Collisionless sound in a uniform two-dimensional Bose gas

Abstract

Using linear response theory within the Random Phase Approximation, we investigate the propagation of sound in a uniform two dimensional (2D) Bose gas in the collisionless regime. We show that the sudden removal of a static density perturbation produces a damped oscillatory behavior revealing that sound can propagate also in the absence of collisions, due to mean-field interaction effects. Our analysis points out the crucial role played by Landau damping. We support our predictions by performing numerical simulations with the stochastic (projected) Gross-Pitaevskii equation. The results are consistent with the recent experimental observation of sound in a weakly interacting 2D Bose gas both below and above the superfluid Berezinskii-Kosterlitz-Thouless transition.

arXiv commentMain text: 4 pages, 4 figures + Supplementary material: 2 page. The general structure has been revised for clarity, with improved introduction and conclusions. Accepted for publication in Physical Review Letters

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