Two-dimensional dynamics of expansion of a degenerate Bose gas

TL;DR

This study numerically investigates the expansion dynamics of a degenerate Bose gas in two dimensions, considering phase fluctuations and interactions, but finds discrepancies with experimental scaling laws, suggesting the need for further theoretical explanation.

Contribution

It introduces a two-dimensional numerical simulation of Bose gas expansion incorporating phase noise and interactions, highlighting limitations of current models in explaining experimental results.

Findings

Numerical simulations did not reproduce the experimental scaling law.

Finite size and atomic interactions significantly affect early expansion dynamics.

Current models may need refinement to match experimental observations.

Abstract

Expansion of a degenerate Bose gas released from a pancakelike trap is numerically simulated under the assumption of separation of the motion in the plane of the loose initial trapping and the motion in the direction of the initial tight trapping. The initial conditions for the phase fluctuations are generated using the extension to the two-dimensional case of the description of the phase noise by the Ornstein-Uhlenbeck stochastic process. The numerical simulations, taking into account both the finite size of the two-dimensional system and the atomic interactions, which cannot be neglected on the early stage of expansion, did not reproduce the scaling law for the peaks in the density fluctuation spectra experimentally observed by Choi, Seo, Kwon, and Shin [Phys. Rev. Lett. 109, 125301 (2012)]. The latter experimental results may thus require an explanation beyond our current assumptions.