ground-state physics of light-matter systems in the ultra ......when no electrons are inside the...
TRANSCRIPT
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Franco Nori
Ground-State Physics of light-matter systems
in the ultra-strong coupling regime
In collaboration with:
M. Cirio, N. Lambert, N. Shammah(RIKEN)
S. De Liberato(Southampton)
K. Debnath(EPFL)
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I would like to
thank the organizers for
their kind invitation
(this is a Haiku)
Haikus are very short Japanese poems often with 5-7-5 syllables.
Another example:
PDFs of our papersare available 24/7
in our web site
(once I gave an entire talk using Haikus)
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Brief Introduction to Cavity Quantum Electrodynamics
Ground-State Physics of light-matter systems in the ultra-strong coupling regime
Summary
Ground State ElectroluminescencePhys. Rev. Lett. 116, 113601 (2016)
Phys. Rev. Lett. 119, 053601 (2017)
Opto-mechanical transduction of virtual radiation pressure
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Ground-State Physics of light-matter systems in the ultra-strong coupling regime
Recent results (2018)
Many-Body Ground State Electroluminescence
arXiv:1811.08682 [pdf, other]Authors: Mauro Cirio, Nathan Shammah, Neill Lambert, Simone De Liberato, Franco NoriComments: 27 pages (9+19), 8 figures (3+5)
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Pedagogical review published January 2019:
A.F. Kockum, A. Miranowicz, S.D. Liberato, S. Savasta, F. Nori,
Ultrastrong coupling between light and matter
Nature Reviews Physics 1, pp. 19–40 (2019).
Free Open Access for one year (for the first issue only).
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Cavity Quantum Electrodynamics
Cavity Quantum Electrodynamics studies the interaction between matter(here represented by an atom) and the electromagnetic field confined in a cavity.
If the dimension of the atom is small compared to the wavelength of the light, we can model the light-matter coupling as a dipole interaction.
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Cavity Quantum Electrodynamics
Dipole moment of the atom Electric field at the position of the atomFree Hamiltonian
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Cavity Quantum Electrodynamics
If we consider only one electromagnetic mode inside the cavity and if we model the atom as a two level system, then the Physics is described the Rabi Hamiltonian.
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The Physics depends on three energy scales: the bare energy of the light and the atom (hereon resonance), the dipole interaction energy (Rabi Frequency) and the Energy losses .The interplay between these energy scales gives rise to different physical regimes.
Cavity Quantum Electrodynamics
Energy Loss
Bare Energy
Interaction Energy
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
Purcell Effect
E. M. Purcell et al., Phys. Rev. 69, 37 (1946)
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
Purcell Effect Rabi oscillations
E. M. Purcell et al., Phys. Rev. 69, 37 (1946)
S. Haroche group
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
Purcell Effect Rabi oscillationsVirtual photons
dressing the Ground state
Nature 458, (2009)
Nat. Phys. 6 (2010)S. Haroche group
E. M. Purcell et al., Phys. Rev. 69, 37 (1946)
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
Purcell Effect Rabi oscillations Entangled Ground State
Nat. Phys. 13, 44 (2017)S. Haroche group
Nature 458, (2009)
Nat. Phys. 6 (2010)
Virtual photonsdressing the Ground state
E. M. Purcell et al., Phys. Rev. 69, 37 (1946)
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Cavity Quantum Electrodynamics
Weak Strong Ultra-Strong Deep
Purcell Effect Rabi oscillations Entangled Ground State
Nat. Phys. 13, 44 (2017)S. Haroche group
Nature 458, (2009)
Nat. Phys. 6 (2010)
Virtual photonsdressing the Ground state
E. M. Purcell et al., Phys. Rev. 69, 37 (1946)
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Cavity Quantum Electrodynamics
G. Günter et al., Nature 458, (2009) T. Niemczyk et al., Nat. Phys. 6 (2010)
• Rydberg atoms: high dipole moments• Good Mirrors: low decay rate
Electron gas: collective enhancement
• 1-dimensional resonators: small Volume• Large Effective dipole (Capacitive coupling)
S. Haroche, J.-M. Raimond, Exploring the quantum (2006)
There are different strategies to reach strong/ultrastrong coupling
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We studied effects arising when the light-matter coupling is ultra-strong.
More specifically, we studied effects related to the dressed structure of the light-matter ground state in the ultra-strong coupling regime.
Before proceeding, let us then introduce the properties of the light-matter ground state.
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Light-Matter Ground StateIn the ultra-strong coupling regime
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Let us go back studying the Rabi Hamiltonian.
Light-matter dressed states
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Light-matter dressed states
Let us temporarily set the Rabi frequency to zero, i.e., no interaction.Now, the atom and light are independent.
The field canhave photons
The atom can be in the ground |g> or excited state |e>
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Light-matter dressed states: Let us now consider the interaction between light and matter. When it is possible to neglect the so-called counter-rotating terms,obtaining the Jaynes Cummings Hamiltonian. Now, excited states hybridize.
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In this regime the ground state is a coherent superpositionof states with different number of bare excitations.
Light-matter dressed states: In the ultra-strong coupling regime we must consider the full Hamiltonian
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Light-matter dressed states: In the ultra-strong coupling regime the expected number ofphotons in the ground state is non-zero! These are called virtual photons since they cannotbe spontaneously emitted (because the ground state has the lowest energy).
Virtual photons
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Observing virtual photons: Non-adiabatic modulation of the coupling
How to force virtual photons to be emitted?We proposed a non-adiabatic modulation of the Rabi frequency (light-matter coupling).
In collaboration with Chalmers: PRL (2009); PRA (2010); RMP (2012); PRA (2013). Experiments in Nature (2011). Top five breakthrough of 2011, according to Physics World.
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Observing virtual photons: Non-adiabatic modulation of the coupling
How to force virtual photons to be emitted?For the Dynamical Casimir Effect,we proposed a non-adiabatic modulationof the Rabi frequency (light-matter coupling).
In collaboration with Chalmers: PRL (2009); PRA (2010); RMP (2012); PRA (2013). Experiments in Nature (2011). Top five breakthrough of 2011, according to Physics World.
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Observing virtual photons: Non-adiabatic modulation of the coupling
How to force the virtual photons to be emitted?For the DCE, we proposed a non-adiabatic modulationof the Rabi frequency (light-matter coupling).
In this (more recent) work we studiedhow virtual photons in the ground state can be emitteddue to the non-adiabatic modulation of the couplinginduced by the flow of an electric current.
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Brief Introduction to Cavity Quantum Electrodynamics
Ground-State Physics of light-matter systems in the ultra-strong coupling regime
Summary
Ground State ElectroluminescencePhys. Rev. Lett. 116, 113601 (2016)
Phys. Rev. Lett. 119, 053601 (2017)
Opto-mechanical transduction of virtual radiation pressure
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Electroluminescence: the emission of light as current flows through a system
https://en.wikipedia.org/wiki/Electroluminescence
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Electric Current
We consider an electronic trap where single electrons interact with a cavity mode. Two electronic reservoirs can add or remove electrons from the trap, allowing the flow of current through the system.
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Electric Current Phys. Rev. X 7, 011030 (2017)
For concreteness, you can think of the trap as a double quantum dot device in the Coulomb blockade regime: which allows one and only one electron inside the system at any time.
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Let us now study the Hilbert Space of this system
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Electric Current
When no electrons are inside the trap there is no light-matter interaction (since there is no matter there). We have a free sector of the Hilbert space whose states are labelled with the letter , and the number n of photons in the cavity. The dynamics describes free photons inside the cavity.
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Electric Current
We assume that one electron inside the trap can be in two states (e.g., left or right dot) which we label as |g> or |e>. The electron interacts with the light through the Rabi Hamiltonian whose eigenstates (ground and higher polaritonic states) can be used to describe the system.
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The Environment: The electronic reservoirs will cause one electron to enter or leavethe system, allowing transitions between the free and interacting sector (green arrows). Light leaking out will only cause transitions within each sector (removing one photon. Yellow arrows below).
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Question: is it possible to have a process which emits extra-cavity radiation without
directly populating any excited state of the light-matter system but only its ground state?
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Electroluminescence
Let us first consider what happens in regular electroluminescence. We start from zero photons in the cavity and no electron in the trap. The chemical potential is set high enough to allow electrons to directly populate excited states.
Regular
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ElectroluminescenceRegular
Indeed, one electron enters the system in an excited state.
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ElectroluminescenceRegular
Indeed, one electron enters the system in an excited state. Eventually this state decays to the ground state emitting electroluminescent radiation outside the cavity.
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ElectroluminescenceRegular
Indeed, one electron enters the system in an excited state. Eventually this state decays to the ground state emitting electroluminescent radiation outside the cavity. The electron then finally leaves the system. We have produced radiation after populating a light-matter excited state.
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ElectroluminescenceRegular Ground State
We now start again with no photons and no electrons. However, we now tune the chemical potential so that electrons can only populate the ground state.
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ElectroluminescenceRegular Ground State
Indeed the electron enters the system in the ground state, which cannot decay.
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ElectroluminescenceRegular Ground State
Indeed the electron enters the system in the ground state, which cannot decay. However, in the ultra-strong coupling regime, the ground state has a component with one photon!
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ElectroluminescenceRegular Ground State
In the ultra-strong coupling regime, the ground state has a component with one photon! There is then a finite probability (α η2) that the electron tunnels out leaving one photon inside the system. The |1,e⟩ becomes when the electron leaves the system.
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ElectroluminescenceRegular Ground State
Which can only now decay emitting ground state electroluminescent radiation.
Note that the emitted photon has a frequency ω+ ω−
while it is ωC = ωCavityin the new case here
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Distinguishing Features:
The ground-state extra-cavity radiation has several features which distinguish it from the regular channel.
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Emission Properties:
Emission Spectrum Dependency on Chemical Potential
The emission spectrum is qualitativelydifferent from the regular channel. E.g., inthe regular (GND-state) channel, electro-luminescence radiation is emitted at thepolaritonic |+/−⟩ (cavity) frequency.
There is a very close relationship betweenemission and electronic transmissionproperties. T = Total emission.
regular
GND state
Thermal (one mode only inside the cavity)
regular Ground state
|+>|−>
|−> |+>
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How to quickly calculate these results numerically?
Numerical results obtained with our software QuTiP
QuTiP = Quantum Toolbox in Python(our popular software has been mentioned in The Economist, Nature, etc.)
To check the possibility for ground state electroluminescence,we performed numerical simulations using QuTiP.
Let us now see portion of the actual code used for this work.
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It is straightforward to define the Hilbert space and the relevant operators.
Rabi Hamiltonian
QuTiP
N = Maximum number of photons in the cavityqeye = identity acting on 3 levels. s-level plus the qubit.
= Non Interacting = |s>< s|.
σz = |e><e| - |g><g|
σx = |e><g| + |g><e|
= H(g) = H(Ω) = Rabi Hamiltonian ( coupling)
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It is straightforward to define the Hilbert space and the relevant operators.
Incidentally, several groups are using QuTiP without citing it.Please cite both QuTiP papers when you use this software for your research.
QuTiP
N = Maximum number of photons in the cavityqeye = identity acting on 3 levels. s-level plus the qubit.
= Non Interacting = |s>< s|.
σz = |e><e| - |g><g|
σx = |e><g| + |g><e|
= H(g) = H(Ω) = Rabi Hamiltonian ( coupling)
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Energy spectrum
We can then compute the eigen-spectrum with a single line of code and then plot it.
Interacting sector(hybridization)
Chemical potential for regular electroluminescence
Chemical potential enough for ground-state electroluminescence
|+>
|0,s>
|G>
|2,s>
|1,s>
|−>|3,s>
= Normalized Rabi frequency ~ coupling strength
QuTiP
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Lindblad operators in the ultra-strong coupling regime
We can then calculate the emission spectrum by properly defining the Lindblad operators by the Fermi golden rule.
QuTiP
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Lindblad operators in the ultra-strong coupling regime
We can then calculate the emission spectrum by properly defining the Lindblad operators by Fermi golden rule.
QuTiP
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Lindblad operators in the ultra-strong coupling regime
We can then calculate the emission spectrum by properly defining the Lindblad operators by Fermi golden rule.
QuTiP
H_in adds 1 electron and H_out removes it. (3,1) = |g> , (3,0) = |s> , (3,0)_dag = <s|
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Lindblad operators in the ultra-strong coupling regime
We can then calculate the emission spectrum by properly defining the Lindblad operators by Fermi golden rule.
QuTiP
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Lindblad operators in the ultra-strong coupling regime
We can then calculate the emission spectrum by properly defining the Lindblad operators by Fermi golden rule.
QuTiP
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We can then finally plot the spectrum.
QuTiP
regular
GND state
|+>|−>
Thermal (one mode only inside the cavity)
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Conclusions
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Ground State Electroluminescence
Normal Electroluminescence
Electroluminescence: the emission of light as current flows through a system
the current populates excited states of the system
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Ground State Electroluminescence
Electroluminescence: the emission of light as current flows through a system
Weak Ultra-Strong
Normal Electroluminescence
the current populates excited states of the system
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Ground State Electroluminescence
Normal Electroluminescence Ground State Electroluminescence
Electroluminescence: the emission of light as current flows through a system
the current populates excited states of the system
Current populates only the ground state andvirtual photons are converted to real photons
Weak Ultra-Strong
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Ground state electroluminescence
Are there ways to probe the ground state structure without destroying its internal coherences?
Using a mechanical oscillator as a probe for virtual photons in the dressed ground state
Ground-state electroluminescence can be seen as a way to probe the coherent structure of the light-matter ground state. However, each time a photon is emitted, all the internal coherences are destroyed. As other methods based on non-adiabatic modulations of the light-matter coupling, ground state electroluminesence is highly disruptive. As a natural follow up, we asked:
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Ground State Electroluminescence Amplified Transduction of Virtual Radiation Pressure
Two methods to directly probe the virtual photons in the light-matter ground state in the ultra-strong coupling regime.
Conclusions
Phys. Rev. Lett. 116, 113601 (2016) Phys. Rev. Lett. 119, 053601 (2017)
By allowing a current to modulate thelight-matter coupling, virtual photons canbe emitted as electroluminescent radiation.
By adding a mechanical probe to thesystem, virtual photons can be detected bythe radiation pressure force.
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Brief Introduction to Cavity Quantum Electrodynamics
Ground-State Physics of light-matter systems in the ultra-strong coupling regime
Summary
Ground State ElectroluminescencePhys. Rev. Lett. 116, 113601 (2016)
Phys. Rev. Lett. 119, 053601 (2017)
Opto-mechanical transduction of virtual radiation pressure
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Cavity Quantum Electrodynamics Opto-mechanics
Hybrid systems
Nature 464, 697-703, 2010 Nature 482, 63-67, 2012
Nature 475, 359 (2011)
S. Haroche groupNature 458, (2009)
Nat. Phys. 6 (2010)
Signal Primary Transducer
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with
We considered the same cavity QED setting as before (one atom inside a cavity). However, we now let one of the cavity mirrors free to move in a harmonic potential.The position of the mirror modulates the length of the cavity which, in turn, modulates its frequency. Expanding at first order we obtain the optomechanicalcoupling between light and mechanics which describes radiation pressure.
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“Virtual” Radiation Pressure
Radiation pressure
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This force induces a mechanical displacement
photons in the cavity exert a radiation pressure force
“Virtual” Radiation Pressure
Radiation pressure
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This force induces a mechanical displacement
photons in the cavity exert a radiation pressure force
“Virtual” Radiation Pressure
At zero temperature
For weak light-matter couplings
the cavity contains no photons
Radiation pressure
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This force induces a mechanical displacement
photons in the cavity exert a radiation pressure force
“Virtual” Radiation Pressure
light-matter system has virtual photons In the ultra-strong coupling regime
Signal:Zero temperature/Ground-state
Displacement At zero temperature
Radiation pressure
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Encouraging, but requires
• A regime not currently reachable
Probing “Virtual” Radiation Pressure?
The signal is non-zero which is encouraging. However, when we compare it withthe zero point motion of the oscillator we notice that the signal is quite weak. Asignal bigger than the zero point motion would require a ultra-strong/deepopto-mechanical coupling.
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Amplification
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We considered to parametrically modulate the light-matter coupling at themechanical frequency.
Intuitively, this parametric dependence turns the virtual radiation pressure into adriving force.Since any response to a drive is proportional to the mechanical susceptibility, weexpect an amplification of the signal given by the mechanical quality factor
Amplification
No modulation
With modulation
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Signal amplified by the Quality Factor
In this way, we get a signal amplified by the mechanicalquality factor, making it, in principle, feasible to bemeasured in state-of-the-art experiments.
Amplification
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(Possible) Physical Implementations
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with
Opto-mechanical coupling
Modulation of the opto-mechanical coupling
J. D. Teufel, Nature 475, 359 (2011)
Nat. Phys. 6 (2010)
In circuit-QED, we can consider the harmonic mode of an LC circuit interacting with anartificial atom. By modulating the capacitance with a mechanical membrane, it is possibleto achieve mechanics/light coupling. By further modulating the kinetic inductance of thecircuit, it can be possible to further modulate the opto-mechanical coupling.
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Conclusions
• Hybrid system that probes virtual photons with a mechanical transducer.
• This signal can be amplified by modulating the opto-mechanical coupling.
• The measurement minimally disturbs the light-matter system.
• Extensions of this protocol could be used to directly probe the light-matter ground state in the deep-coupling regime.
• This amplification technique can be used in other contexts to detect weak constant forces.
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Ground State Electroluminescence Amplified Transduction of Virtual Radiation Pressure
Two methods to directly probe the virtual photons in the light-matter ground state in the ultra-strong coupling regime.
Conclusions
Phys. Rev. Lett. 116, 113601 (2016) Phys. Rev. Lett. 119, 053601 (2017)
By allowing a current to modulate thelight-matter coupling, virtual photons canbe emitted as electroluminescent radiation.
By adding a mechanical probe to thesystem, virtual photons can be detected bythe radiation pressure force.
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THANK YOU FOR YOUR ATTENTIONBelow is a photo of a sunset behind Mount Fuji, as seen from our office building.