7Li – Na. We believe this demonstrates the important role of hyperfine structure for heteronuclear trap loss collisions.

[1] A. Gallagher and D. E. Pritchard: Phys. Rev. Lett. 13, 452 (1988) [2] J. Weiner, V. S. Bagnato, S. Zilio, P. S. Julienne: Rev. Mod. Phys. 71, 1 (1999)

41

Tuesday 22 February 2005

Poster Session

(16.00 – 18.30)

The following section does not include abstracts of posters being complimentary to oral contributions during this workshop.

A complete list of posters is given on page 7.

43

Interactions between 1S and 3P calcium atoms: study for cold molecule formation.

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O. ALLARD1, ST. FALKE1, A. PASHOV1, O. DULIEU2, H. KNÖCKEL1, E. TIEMANN1

1 Institut für Quantenoptik, Universität Hannover, Welfengarten 1, 30167 Hannover 2 Institute for Scientific Research in Telecommunications,

ul. Hajdushka Poliana 8, 1612 Sofia, Bulgaria 3 Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France

Transitions of the Ca2 A 1Σu+ – X 1Σg

+ system are observed in a LIF experiment com-bined with high-resolution Fourier-transform spectrometry. Term energies of the per-turbed A 1Σu

+ state levels are constructed using the well known X 1Σg+ ground state [1,2].

We performed a depertubation analysis considering a model, which is complete within the A 1Σu

+, c 3Πu , and a 3Σu+ subspace of relevant neighboring states, in order to derive

diabatic (with respect to the spin-orbit and rotation interaction) potential curves and R-dependent spin-orbit coupling directly from measured transition frequencies. eigen-energies of this coupled system are calculated employing the Fourier grid Hamiltonian method.

Our analysis leads to a representation very close to the experimental uncertainty. The Ω = 0+ and one Ω = 1 component of the system A 1Σu

+, c 3Πu , and a 3Σu+ are correlated

to the asymptote 1S0 + (4s 4p) 3P1 and hence describe cold collisions of atoms with these states, which are of interest for an optical frequency standard on the intercombination line of Ca. Moreover, predictions of ultra cold molecule formation rates can be deter-mined. The wave functions of the coupled state levels are calculated from the derived potentials and coupling strengths. The branching ratios of these levels, which are reach-able via photoassociation, to the vibrational levels of the ground state are derived. Our interest is to investigate the influence of the triplet-singlet mixing on the formation of ultra cold molecules.

[1] O. Allard et al.: Phys. Rev. A 66, 042 503 (2002) [2] O. Allard et al.: Eur. Phys. J. D 26, 155 (2003)

44

Ultracold collision dynamics involving molecular systems

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E. BODO AND F. A. GIANTURCO

Department of Chemistry, The University of Rome » La Sapienza « , Piazzale A. Moro 5, 00185 Rome, Italy

Dynamics of atoms and molecules at ultra-low kinetic energies is dominated by quantum effects. At such energies the scattering of an atom molecule system is domi-nated by the S-wave component when the relative angular momentum is zero. In this regime, inelastic processes can be dominant over elastic scattering because the corres-ponding cross section depends on the inverse of the intial relative velocity. There are currently various methods which are employed to produce and trap cold molecules: photo-association of ultra-cold atoms, deceleration of molecules through an array of time-varying inhomogeneous electric fields, injection of the molecules in a cold He buffer and, finally, promotion of a conversion between an atomic Bose or Fermi gas into a molecular Bose gas by tuning a Feshbach resonance using magnetic fields. With the development of techniques for the construction of slowly moving crossed molecular beams, experiments might become feasible to study chemical reactions where the rates are faster than the decay of the cold molecule ensembles that arises from trap losses [1]. This condition is not readily satisfied for ground state molecules because most of the reactions exhibit a barrier along the reaction path that, when the kinetic and internal energies are very low, drives the reaction to proceed by quantum tunneling of the exchanged atom [1]. Molecules in excited states [2,3] may possess enough internal energy to overcome the activation barrier, but may still not be easy to trap. We will discuss results involving

– calculations of cross sections for inelastic and reactive processes in benchmark

– systems at ultra-low temperatures. Additional studies with model calculations

– will also be presented in order to explore the theoretical possibility of

– enhancing chemical reactivity at ultra-low energies [4].

[1] E. Bodo, A. Dalgarno, F. A. Gianturco: J. Chem. Phys. 116, 9 222 (2002) [2] E. Bodo, F. A. Gianturco, A. Dalgarno: J. Phys. B 35, 2 391 (2002) [3] E. Bodo and F. A. Gianturco: Eur. Phys. J. D 31, 423 (2004) [4] E. Bodo, F. A. Gianturco, N. Balkrishnan, A. Dalgarno: J. Phys. B 37, 1 (2004)

45

Measurement of the Electron Electric Dipole Moment using Cold Yb F Molecules

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PAUL CONDYLIS

Imperial College London, Blackett Laboratory, London SW7 2AZ/GB

The electron’s permanent electric dipole moment (EDM) is predicted by various particle theories through the interaction of the electron’s virtual particle cloud and the quantum vacuum. If the electron were found to have such a property it would constitute a gross violation of time reversal symmetry and parity. At Imperial College centre for cold matter we use a pulsed supersonic YbF beam to measure the EDM of the electron. The poster will provide detailed information about how the experiment is performed and why the use of cold molecules in the experiment is important.

46

Threshold effects in the photoassociation of cold atoms: R–6 model in the Milne formalism

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ANNE CRUBELLIER AND ELIANE LUC-KOENIG

Laboratoire Aimé Cotton, bât. 505, Campus d’Orsay, 91405 Orsay Cedex, France

Photoassociation of ultracold atoms is now investigated at very low temperature, below 50 µK, and there is a need of accurate description of the energy-dependence of the photoassociation probability. At low energy, a quantum calculation of the wavefunc-tion is necessary to describe the threshold effects. As the collision energy E = k 2 decreases towards zero, there is a characteristic internuclear range ∆ R(k) where the WKB treatment of the wavefunction fails, preventing a semiclassical connection between the R-range where photoassociation occurs and the asymptotic range where the energy normalization condition, necessary to obtain absolute value for the photoassociation rate, is imposed to the wavefunction [1].

At low energy, s-wave collisions prevail and the photoassociation probability relies on the value of the density probability |Ψ(Rc , k)|2 of the s-wavefunction in the ground state potential at the Condon radius Rc; the internuclear distances are such as the long-range behaviour –C6/R6 of the potential is reached.

The aim of the present work is to analyze the systematic trends of the variations of the probability density |Ψ(Rc , k)|2 as a function of Rc and k, for various systems charac-terized by different values of the scattering length l. We use here a simplified version of previously described singlechannel [2] and multichannel [3] asymptotic models, which consists in a R–6 potential limited at short range by a repulsive wall, with a tunable posi-tion chosen to reproduce the scattering lenght l of the studied system. The quantum Milne phase-amplitude formalism [4] is used to calculate quantum wavefunctions. Two forms connected to the WKB limit, valid respectively on both sides of the quantum threshold range ∆R(k) are presented. Analytical expressions valid in both R-domains over a large energy-range near zero energy are deduced. This analysis generalizes some recent results [5] and extends them to the description of photoassociation toward excited vibrational levels with large binding energy.

This model can be extended to the analysis of near-threshold behaviours in quantum systems described by an asymptotic potential 1/R n with n > 2 . In particular it allows the definition of a generalized scattering length for the 1/R 3 potential.

[1] P. S. Julienne: J. Res. Natl. Inst. Stand. Technol. 101, 487 (1996) [2] A. Crubellier, O. Dulieu, F. Masnou-Seeuws, M. Elbs, H. Knöckel, E. Tiemann:

Eur. Phys. J. D 6, 211 (1999) [3] N. Vanhaecke, Ch. Lisdat, B. T’Jampens, D. Comparat, A. Crubellier, P. Pillet:

Eur. Phys. J. D 28, 351 (2004) [4] W. E. Milne: Phys. Rev. 35, 863 (1930) [5] C. Boisseau, E. Audouard, J. Vigué, P. S. Julienne: Phys. Rev. A 62, 052 705 (2000)

47

Decelerating heavy polar molecules T

ue

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R. V. DARNLEY, M. R. TARBUTT, J. J. HUDSON, B. E. SAUER, E. A. HINDS

Centre for Cold Matter, Department of Physics, Imperial College London, SW7 2BW

A measurement of the electron’s electric dipole moment (edm) provides an excellent probe of theories that extend the standard model of particle physics, such as super-symmetry. Certain heavy polar molecules offer exceptional sensitivity to the electron’s edm. At Imperial College, we are measuring the edm using high resolution molecular-beam spectroscopy techniques [1]. Cold, trapped molecules offer the prospect of long interrogation times leading to greatly-enhanced sensitivity. A number of other ultra-high resolution molecular spectroscopy experiments would also benefit from cold, trapped molecules. These include the measurement of parity violation in molecules where the sensitivity to the fundamental couplings of the Z0 boson can be greatly enhanced [2], a study of the role played by the weak interaction in the emergence of homochirality [3], and measurements of the time-variation of fundamental constants [4].

We are building a Stark decelerator suitable for heavy polar molecules. The Stark deceleration principle uses a sequence of switched electric field gradients to decelerate pulses of supersonically cooled molecules. It is most easily applied to molecules in states with a positive Stark shift (weak-field seeking states), as demonstrated with great success for CO, NH3 and OH [5,6]. Deceleration becomes more difficult for heavier molecules whose kinetic energy is correspondingly larger. It becomes advantageous to use the rota-tional ground state where the Stark shift is greatest so that the number of deceleration stages required remains feasible.

Use of the strong-field seeking rotational ground state poses a serious problem – the electric fields are strongest on the surface of the decelerator’s electrodes and so the molecular beam will diverge as it is decelerated. This problem can be avoided by using an alternating sequence of positive and negative lenses, which if carefully arranged have a net focussing effect in both transverse directions. A prototype › alternating gradient ‹ Stark decelerator has already been used to demonstrate a small reduction in energy of CO molecules [7], and the heavy molecule YbF [8], both in strong-field seeking states.

Our new alternating gradient decelerator is designed to bring YbF molecules to rest using 100 stages operated at fields of 200 kV/cm. The first section, consisting of 21 stages, is now operational. We will present the design details of this decelerator and our most recent deceleration results.

[1] J. J. Hudson, B. E. Sauer, M. R. Tarbutt, E. A. Hinds: Phys. Rev. Lett. 89, 023 003 (2002) [2] D. DeMille: private communication [3] Ch. Daussy et al.: Phys. Rev. Lett. 83, 1 554 (1999) [4] J. Darling: Phys. Rev. Lett. 91, 011 301 (2003); H. L. Bethlem, private communication [5] H. L. Bethlem and G. Meijer: Int. Rev. Phys. Chem. 22, 73 (2003) [6] J. R. Bochinski, E. R. Hudson, H. J. Lewandowski, G. Meijer, J. Ye: Phys. Rev. Lett. 91, 243 001 (2003). [7] H. L. Bethlem, A. J. A. van Roij, R. T. Jongma, G. Meijer: Phys. Rev. Lett. 88, 133 003 (2002). [8] M. R. Tarbutt et al.: Phys. Rev. Lett. 92, 173 002 (2004).

48

Experimental Investigation of Ultra-Cold Collisions of Potassium

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ST. FALKE, I. SHERSTOV, E. TIEMANN, CH. LISDAT

Institut für Quantenoptik, Universität Hannover, Germany www.iqo.uni-hannover.de, falke @ iqo.uni-hannover.de

A cold collision of two atoms is strongly influenced by the long-range part of inter-action potentials for the two colliding partners. This long-range interaction can be deter-mined by molecular spectroscopy of weakly bound molecular ro-vibrational levels close to the asymptote of interest. This spectroscopy can be done by photoassociation, i.e., starting from cold atoms. There are important limitations of this method: To determine ground state scattering properties, at least two photons and hence coherent coupling effects have to be considered. Photoassociation close to the atomic resonance line is difficult due to overlapping structures and perturbations of the trap by the nearly reso-nance light. However, these levels carry a significant part of the information of the long-range interaction.

Such disadvantages can be overcome by starting molecular spectroscopy from deeply bound molecules. The well established method of molecular beams provides molecules, which allow for spectroscopy with comparable or better accuracy than in photoassocia-tion experiments. Both, electronic ground states and electronically excited states can be studied, thus the collisions of two ground state atoms or collisions of a ground state atom with an electronically excited atom can be quantitative described.

We will present our experiments on the K2 A 1Σu+ state, which is of interest not only

for the description of the 4s ← 4p collision but also as a pathway for experiments aiming on the precise description of two colliding ground state atoms. We perform a double-resonance experiment on a molecular beam. Our spectroscopic data connect to our earlier investigations [1] and experiments on thermal ensembles [2,3] on the low energy side and to photoassociation experiments on the high-energy side [4].

Our experiments prepare for two further experiments: (1) In the molecular beam there are not only 39K2 dimers but also a significant number of hetero-nuclear 39K41K dimers. These will not show a clean R–3 asymptote for the A state. (2) As indicated above, bound levels and resonances at the ground state asymptotes can be investigated via the A state. This will allow for a precise description of ultra cold K – K collisions, which are important in trap experiments.

[1] Ch. Lisdat et al.: Eur. Phys. J. D 17, 319 (2001) [2] A. Ross et al.: J. Phys. B 20, 6225 (1987), G. Jong et al.: J. Mol. Spec. 155, 115 (1992), C. Amiot et al.:

J. Chem. Phys. 103, 2 250 (1995) [3] M. R. Manaa et al.: J. Chem. Phys. 117, 11 208 (2002), T.~Bergeman: private communication [4] H. Wang et al.: Phys. Rev. A 55, R1569 (1997)

49

Creation of a Bose-Einstein condensate of molecules and strongly interacting Fermi gases

in the BEC-BCS crossover

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M. BARTENSTEIN1, A. ALTMEYER1, S. RIEDL1, R. GEURSEN1, S. JOCHIM1,C. CHIN1, J. HECKER DENSCHLAG1, R. GRIMM11 ,,22

1 Institut für Experimentalphysik, Universität Innsbruck, 6020 Innsbruck, Austria 2 Institut für Quantenoptik und Quanteninformation,

Österreichische Akademie der Wissenschaften, 6020 Innsbruck, Austria

The formation of composite bosons by pairing fermions leads to intriguing phenom-ena in physics, with superconductivity and 3He superfluidity being prominent examples. In an ultracold gas of fermionic atoms, the pairing interaction can be tuned and offers exciting possibilities to explore molecular Bose-Einstein condensation ( BEC) in the strong-coupling regime and Cooper-paired superfluidity in the weak-coupling regime.

We produce a Bose-Einstein condensate of Li2 molecules in an optical trap starting from a spin mixture of fermionic 6Li atoms [1]. To form molecules, we employ a broad Feshbach resonance located at a magnetic field of 850 G. Below the resonance, where a stable, weakly bound molecular state exists, molecules can be efficiently formed when the thermal energy is lower than the molecular binding energy. Further evaporative cooling by lowering the optical trap leads to the condensation of the molecules. The molecular BEC is remarkably stable and has a long lifetime of > 40 s near the Feshbach resonance.

Our pure molecular BEC is an ideal starting point to explore the BEC-BCS crossover. We observe a smooth conversion of the condensate to a degenerate Fermi gas by adia-batically ramping the field across the Feshbach resonance [2]. In the crossover regime, the sample is strongly interacting. Progress in the study of this system will be presented.

[1] S. Jochim et al.: Science 302, 2 101 (2003) [2] M. Bartenstein et al.: Phys. Rev. Lett. 92, 120 401 (2004)

50

Formation of stable ultracold molecules after photoassociation with chirped pulses

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CHRISTIANE P. KOCH, ELIANE LUC-KOENIG, FRANÇOISE MASNOU-SEEUWS

Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France

Photoassociation is creating ultracold molecules in an excited electronic state: in order to make stable molecules, a radiative stabilization process should be implemented to bring some of the molecules into a bound vibrational level of the ground state. Stabiliza-tion via spontaneous emission, widely used in cold gases [1], cannot be considered in condensates because of coherence loss: schemes involving induced emission should therefore be explored. Previous theoretical work [2,3] has investigated photoassociation of cesium with chirped laser pulses, showing transfer of population to several (≈15) vibrational levels v' in the external well of the 0g

– (6 s +6 p3/2 ) potential curve, forming a wavepacket. Taking advantage of the scaling laws on the vibrational periods, spreading around a central value Tvib, it is possible to choose the linear chirp parameter so that the wavepacket is shaped in order to fulfill revival [4] conditions. At time Tvib /2 after the pulse, a focussing effect is observed at the inner turning point.

The aim of the present work is to discuss how a second pulse can coherently transfer population to bound levels v" of the ground state. The initial state is the focussed wave-packet at time Tvib /2 described above and renormalized to 1 in order to obtain directly probabilities. Various short pulses are considered, with convenient central frequency, their duration being small enough to avoid spreading of the focussed wave packet in the excited state, so that the system can be analyzed as an effective two-level system. Once the spectral width is large enough to cover all levels with good Franck-Condon overlap, the parameters of the second pulse can be chosen to obtain complete population inversion. Analysis of the distribution of the transferred population over the various levels v" will be discussed at the conference.

[1] A. Fioretti, D. Comparat, A. Crubellier, O. Dulieu, F. Masnou-Seeuws, P. Pillet: Phys. Rev. Lett. 80, 4 402 (1998); A. N. Nikolov, E. E. Eyler, X. Wang, J. Li, H. Wang, W. C. Stwalley, P. Gould: Phys. Rev. Lett. 82, 703 (1999); C. Gabbanini, A. Fioretti, A. Lucchesini, S. Gozzini, M. Mazzoni: Phys. Rev. Lett. 84, 2 814 (2000)

[2] E. Luc-Koenig, R. Kosloff, F. Masnou-Seeuws, M. Vatasescu: Phys. Rev. A 70, 033 414 (2004) [3] E. Luc-Koenig, M. Vatasescu, F. Masnou-Seeuws: Eur. Phys. J. D 31, 239 (2004) [4] I. Sh. Averbukh and N. F. Perelman: Phys. Lett. A 139, 449 (1989)

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Analysis of the multiphoton ionization of cold rubidium dimers

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J. LOZEILLE1, A. FIORETTI1, O. DULIEU2, C. GABBANINI1

1 IPCF-CNR, Via G. Moruzzi 1, 56124 Pisa, Italy

2 Laboratoire Aimé Cotton, CNRS, Campus d’Orsay, 91405 Orsay Cedex, France

In previous studies [1,2] translationally cold (~90 µK) Rb2 molecules, produced in a magneto-optical trap in their triplet ground state through photoassociation and radiative decay, have been detected by two-photon ionization and selective mass spectroscopy in order to record the Rb2

+ ions. The ionization process is resonantly enhanced by the intermediate a 3Σu

+ → (2) 3Πg molecular band. The (2) 3Πg state is correlated with the 5 S + 4 D asymptote.

Here an analysis of the ionization spectra is performed by a simulation of the full process, starting from the photoassociation of colliding atom pairs. A quantitative approach for the states correlated with the 5 S + 4 D asymptote is considered by intro-ducing the spin-orbit interaction as a perturbation, as similarly performed for the S + P case[2,3].

[1] C. Gabbanini et al: Phys. Rev. Lett. 84, 2 814 (2000) [2] A. Fioretti et al.: Eur. Phys. J. D 15, 189 (2001) [3] A. Fioretti et al.: Eur. Phys. J. D 5, 389 (1999)

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Sympathetic Cooling of Complex Molecular Ions: Progress report

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ALEXANDER OSTENDORF, BERNHARD ROTH, CHAOBO ZHANG, STEPHAN SCHILLER

Heinrich-Heine-Universität Düsseldorf

Ultracold molecular ions embedded inside Coulomb crystals are very promising for a variety of studies in molecular physics, quantum optics and fundamental physics.

We have developed a versatile experimental setup suitable for sympathetic cooling of molecular ions covering the wide mass range from 20 up to 20 000 amu. As coolant we use lasercooled 138Ba+-ions in a linear rf-trap. So far we have produced lasercooled barium ion crystals of different sizes and shapes by varying trapping parameters and the amount of barium. We also succeeded in embedding Ar+ and CO2

+ in the ion crystals corresponding to a mass ratio of mBa /mSympCooled = 3.45 which to our knowledge is the largest value achieved so far.

We will also report on the extension of the apparatus to cool heavy multiply charged molecules generated by electrospray ionization and transferred to the experimentation chamber.

53

Atom Entanglement by Kapitza-Dirac Superradiance

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K. M. R. VAN DER STAM, E. D. VAN OOIJEN, J. M. VOGELS, P. VAN DER STRATEN

Debye Institute, Department of Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80 000, 3508 TA Utrecht, The Netherlands

Recently, our group achieved Bose-Einstein condensation of sodium. A thermal atomic beam is slowed longitudinally by means of a Zeeman slower after which the diver-gence of the beam is compensated by means of a Magneto-optical lens. Subsequently, a dark-spot MOT is loaded from this beam, resulting in roughly 1010 trapped atoms with a density of 3 ⋅ 1011 cm–3. Next, the MOT is transferred to a magnetic trap in the clover leaf configuration to provide us with full 360o optical access. After applying evaporative cooling we are able to produce a BEC containing roughly 50 ⋅ 106 atoms at a Tc = 150 nK.

Currently we are investigating the coherent properties of the condensate by measuring the superradiance emission. We illuminate the BEC with a single laser pulse. The atoms that are scattered by the laser beam will interfere with the atoms at rest and create a density modulation. The diffraction of the laser beam from this grating leads to super-radiance. The emission of the photons is the strongest along the long axis of the condensate, called endfire beam. This in combination with the pump beam gives the atoms a recoil at an angle of 45 degree with respect to the incoming beam.

A second process, where an atom absorbs a photon from the endfire beam, and sub-sequently emits it in the original laser beam, is also possible in the regime of short laser pulses in which several recoil states are degenerate. This off-resonant process is called Kapitza-Dirac superradiance. At the moment we are trying to make this process more efficient by applying a second laser pulse with a small frequency difference in order to drive the second process resonantly. This should make it possible to increase the number of atoms in the Kapitza-Dirac state.

Fig. 1: The scattering process for a 10 µs laser pulse. The two circles on the left are the atoms coupled out of the condensate by superradiance. The two on the right are formed by Kapitza-Dirac diffraction.

References:1) D. Schneble, Y. Torii, M. Boyd, E. W. Streed,

D. E. Pritchard, W. Ketterle: The Onset of Matter-Wave Amplification in a Superradiant Bose-Einstein Condensate, Science 300, 475.

54

Building an atom laser, the subsonic way

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J. M. VOGELS, P. VAN DER STRATEN

Debye Institute, Department of Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80 000, 3508 TA Utrecht, The Netherlands

We are developing an atom laser by cooling a thermal, subsonic atom beam along its path towards degeneracy. We will exploit a shock wave to force the atoms from a super-sonic flow to a subsonic flow, after which the beam is compressed before evaporative cooling is started. By exploiting the properties of the subsonic beam we are able to reach degeneracy in a compact setup. The expected flux of this subsonic atom laser (108 atoms per second) supersedes that of the current state-of-the-art experiments in Bose-Einstein condensation by two orders of magnitude. We propose to use the beam properties of a subsonic laser atom for novel experiments in Bose-Einstein condensation, such as the study of radiation emitted from an event horizon and parametric down conversion. The atom laser proposed here would be particularly versatile and can be used as a source for many experiments in the field of quantum gases.

55

Wednesday 22 February 2005

Morning session

(9.00 – 12.30)

Chair: Ronnie Kosloff

09.00 – 09.45 Pepijn W. H. Pinkse – 58

09.45 – 10.30 Hendrick L. Bethlem – 59

10.30 – 11.00 Coffee

11.00 – 11.45 Jean-Michel Launay – 60

11.45 – 12.30 Franco Gianturco – 61

57

Trapping slow dipolar molecules in three and two dimensions using

static and switching electric fields

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P. W. H. PINKSE, T. RIEGER, T. JUNGLEN, S. A. RANGWALA, G. REMPE

Max - Planck - Institut für Quantenoptik, Hans - Kopfermannstr. 1, D - 85748 München, Germany

Success in the field of cold molecules depends on the ability to make beams of slow molecules, cool and trap these. We have demonstrated a novel method to create a slow molecular beam from an effusive source [1]. Molecules from a room-temperature effusive source are injected into a bent electrostatic quadrupole guide, which acts as a velocity filter for molecules in low-field-seeking Stark states. An effective temperature of the guided molecules (ND3 or H2CO) around 1 K is attained for reasonable experimental parameters. These molecules are transported into another chamber, where they can be handled in an ultrahigh vacuum. Here, we have successfully built a large volume electrostatic trap that is filled continuously from the guide. Molecules with velocities smaller than about 20 m /s are trapped with motional temperatures below 0.5 K.

Subsequent cooling of the trapped molecules poses new challenges. As optical methods are unwieldy due to the large number of molecular states that can be populated, evaporative or sympathetic cooling using collisions form an attractive alternative. However, at higher densities, inelastic state-changing collisions could be an important loss channel of molecules, if only low-field seekers are trapped. Thus the need to manipulate both low- and high-field seekers simultaneously is vital. This can be attained in the present experimental setup by using switching electric fields in the place of static fields for our quadrupolar guide. An analytic analysis of the harmonic part of the potential reveals simultaneous, stable trapping conditions. A more realistic numerical analysis shows rich behaviour caused by anharmonic parts by the potential. A two-dimensional trapping potential of the order of 10 mK can be obtained for low-field-seeking states, slightly less for highfield-seeking states. We have experimentally demonstrated electrodynamic trapping and guiding of slow ND3 molecules in the four-rod guide operated with an alternating electric dipole potential [2]. We find good agreement with the numerical results.

[1] S. A. Rangwala, T. Junglen, T. Rieger, P. W. H. Pinkse, G. Rempe: Phys. Rev. A 67, 043406 (2003); T. Junglen, T. Rieger, S. A. Rangwala, P. W. H. Pinkse, G. Rempe: Eur. Phys. J. D 31, 365 (2004).

[2] T. Junglen, T. Rieger, S. A. Rangwala, P. W. H. Pinkse, G. Rempe: Phys. Rev. Lett. 92, 223 001 (2004)

58

Deceleration and trapping of polar molecules in high-field-seeking states

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HENDRICK L. BETHLEM

Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4 – 6, 4195 Berlin, Germany

FOM-Institute for Plasmaphysics » Rijnhuizen « , Edisonbaan 14, 3439 MN Nieuwegein, the Netherlands.

Neutral polar molecules can be decelerated and trapped using time-varying inhomo-geneous electric fields. This has been succesfully applied to molecules in low-field-seeking states. We aim to extend this method to molecules in high-field-seeking states for two reasons; (i) heavy molecules such as YbF and bio-molecules have no suitable low-field-seeking states, and (ii) the ratio of elastic to inelastic cross section of polar molecules in low-field-seeking states is predicted to be insufficient to permit evaporative cooling. I will present results on the deceleration of CO and YbF using an Alternate Gradient decelerator and on trapping para-ammonia molecules in their absolute ground-state using an electrodynamic trap.

59

Quantum dynamics of alkali atom – alkali dimer collisions involving three identical

spin-stretched atoms

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J.-M. LAUNAY, P. HONVAULT, G. QUEMENER

PALMS, UMR 6627 du CNRS and Université de Rennes 1, France

M. T. CVITAŠ, D. E. POTTER, P. SOLDÁN, J. M. HUTSON

Department of Chemistry, University of Durham, England

Alkali dimers of fermionic atoms such as 6Li2 and 40K2 have recently been condensed in several groups. Collisional processes have an important role in the formation and decay of Bose-Einstein condensates and there is currently a growing interest in the theo-retical determination of elastic and quenching collision rate coefficients at ultracold temperatures. Using ab initio potential energy surfaces and a quantum-mechanical scat-tering formalism based on hyperspherical democratic coordinates, we have studied the dynamics of several atom – dimer systems which involve three identical spin-stretched bosonic or fermionic alkalis.

We have obtained fully converged cross sections for the 6Li + 6Li2 and 7Li + 7Li2 systems in the energy range 1 nK – 500 mK [1]. For both the bosonic and fermionic species the total quenching rate coefficient of the lowest rotational state of the v = 1 rovibrational manifold can be obtained semi-quantitatively by a Langevin capture model for energies larger than 10 mK. At lower energies Wigner threshold laws apply, the total quenching rate is larger than the elastic one by several orders of magnitude and is not suppressed for fermionic atoms.

Converged rate coefficients for the lowest (v = 1, j ) rovibrational state have been obtained for the three species 39K, 40K and 41K [2]. We have analysed the differences between these systems and found that the transition between the Wigner and Langevin regimes lies around 100 µK. The quenching rate coefficient is larger than the elastic one for energies less than 1 mK for all systems.

We also performed a systematic study of the sensitivity of elastic and quenching rate coefficients to the non additive part of the interaction potential in Na + Na2 collisions at ultralow energies [3]. The v = 1 rate coefficients are more sensitive than the v = 2 and v = 3 ones while the ratios quenching /elastic are less sensitive than the rate themselves. However rotational distributions in all final vibrational states v' are very sensitive. Finally, we will describe preliminary results obtained at ultralow energies for vibrational states of Li2 close to the dissociation limit.

[1] M. T. Cvitaš, P. Soldán, J. M. Hutson, P. Honvault, J.-M. Launay: http:// www.arxiv.org/cond-mat/0409 709, Phys. Rev. Lett., in press (2005)

[2] G. Quéméner, P. Honvault, J.-M. Launay, P. Soldán, D. E. Potter, J. M. Hutson: http:// www.arxiv.org/cond-mat/0411 158, Phys. Rev. A, in press (2005)

[3] G. Quéméner, P. Honvault, J.-M. Launay: Eur. Phys. J. D 30, 201 (2004)

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Ultracold Chemistry: Interaction Forces and Energy Transfers in

Reactive and Quenching Collisions

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Department of Chemistry, The University of Rome » La Sapienza « , Piazzale A. Moro 5, 00185 Rome, Italy

The last few years have witnessed a tremendous upsurge of interest in the study of molecular systems under very cold conditions, where by » cold « one usually designates molecules that have translational temperatures between 1 and 1 000 µK, while » ultracold « molecular matter involves translational temperatures which are typically less than 1 µK and where the particle dynamics is dominated by single partialwave contributions to scattering events.

The theoretical interest on the many, novel findings of the experiments has also un-dergone a rapid increase and several research groups have begun to study the behaviour of fairly » familiar « processes occurring at room temperatures down to much lower tem-peratures and relative collision energies.

In the present talk I shall endeavour to describe the work done in our group in Rome on the analysis of the quantum dynamics involved in describing collisional de-excitation (cooling) of rotational and vibrational degrees of freedom in simple molecules by inter-acting with one of the most popular buffer gas, the one made of 4He and /or 3He atoms. I will also discuss the surprising new features involving gas-phase chemical reactions once theoretical work is carried out at very low collision energies, where special enhancement effects are discovered in simple systems by accurate calculations. References:

1) E. Bodo, F. A. Gianturco, A. Dalgarno:

F + D2 reaction at ultra-cold temperatures, J. Chem. Phys. 116, 369 222 (2002)

2) E. Bodo, F. A. Gianturco, A. Dalgarno: The reaction of F + D2 at ultracold temperatures: the effect of rotational excitation, J. Phys. B 35, 4 075 (2002)

3) E. Bodo, F. Sebastianelli, E. Scifoni, F. A. Gianturco, A. Dalgarno: Rotational qenching of ionic systems at ultracold temperatures, Phys. Rev. Lett. 89, 283 201 (2002)

4) E. Bodo, and F. A. Gianturco: Collisional Cooling of polar diatomics in 3He and 4He buffer gas: a quantum calculation at ultra-low energies, J. Phys. Chem. A 107, 7 328 (2003)

5) E. Bodo, F. A. Gianturco, F. Sebastianelli, E. Yurtsever, M. Yurtsever: Collisional cooling of Li2 (1Σu+) by » ultracold « collisions with an 4He buffer gas, Theor. Chem. Acc. 112, 263 (2004)

6) E. Bodo, F. A. Gianturco, N. Balakrishnan, A. Dalgarno: Chemical reactions in the limit of zero kinetic energy: virtual states and Ramsauer minima in F + H2 → F + H, J. Phys. B 37, 3 641 (2004)

7) E. Bodo and F. A. Gianturco: Features of chemical reactions at vanishing collision energies: The role of internally » hot « molecular partners, Eur. Phys. J. D 31, 423 (2004)

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Wednesday 22 February 2005

Contributed talks

(14.00 – 15.30)

Chair: Olivier Dulieu

14.00 – 14.15 Johann Nagl – 64

14.15 – 14.30 Wolfgang Ernst – 65

14.30 – 14.45 Matthias Weidemüller – 66

14.45 – 15.00 Joost M. Bakker – 67

15.00 – 15.30 Jun Ye – 68

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Spectroscopy of Rb2 and K Rb on He nanodroplets

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J. NAGL, G. AUBÖCK, C. CALLEGARI, W. E. ERNST, L. WINDHOLZ

Institut for Experimental Physics, Technical University of Graz Petersgasse 16, A - 8010 Graz

Helium droplets formed in a supersonic expansion are presently a valid complement to photoassociation for the production and spectroscopic investigation of cold molecules.

Expansion of high-pressure gas (up to 100 bar) from a low temperature source (~10 K ) yields droplets of average size N = 104 He atoms. Evaporative cooling regulates the internal temperature of the droplet (~0.4 K ).

The droplets pass through a pick-up cell containing alkali gas at low pressure, where each droplet is loaded with a statistical number of alkali atoms. The atoms remain on the surface of the droplet, where they move freely and form bound complexes upon close-distance approach. Because the binding energy is dissipated into the He droplet causing further evaporation and possibly destruction of the droplet, weakly bound molecules are preferentially formed: in our case alkali dimers in their lowest high spin (triplet) state.

The measured electronic absorption spectra are only weakly perturbed by the droplets (the main effect being a modest broadening ) and can normally be assigned from the simulated spectra of the free species. Because the presence of the droplet does not quench the fluorescence from the excited molecules, emission spectra are also easily measured; in most cases emission occurs form free molecules which have come to separate form the droplet upon excitation.

We have investigated the electronic absorption and emission spectra of Rb2 and K Rb formed in their lowest triplet state on the surface of He droplets. The results of the measurements, along with the calculated spectra, will be presented.

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Cesium dimer spectroscopy on helium droplets

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W. E. ERNST, R. HUBER∗, S. JIANG‡,

Institut für Experimentalphysik der technischen Universitate Graz, Petersgasse 16, A - 8010 Graz, Austria

R. BEUC, M. MOVRE, G. PICHLER

Institute of Physics, Bijenička cesta 46, HR -10000 Zagreb, Croatia

Visible absorption spectra of cesium dimer on helium nanodroplets between 14 500 cm–1 and 17 600 cm–1 were probed by laser induced fluorescence. A strong absorption band peaking around 16 700 cm–1 is identified as Cs2 1(a) 3Σu

+ – 3 3Σg+ transition. A broad un-

structured band near 17 520 cm–1 is interpreted as Cs2 1( X ) 1Σg+ – 2 1Σu

+ transition. The assignments are discussed on the basis of ab initio potential curves calculated by

Meyer and Spies. All spectra have been modeled using a narrow Frank-Condon window connected with the equilibrium distance in the ground singlet and triplet states. Many observed absorption peaks of smaller intensities could be identified, although some of them violet transition rules for the cesium dimers. We discuss the possible origin of the corresponding transitions.

∗ present address: University of Delaware, USA ‡ present address: Tsinghua University, PRC

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Formation of cold bialkali molecules on Helium nanodroplets

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MATTHIAS WEIDEMÜLLER1, MARCEL MUDRICH1,2, OLIVIER DULIEU2, OLIVER BÜNERMANN3, FRANK STIENKEMEIER3

1 Institute of Physics, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany 2 Laboratoire Aimé Cotton, 91405 Orsay Cedex, France

3 Faculty of Physics, Universität Bielefeld, 33615 Bielefeld, Germany

Superfluid helium nanodroplets are doped with combinations of different alkali atoms ( Li, Na, Rb, Cs). The atoms form molecules on the surface of the droplets which thermalize at the droplet temperature ( T < 0.4 K ) [1]. Different detection schemes (photoionization, laser-induced fluorescence and laser-induced beam depletion) are employed to reveal detailed information on the binding and the internal states of the molecules. Besides the formation of heteronuclear alkali dimers ( LiCs, NaCs) we observe Cs He* exciplexes at excitation frequencies close to the cesium D1 and D2 transitions. Characteristic features in the cesium excitation spectrum are identified as Cs3 trimer states.

Excitation spectra of the heteronuclear alkali dimers in the frequency range of a tunable Ti:Sa-laser are recorded. The observed vibrational progressions are identified in terms of transitions within the triplet ground-state manifold. Ab initio potential curves from literature are extended to include the influence of atomic fine-structure. Compari-son with the observed spectra yields improved potentials. Laser-induced desorption of the heteronuclear dimers is observed which opens perspectives to create a beam of free, cold heteronuclear molecules for precision spectroscopy or to provide a source for deceleration and trapping of polar molecules.

[1] F. Stienkemeier, W. E. Ernst, J. Higgins, G. Scoles: Phys. Rev. Lett. 74, 3 592 (1995)

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Towards Magnetic Trapping of Ultracold Polar Molecules

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JOOST M. BAKKER

Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4 – 6, 4195 Berlin, Germany

Buffer gas loading and subsequent magnetic trapping of neutral molecules is a powerful tool for the creation of dense samples of ultracold molecules and is applicable to a wide variety of paramagnetic species. Such dense samples of ultracold molecules can form a starting point for experiments aimed at studying the formation of a molecular quantum gas, to perform ultra-high resolution spectroscopic measurements, and to test fundamental physics or interactions between ultracold molecules. In this project we aim to create dense samples of neutral paramagnetic molecules by means of buffer-gas loading and trapping inside a superconducting quadrupole magnet using a 3He – 4He dilution refrigerator.

We report on the progress of the experiments using atomic Chromium. We also discuss the perspectives for cooling and trapping OH and NH radicals.

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Cold polar molecules – Stark deceleration, precision spectroscopy, and future laser cooling

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JUN YE

JILA, National Institute of Standards and Technology and University of Colorado Boulder, Colorado 80309-0440, USA

We recently demonstrated the feasibility of the Stark-deceleration approach for free radicals OH. After supersonically cooled for both the internal and external degrees of freedom, ground-state OH molecules have been bunched in phase space, accelerated, slowed, and trapped using time-varying inhomogeneous electric fields to effect control via the molecules’ Stark energy shifts. In situ observation of laser-induced fluorescence along the beam propagation path allows detailed characterization of longitudinal phase-space manipulation of OH molecules. Specifically, our work from both experiment and model has been used to uncover the complex dynamics governing the evolution of the molecules within the decelerator. In our current experiment we accelerate/decelerate a supersonic beam of OH to a mean speed adjustable between 550 m/s to rest, with a translational temperature tunable from 1 mK to 1 K, corresponding to a longitudinal velocity spread from 2 to 80 m/s around a mean laboratory velocity. These velocity-manipulated stable »bunches« contain 104 to 106 molecules (depending on the tempera-ture) at a density of ~105 to 107 cm–3 in the beam and ~106 cm–3 in the trap.

In our recent experiment of precision microwave spectroscopy of the ground state structure of OH, the high detection sensitivity has allowed us to achieve a tenfold improvement in precision in determination of the Lambda-doublet and hyperfine splittings, paving the way for an enhanced test on the possible time-dependent changes in the fine structure constant, α.

To achieve a significant improvement in the phase space density of cold, ground-state, polar molecules, we are exploring laser cooling of these cold samples of molecules. The specific idea is based on enhanced scattering via a high finesse optical cavity in the 300 nm region for cavity-assisted laser cooling. The cold hydroxyl radical OH molecules will be loaded into a magnetic trap after emerging from the Stark decelerator. We expect to lower the OH temperature from 15 mK to 100 µK and below. The low-temperature and high phase-space density cold molecular sample will enable a new class of studies on collisions. For example, our group has recently performed collision experiments between an ultracold sample of Rb atoms and OH molecules, with the goal to understand the collision process between reactive atoms and molecules in a cold temperature environ-ment and to eventually realize sympathetic cooling of molecular species via ultracold atoms. Currently such collisional dynamics have not been measured definitively due to the low density limit of the cold OH molecules. We are also interested in the properties of elastic vs. inelastic collisions among the cold polar molecules under various electro-magnetic field configurations. An experiment that will be undertaken is to study the Hydrogen abstraction channel in the reaction between OH and formaldehyde (H2CO) under the presence of a controlled electric field and with an exquisite control of the collision energy resolution.

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Wednesday 22 February 2005

Hot Topics

(16.30 – 17.00)

Chair: Olivier Dulieu

16.30 – 16.45 Ronnie Kosloff – 70

16.15 – 17.00 Pierre Pillet – 71

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Making cold molecules with cold atoms and chirped laser pulses

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E. LUC-KOENIG1, M. VATASESCU1,2, R. KOSLOFF3, F. MASNOU-SEEUWS1

1 Aimé Cotton, bât 505, Campus d’Orsay, 91405 Orsay Cedex, France 2 Institute of Space Sciences, MG-23, 76911 Bucharest Magurele, Roumanie,

3 Department of Physical Chemistry, The Hebrew University, Jerusalem 91904, Israel.

One route to ultracold molecules is the photoassociation reaction [1]. As an example, we have considered the reaction involving ultracold cesium atoms at 50 µK:

Cs (6s 2S1/2 ) + Cs (6s 2S1/2 ) + h(ν0 – δ) → Cs2 (0g– (6s 2S1/2 + 6p 2P3/2 ); v, J = 0

which has been widely studied in experiments using cw lasers [2], at a frequency red-detuned by δ relative to the atomic line ν0. At resonance, only one vibrational level is populated in the external well of the 0g–

double well potential. The short-lived molecules can further be stabi-lized by spontaneous emission to a bound level of the ground triplet state [2].

In the present work, we discuss the efficiency of excitation with chirped laser pulses, considering a time-dependent instantaneous frequency ν(t ) = ν0 – δ(t ). Numerical calculations are performed, where the initial state is described by a stationary continuum wavefunction of the ground triplet state, represented with a recently developed mapped sine grid method [3]. The time-dependent Schrödinger equation is solved through expansion in Chebychev poly-nomia [4]. In the example chosen, an important population transfer is achieved to ≈15 vibrational levels, around the resonant level, in the energy range swept by h ν(t ) [5]. Levels outside this » photoassociation window « may be significantly populated during the pulse, but no population remains after it. Considering a reasonable repetition rate for the pulsed laser, we find that the number of molecules which are formed in the excited state is substantially larger than with a cw laser. Moreover, the population transfer to bound vibrational levels of the ground triplet state is significant, creating stable molecules with only one laser.

The results are interpreted in the framework of a two-state model, within the impulsive approximation, as an adiabatic population inversion mechanism, restricted to the photo-association window. The various time scales are discussed, as well as the adiabaticity para-meter, providing a tool to optimize the chirp in view of a very large formation rate. A hole is created in the initial state collision wavefunction, in the range corresponding to the photo-association window, which may influence the pair dynamics in condensates.

Another mechanism [6] involves a non-adiabatic population transfer, at large internuclear distances, outside the photoassociation window. Levels are populated close to the disso-ciation limit, their vibrational period being comparable to the radiative lifetime. However, the wavepacket is accelerated due to a momentum » kick «, reducing the time necessary to reach the inner region where stabilization can take place.

[1] H. R. Thorsheim, J. Weiner, P. S. Julienne: Phys. Rev. Lett. 58, 2 420 (1987) [2] A. Fioretti, D. Comparat, A. Crubellier, O. Dulieu, F. Masnou-Seeuws, P. Pillet: Phys. Rev. Lett. 80, 4 402

(1998); F. Masnou-Seeuws, P. Pillet: Adv. Atomic. Mol. Opt. Phys. 42, 171 (2000) [3] K. Willner, O. Dulieu, F. Masnou-Seeuws: J. Chem. Phys. 120, 548 (2004) [4] R. Kosloff: Annu. Rev. Phys. Chem. 45, 145 (1994) [5] E. Luc-Koenig, R. Kosloff, F. Masnou-Seeuws, M. Vatasescu: Phys. Rev. A 70, 033 407 (2004) [6] E. Luc-Koenig, M. Vatasescu, F. Masnou-Seeuws: Eur. Phys. J. D 31, 239 (2004)

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At the frontier of frozen Rydberg gases and ultracold plasmas

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PIERRE PILLET

Laboratoire Aimé Cotton, CNRS, Bât. 505, Campus d’Orsay, 91405 Orsay, France contact: pierre.pillet @ lac.u-psud.fr

Dense samples of cold Rydberg atoms can evolve spontaneously to a plasma, despite the fact each atom may be bound by as much as 100 cm–1. Initially, ionization is caused by blackbody photoionization and Rydberg – Rydberg collisions. After the first electrons leave the region, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 µs caused by electron – Rydberg collisions. The resulting plasma expands slowly and persists for tens microseconds [1]. The different mechanisms involved in the whole process will be discussed [2,3]

[1] M. P. Robinson et al.: Phys. Rev. Lett. 85, 4 466 (2000) [2] Wenhui Li et al.: Phys. Rev. A 70, 042 713 (2004) [3] N. Vanhaecke et al.: accepted in Phys. Rev. A (2005), quant-ph/0401 045

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List of Participants

Olivier Allard Institut für Quantenoptik, Universität Hannover allard @ iqo.uni-hannover.de

Markus Arndt Institut für Experimentalphysik, Universität Wien markus.arndt @ univie.ac.at

Gerald Auböck Institute of Experimental Physics, TU Graz g.auboeck @ TUGraz.at

Isabelle Auffret-Babank Institute of Physics Publishing, Dirac House, Bristol iab @ iop.org

Mireille Aymar Laboratoire Aimé Cotton, Orsay mireille.aymar @ lac.u-psud.fr

Joost Bakker Fritz-Haber-Institut, Berlin jmbakker @ fhi-berlin.mpg.de

Hendrick Bethlem Fritz-Haber-Institut, Berlin rick @ fhi-berlin.mpg.de

Renat Bilyalov European Commission Square de Meus 8, B-1049 Brüssel Renat.Bilyalov @ cec.eu.int

Peter Blythe Institut für Experimentalphysik, Heinrich-Heine Universität peter.blythe @ uni-duesseldorf.de

Enrico Bodo University of Rome » La Sapienza « bodo @ caspur.it

David Carty Chemistry Research Laboratories University of Oxford david.carty @ chem.ox.ac.uk

Paul Condylis Imperial College London, Blackett Laboratory paul.condylis @ imperial.ac.uk

Anne Crubellier Laboratoire Aimé Cotton, Orsay anne.crubellier @ lac.u-psud.fr

Richard Darnley Imperial College London, Blackett Laboratory richard.darnley @ imperial.ac.uk

Michael Drewsen Department of Physics and Astronomy, University of Aarhus drewsen @ phys.au.dk

Olivier Dulieu Laboratoire Aimé Cotton Orsay olivier.dulieu @ lac.u-psud.fr

Wolfgang Ernst Graz University of Technology wolfgang.ernst @ tugraz.at

Stephan Falke Institut für Quantenoptik, Universität Hannover falke @ iqo.uni-hannover.de

Carlo Gabbanini IPCF-CNR, Pisa carlo @ ipcf.cnr.it

Reece Geursen University of Innsbruck reece.geursen @ ultracold.at

Franco A. Gianturco Department of Chemistry, University of Rome » La Sapienza « fa.gianturco @ caspur.it

Rudolf Grimm Institut für Experimentalphysik, Universität Innsbruck rudolf.grimm @ uibk.ac.at

Solvejg Jørgensen Department of Physics and Astronomy, Aarhus University solvejg @ phys.au.dk

Sebastian Jung Institut für Quantenoptik, Universität Hannover jung @ iqo.uni-hannover.de

Horst Knöckel Institut für Quantenoptik, Universität Hannover knoeckel @ iqo.uni-hannover.de

Christiane Koch Laboratoire Aimé Cotton, Orsay christiane.koch @ lac.u-psud.fr

Ronnie Kosloff Department of Physical Chemistry, Hebrew University ronnie @ fh.huji.ac.il

Tobias Kraemer Institut für Experimentalphysik, Universität Innsbruck tobias.kraemer @ uibk.ac.at

Christian Lisdat Institut für Quantenoptik, Universität Hannover lisdat @ iqo.uni-hannover.de

Jean-Michel Launay Université de Rennes 1, France jean-michel.launay @ univ-rennes1.fr

Jérémie Léonard Universiteit van Amsterdam, jleonard @ science.uva.nl

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Jérôme Lozeille IPCF-CNR, Pisa j_lozeille @ yahoo.fr

Eliane Luc-Koenig Laboratoire Aimé Cotton, Orsay eliane.luc @ lac.u-psud.fr

Françoise Masnou-Seeuws Laboratoire Aimé Cotton, Orsay francoise.masnou @ lac.u-psud.fr

Gerard Meijer Fritz-Haber-Institut, Berlin meijer @ fhi-berlin.mpg.de

Marcel Mudrich Laboratoire Aimé Cotton, Orsay marcel.mudrich @ lac.u-psud.fr

Torben Mueller Imperial College London, Blackett Laboratory mueller-torben @ web.de

Johann Nagl TU Graz, Institute of Experimental Physics j.nagl @ tugraz.at

Driss Nehari Debye Institute, Utrecht University d.nehari @ phys.uu.nl

Goran Pichler Institute of Physics, Zagreb pichler @ ifs.hr

Pierre Pillet Laboratoire Aimé Cotton, Orsay pierre.pillet @ lac.u-psud.fr

Pepijn Pinkse Max - Planck - Institut für Quantenoptik, München Pepijn.Pinkse @ mpq.mpg.de

Bernhard Roth Universität Düsseldorf bernhard.roth @ uni- duesseldorf.de

Ben Sauer Imperial College London, Blackett Laboratory ben.sauer @ imperial.ac.uk

Stephan Schiller Universität Düsseldorf step.schiller @ uni-duesseldorf.de

Peter Schmelcher Theoretische Chemie, Universität Heidelberg peter @ tc.pci.uni-heidelberg.de

Peter Staanum Physikalisches Institut, Universität Freiburg peter.staanum @ physik.uni-freiburg.de

Michael Stoll Fritz-Haber-Institut, Berlin stoll @ fhi-berlin.mpg.de

William Stwalley Department of Physics, University of Connecticut w.stwalley @ uconn.edu

Michael Tarbutt Imperial College London, Blackett Laboratory m.tarbutt @ imperial.ac.uk

Eberhard Tiemann Institut für Quantenoptik, Universität Hannover tiemann @ iqo.uni-hannover.de

Richard van der Stam Utrecht University stam @ phys.uu.nl

Peter van der Straten Utrecht University p.vanderstraten @ phys.uu.nl

Erik van Ooijen Utrecht University ooijen @ phys.uu.nl

Nicolas Vanhaecke Fritz-Haber-Institut, Berlin vanhaeck @ fhi-berlin.mpg.de

Johnny Vogels Universität Utrecht j.m.vogels @ phys.uu.nl

Matthias Weidemüller Physikalisches Institut, Universität Freiburg m.weidemueller @ physik.uni-freiburg.de

Roland Wester Physikalisches Institut, Universität Freiburg roland.wester @ physik.uni-freiburg.de

Jun Ye JILA, National Institute of Standards and Technology and University of Colorado, Boulder Ye @ jila.colorado.edu

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