LKB - Bose-Einstein condensates

2D rubidium Bose gases

Research

Loading and compression of a single uniform 2D Bose gas in an optical accordion

We implemented on our new setup an optical accordion creating a lattice potential with a spacing  that can be dynamically tuned between 11 and 2 µm. Atoms are loaded into a single node of this optical lattice in the large spacing configuration which is then decreased almost adiabatically to reach a strong harmonic confinement with a frequency larger than 10 kHz. This allows us to tune the effective 2D interaction strength. An additional flat-bottom in-plane potential is shaped with a high resolution thanks to  a spatial light modulator (Digital Micromirror Device) combined with a microscope objective.

References :

J.L. Ville, T. Bienaimé, R. Saint-Jalm, L. Corman, M. Aidelsburger, L. Chomaz, K. Kleinlein, D. Perconte, S. Nascimbène, J. Dalibard, J. Beugnon
Phys. Rev. A 95, 013632 (2017) and arXiv:1611.07681
Loading and compression of a single 2D Bose gas in an optical accordion

Bose gases in box potentials: investigating Kibble-Zurek mechanism

We studied the formation of topological defects when quench cooling Bose gases. Atoms are trapped either in a square box-like potential or in a ring. In the box potential we observed the stochastic formation of vortices (see picture) and in the ring geometry we observed the creation of superfluid currents along the ring. Using matter-wave interference techniques we were able to measure the charge and direction of these currents. We also studied in the box potential the emergence of coherence due to the transverse condensation phase transition. We compared the rate of formation of these topological defects with Kibble-Zurek mechanism predictions.

References :

L. Chomaz, L. Corman, T. Bienaimé, R. Desbuquois, C. Weitenberg, S. Nascimbène, J. Beugnon, J. Dalibard
Nature Commum. 6, 6162 (2015)  and arXiv:1411.3577
Emergence of coherence in a uniform quasi-two-dimensional Bose gas

L. Corman, L. Chomaz, T. Bienaimé, R. Desbuquois, C. Weitenberg, S. Nascimbène, J. Dalibard, and J. Beugnon
Phys. Rev. Lett. 113, 135302 (2014) and arXiv:1406.4073
Quench-Induced Supercurrents in an Annular Bose Gas

Superfluid behavior of a 2D Bose gas

 

We demonstrated the superfluid behavior of a 2D Bose gas confined in a harmonic trap. By rotating a defect created by a repulsive laser beam we measured a threshold velocity for heating the cloud. We observed that this threshold is only present when we rotate in the superfluid inner region and not in the thermal outer region.

References :

R. Desbuquois, L. Chomaz, T. Yefsah, J. Léonard, J. Beugnon, C. Weitenberg, J. Dalibard
Nature Physics 8, 645 (2012) and arXiv:1205.4536
Superfluid behaviour of a two-dimensional Bose gas

Equation of state of the weakly-interacting 2D Bose gas

 

We measured the equation of state of a 2D Bose gas and compared it with theoretical predictions. The method is based on the measurement of the in situ density profile of the cloud trapped in a harmonic potential and the use of the local density approximation. We first used a method based on fitting the density profile to extract the chemical potential and the temperature. We also demonstrated a fit-free method to determine the equation of state.

References :

R. Desbuquois, T. Yefsah, L. Chomaz, C. Weitenberg, L. Corman, S. Nascimbène, J. Dalibard
Phys. Rev. Lett. 113, 020404 (2014) and arXiv:1403.4030
Fit-free determination of scale invariant equations of state: application to the two-dimensional Bose gas

T. Yefsah, R. Desbuquois, L. Chomaz, K. J. Günter, J. Dalibard
Phys. Rev. Lett. 107, 130401 (2011) and arXiv:1106.0188
Exploring the thermodynamics of a two-dimensional Bose gas

S.P. Rath, T. Yefsah, K.J. Günter, M. Cheneau, R. Desbuquois, M. Holzmann, W. Krauth, J. Dalibard
Phys. Rev. A 82, 013609 (2010) and arXiv:1003.4545
The equilibrium state of a trapped two-dimensional Bose gas