Non-equilibrium dynamics of a 2D Bose gas near a critical point

We report experimental measurements of the relaxation dynamics of 2D Bose gases following the coherent splitting into two 2D clouds. The splitting of low-dimensional ultracold gases produces a non-equilibrium initial state with spatially uniform relative phase; the transformation from a single- to a double-well potential is implemented by applying RF radiation at multiple frequencies to form dressed states of Rb-87 atoms in a magnetic quadrupole field and by dynamically modulating the RF amplitudes [1]. The relative phase of the two clouds is detected by imaging the cross-section of matter-wave interference after Time-of-Flight expansion [1].

In our experiment, the reduction of density in the splitting process quenches the system close to the Berezinskii-Kosterlitz-Thouless critical point. Related experiments have been carried out with 1D clouds [2].

[1] A. J. Barker, S. Sunami, D. Garrick, A. Beregi, K. Luksch, E. Bentine and C. J. Foot. New J. Phys. 22 103040 (2020)
[2] T. Langen, T. Gasenzer and J. Schmiedmayer. J. Stat. Mech. 064009 (2016)