Searcharxiv⌕ Search

arXiv subjects

Christophe Salomon

Publications and source records attributed to Christophe Salomon.

At least 19 recordsLinked to original sources
arXiv2024

A Multi-Purpose Platform for Analog Quantum Simulation

Atom-based quantum simulators have had tremendous success in tackling challenging quantum many-body problems, owing to the precise and dynamical control that they provide over the systems' parameters. They are, however, often optimized to address a specific type of problems. Here, we present the design and implementation of a $^6$Li-based quantum gas platform that provides wide-ranging capabilities and is able to address a variety of quantum many-body problems. Our two-chamber architecture relies on a robust and easy-to-implement combination of gray molasses and optical transport from a laser-cooling chamber to a glass cell with excellent optical access. There, we first create unitary Fermi superfluids in a three-dimensional axially symmetric harmonic trap and characterize them using in situ thermometry, reaching temperatures below 20 nK. This allows us to enter the deep superfluid regime with samples of extreme diluteness, where the interparticle spacing is sufficiently large for direct single-atom imaging. Secondly, we generate optical lattice potentials with triangular and honeycomb geometry in which we study diffraction of molecular Bose-Einstein condensates, and show how going beyond the Kapitza-Dirac regime allows us to unambiguously distinguish between the two geometries. With the ability to probe quantum many-body physics in both discrete and continuous space, and its suitability for bulk and single-atom imaging, our setup represents an important step towards achieving a wide-scope quantum simulator.

cond-mat.quant-gas↗
arXiv2021

In Situ Thermometry of Fermionic Cold-Atom Quantum Wires

We study ensembles of fermionic cold-atom quantum wires with tunable transverse mode population and single-wire resolution. From in situ density profiles, we determine the temperature of the atomic wires in the weakly interacting limit and reconstruct the underlying potential landscape. By varying atom number and temperature, we control the occupation of the transverse modes and study the 1D-3D crossover. In the 1D limit, we observe an increase of the reduced temperature $T/T_{F}$ at nearly constant entropy per particle $S/N k_{B}$. The ability to probe individual atomic wires in situ paves the way to quantitatively study equilibrium and transport properties of strongly interacting 1D Fermi gases.

cond-mat.quant-gas↗
arXiv2018

Space QUEST mission proposal: Experimentally testing decoherence due to gravity

Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum properties, such as entanglement, may exhibit entirely different behavior to purely classical systems. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph and coworkers [T C Ralph, G J Milburn, and T Downes, Phys. Rev. A, 79(2):22121, 2009, T C Ralph and J Pienaar, New Journal of Physics, 16(8):85008, 2014], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's (ESA) Space QUEST (Space - Quantum Entanglement Space Test) mission, and study the feasibility of the mission schema.

quant-ph↗
arXiv2016

Connecting few-body inelastic decay to many-body correlations: a weakly coupled impurity in a resonant Fermi gas

We study three-body recombination in an ultracold Bose-Fermi mixture. We first show theoretically that, for weak inter-species coupling, the loss rate is proportional to Tan's contact. Second, using a 7 Li/ 6 Li mixture we probe the recombination rate in both the thermal and dual superfluid regimes. We find excellent agreement with our model in the BEC-BCS crossover. At unitarity where the fermion-fermion scattering length diverges, we show that the loss rate is proportional the 4/3 power of the fermionic density. Our results demonstrate that impurity-induced losses can be used as a quantitative probe of many-body correlations.

cond-mat.quant-gas↗
arXiv2016

Strongly correlated Bose gases

The strongly interacting Bose gas is one of the most fundamental paradigms of quantum many-body physics and the subject of many experimental and theoretical investigations. We review recent progress on strongly correlated Bose gases, starting with a description of beyond mean-field corrections. We show that the Efimov effect leads to non universal phenomena and to a metastability of the low temperature Bose gas through three-body recombination to deeply bound molecular states. We outline differences and similarities with ultracold Fermi gases, discuss recent experiments on the unitary Bose gas, and finally present a few perspectives for future research.

cond-mat.quant-gas↗
arXiv2016

Analog Simulation of Weyl Particles with Cold Atoms

We study theoretically, numerically, and experimentally the relaxation of a collisionless gas in a quadrupole trap after a momentum kick. The non-separability of the potential enables a quasi thermalization of the single particle distribution function even in the absence of interactions. Suprinsingly, the dynamics features an effective decoupling between the strong trapping axis and the weak trapping plane. The energy delivered during the kick is redistributed according to the symmetries of the system and satisfies the Virial theorem, allowing for the prediction of the final temperatures. We show that this behaviour is formally equivalent to the relaxation of massless relativistic Weyl fermions after a sudden displacement from the center of a harmonic trap.

cond-mat.quant-gas↗
arXiv2015

Critical Velocity and Dissipation of an ultracold Bose-Fermi Counterflow

We study the dynamics of counterflowing bosonic and fermionic lithium atoms. First, by tuning the interaction strength we measure the critical velocity vc of the system in the BEC-BCS crossover in the low temperature regime and we compare it to the recent prediction of Castin et al., Comptes Rendus Physique, 16, 241 (2015). Second, raising the temperature of the mixture slightly above the superfluid transitions reveals an unexpected phase-locking of the oscillations of the clouds. We interpret this observation as resulting from a Zeno-like effect induced by dissipation.

cond-mat.quant-gas↗
arXiv2015

Universal Loss Dynamics in a Unitary Bose Gas

The low temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here we first present a theoretical model that describes the dynamic competition between two-body evaporation and three-body re-combination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal magic trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the 2D evaporation case. Experiments performed with unitary 133 Cs and 7 Li atoms fully support our predictions and enable quantitative measurements of the 3-body recombination rate in the low temperature domain. In particular, we measure for the first time the Efimov inelasticity parameter $η$ * = 0.098(7) for the 47.8-G d-wave Feshbach resonance in 133 Cs. Combined 133 Cs and 7 Li experimental data allow investigations of loss dynamics over two orders of magnitude in temperature and four orders of magnitude in three-body loss. We confirm the 1/T 2 temperature universality law up to the constant $η$ *.

cond-mat.quant-gas↗
arXiv2015

Simultaneous sub-Doppler laser cooling of fermionic $^6$Li and $^{40}$K on the D$_1$ line: Theory and Experiment

We report on simultaneous sub-Doppler laser cooling of fermionic $^6$Li and $^{40}$K using the D$_1$ optical transitions. We compare experimental results to a numerical simulation of the cooling process applying a semi-classical Monte Carlo wavefunction method. The simulation takes into account the three dimensional optical molasses setup and the dipole interaction between atoms and the bichromatic light field driving the D$_1$ transitions. We discuss the physical mechanisms at play, we identify the important role of coherences between the ground state hyperfine levels and compare D$_1$ and D$_2$ sub-Doppler cooling. In 5 ms, the D$_1$ molasses phase largely reduces the temperature for both $^6$Li and $^{40}$K at the same time, with a final temperature of 44 $μ$K and 11 $μ$K, respectively. For both species this leads to a phase-space density close to $10^{-4}$. These conditions are well suited to directly load an optical or magnetic trap for efficient evaporative cooling to quantum degeneracy.

physics.atom-ph↗
arXiv2014

A Mixture of Bose and Fermi Superfluids

Superconductivity and superfluidity of fermionic and bosonic systems are remarkable many-body quantum phenomena. In liquid helium and dilute gases, Bose and Fermi superfluidity has been observed separately, but producing a mixture in which both the fermionic and the bosonic components are superfluid is challenging. Here we report on the observation of such a mixture with dilute gases of two Lithium isotopes, 6Li and 7Li. We probe the collective dynamics of this system by exciting center-of-mass oscillations that exhibit extremely low damping below a certain critical velocity. Using high precision spectroscopy of these modes we observe coherent energy exchange and measure the coupling between the two superfluids. Our observations can be captured theoretically using a sum-rule approach that we interpret in terms of two coupled oscillators.

cond-mat.quant-gas↗
arXiv2013

Realizing a Kondo-correlated state with ultracold atoms

We propose a novel realization of Kondo physics with ultracold atomic gases. It is based on a Fermi sea of two different hyperfine states of one atom species forming bound states with a different species, which is spatially confined in a trapping potential. We show that different situations displaying Kondo physics can be realized when Feshbach resonances between the species are tuned by a magnetic field and the trapping frequency is varied. We illustrate that a mixture of ${}^{40}$K and ${}^{23}$Na atoms can be used to generate a Kondo correlated state and that momentum resolved radio frequency spectroscopy can provide unambiguous signatures of the formation of Kondo resonances at the Fermi energy. We discuss how tools of atomic physics can be used to investigate open questions for Kondo physics, such as the extension of the Kondo screening cloud.

cond-mat.str-el↗
arXiv2013

Λ-enhanced Sub-Doppler Cooling of Lithium Atoms in D1 Gray Molasses

Following the bichromatic sub-Doppler cooling scheme on the D1 line of 40K recently demonstrated in (Fernandes et al. 2012), we introduce a similar technique for 7Li atoms and obtain temperatures of 60 uK while capturing all of the 5x10^8 atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified, Λ-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of ~10^-5. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.

physics.atom-ph↗
arXiv2013

Condensation Energy of a Spin-1/2 Strongly Interacting Fermi Gas

We report a measurement of the condensation energy of a two-component Fermi gas with tunable interactions. From the equation of state of the gas, we infer the properties of the normal phase in the zero-temperature limit. By comparing the pressure of the normal phase at T=0 to that of the low-temperature superfluid phase, we deduce the condensation energy, i.e. the energy gain of the system in being in the superfluid rather than normal state. We compare our measurements to a ladder approximation description of the normal phase, and to a fixed node Monte-Carlo approach, finding excellent agreement. We discuss the relationship between condensation energy and pairing gap in the BEC-BCS crossover.

cond-mat.quant-gas↗
arXiv2013

2.1-watts intracavity-frequency-doubled all-solid-state light source at 671 nm for laser cooling of lithium

We present an all-solid-state laser source emitting up to 2.1 W of single-frequency light at 671 nm developed for laser cooling of lithium atoms. It is based on a diode-pumped, neodymium-doped orthovanadate (Nd:YVO$_4$) ring laser operating at 1342 nm. Optimization of the thermal management in the gain medium results in a maximum multi-frequency output power of 2.5 W at the fundamental wavelength. We develop a simple theory for the efficient implementation of intracavity second harmonic generation, and its application to our system allows us to obtain nonlinear conversion efficiencies of up to 88%. Single-mode operation and tuning is established by adding an etalon to the resonator. The second-harmonic wavelength can be tuned over 0.5 nm, and mode-hop-free scanning over more than 6 GHz is demonstrated, corresponding to around ten times the laser cavity free spectral range. The output frequency can be locked with respect to the lithium $D$-line transitions for atomic physics applications. Furthermore, we observe parametric Kerr-lens mode-locking when detuning the phase-matching temperature sufficiently far from the optimum value.

physics.optics↗
arXiv2012

Reply to the comment on: "Does an atom interferometer test the gravitational redshift at the Compton frequency?"

Hohensee, Chu, Peters and Müller have submitted a comment (arXiv:1112.6039 [gr-qc]) on our paper "Does an atom interferometer test the gravitational redshift at the Compton frequency?", Classical and Quantum Gravity 28, 145017 (2011), arXiv:1009.2485 [gr-qc]. Here we reply to this comment and show that the main result of our paper, namely that atom interferometric gravimeters do not test the gravitational redshift at the Compton frequency, remains valid.

gr-qc↗
arXiv2011

Three Dimensional Raman Cooling using Velocity Selective Rapid Adiabatic Passage

We present a new and efficient implementation of Raman cooling of trapped atoms. It uses Raman pulses with an appropriate frequency chirp to realize a velocity selective excitation through a rapid adiabatic passage. This method allows to address in a single pulse a large number of non zero atomic velocity classes and it produces a nearly unity transfer efficiency. We demonstrate this cooling method using cesium atoms in a far-detuned crossed dipole trap. Three-dimensional cooling of $1 \times 10^{5}$ atoms down to $2 μ$K is performed in 100 ms. In this preliminary experiment the final atomic density is $1.3\times 10^{12}$ at/cm$^3$ (within a factor of 2) and the phase-space density increase over the uncooled sample is 20. Numerical simulations indicate that temperatures below the single photon recoil temperature should be achievable with this method.

cond-mat.quant-gas↗
arXiv2011

Atom interferometry and the Einstein equivalence principle

The computation of the phase shift in a symmetric atom interferometer in the presence of a gravitational field is reviewed. The difference of action-phase integrals between the two paths of the interferometer is zero for any Lagrangian which is at most quadratic in position and velocity. We emphasize that in a large class of theories of gravity the atom interferometer permits a test of the weak version of the equivalence principle (or universality of free fall) by comparing the acceleration of atoms with that of ordinary bodies, but is insensitive to that aspect of the equivalence principle known as the gravitational redshift or universality of clock rates.

gr-qc↗