LPS (Orsay)

Recent experiments of cold atomic Bose gases trapped in two dimensions using optical lattices successfully studied the Berezinskii-Kosterlitz-Thouless transition, quasi-condensation and its equation of state [1,2,3]. Most of these features fall in the general class of 2D XY models. I will first discuss a mean-field theory for both the normal and quasi-condensate phases of the atomic gas, and show a reduced density-density fluctuation in the latter. We then improve on the mean-field theory with a Wilsonian renormalization group analysis across the transition. Finally, using a local-density approximation, density profiles are obtained for the trapped case, which can be compared with cold gas experiments [4].

 
[1] Z. Hadzibabic et al , Nature 441,1118 (2006).
[2] P. Cladé et al, PRL 102, 170401 (2009).
[3] M. Holzmann and W. Krauth, PRL 100, 190402 (2008).
[4] L.-K. Lim et al, PRA 78, 013634 (2008).