Stuttgart 2012 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 14: Quantengase: Bosonen 2

Q 14.6: Talk

Monday, March 12, 2012, 17:45–18:00, V47.02

(contribution withdrawn) Thermodynamics and Superfluidity of a 2D Bose Gas — Rémi Desbuquois, Lauriane Chomaz, •Christof Weitenberg, Julian Leonard, Tarik Yefsah, Jérôme Beugnon, and Jean Dalibard — Laboratoire Kastler Brossel, CNRS, UPMC, Ecole Normale Supérieure, 24 rue Lhomond, F-75005 Paris, France

Using in situ measurements on a quasi two-dimensional, harmonically trapped 87Rb gas, we infer various equations of state for the equivalent homogeneous fluid. From the dependence of the total atom number and the central density of our clouds with the chemical potential and temperature, we obtain the equations of state for the pressure and the phase-space density. Then using the approximate scale invariance of this two-dimensional system, we determine the entropy per particle. We measure values as low as 0.06 kB in the strongly-degenerate regime, which shows that a 2D Bose gas can constitute an efficient coolant for other quantum fluids.

Moreover, we investigate the superfluidity of the trapped two-dimensional gas. We use a micron-sized laser beam as an obstacle and stir in a circle centered on the gas, thus perturbing at fixed chemical potential. By varying the stirring velocity and monitoring the heating of the system, we can detect the Landau critical velocity, at which dissipation sets it. The critical velocity is limited by the local speed of sound and is therefore a measure for the local superfluid density. By repeating the experiment at different stirring radii we want to explore regions of different local chemical potential and therefore map out the jump of the superfluid density at the BKT transition.