Dalibard, Jean

Date: Thursday, April 23, 2015
Time: 15:30
Place: ETH Zurich, Hönggerberg, HPF G 6
Host: Julian Léonhard / Tilman Esslinger

The uniform 2D Bose gas, in and out of equilibrium

Jean Dalibard
Collège de France and Laboratoire Kastler Brossel

Most experimental studies with quantum gases are performed with atoms confined in a harmonic potential. This is well suited for the investigation of some equilibrium properties of the gas, thanks to the local density approximation that relates the properties of the trapped fluid with those of a uniform system with the same local thermodynamic variables. However the non-homogenous density profile of trapped gases prevents one from addressing the part of equilibrium physics related to long-range correlations. This restriction is particularly significant for low dimensional systems, for which one may want to investigate the quasi-long range order that can appear at non zero temperature.

In this talk I will first report on our realization of a uniform quasi-two-dimensional Bose gas confined in a box-like potential. I will then describe experiments addressing the emergence of coherence in the gas when it is cooled across the superfluid transition.  I will present signatures of topological defects (vortices) that are nucleated in the system in the course of the cooling. I will show that the production rate of these defects is directly linked to the cooling rate, and compare our findings with the prediction of the Kibble-Zurek mechanism.

References

[1] L. Corman, L. Chomaz, T. Bienaimé, R. Desbuquois, C. Weitenberg, S. Nascimbene, J. Dalibard, J. Beugnon, Quench-induced supercurrents in an annular two-dimensional Bose gas, Phys. Rev. Lett. 113, 135302 (2014)

[2] Lauriane Chomaz, Laura Corman, Tom Bienaimé, Rémi Desbuquois, Christof Weitenberg, Sylvain Nascimbène, Jérôme Beugnon, Jean Dalibard, Emergence of coherence in a uniform quasi-two-dimensional Bose gas, Nature Commum. 6, 6172 (2015)