Elliptic flow in a strongly-interacting normal Bose gas

TL;DR

This paper investigates the elliptic expansion of a thermal Bose gas across various interaction strengths, demonstrating that a microscopic kinetic model accurately describes the hydrodynamic behavior without free parameters.

Contribution

It introduces a parameter-free microscopic kinetic model that captures the anisotropic expansion dynamics of a strongly interacting Bose gas, including an analytical theory for reduced thermalization.

Findings

Hydrodynamic expansion is fully described by the kinetic model across interaction strengths.

Time-resolved measurements reveal energy transfer dynamics between expansion axes.

Reduced thermalising power in strongly interacting gases is analytically characterized.

Abstract

We study the anisotropic, elliptic expansion of a thermal atomic Bose gas released from an anisotropic trapping potential, for a wide range of interaction strengths across a Feshbach resonance. We show that in our system this hydrodynamic phenomenon is for all interaction strengths fully described by a microscopic kinetic model with no free parameters. The success of this description crucially relies on taking into account the reduced thermalising power of elastic collisions in a strongly interacting gas, for which we derive an analytical theory. We also perform time-resolved measurements that directly reveal the dynamics of the energy transfer between the different expansion axes.