Two-fluid hydrodynamics of a Bose gas including damping from normal fluid transport coefficients

TL;DR

This paper extends two-fluid hydrodynamics of a Bose gas by incorporating damping effects from viscosity and thermal conduction, predicting new damped modes and providing insights into dissipative processes in Bose-Einstein condensates.

Contribution

It introduces dissipation into two-fluid hydrodynamics of Bose gases, including viscosity and thermal conduction, and predicts new damped modes not present in standard models.

Findings

Damping of first and second sound modes due to viscosity and thermal conductivity.

Existence of a strongly coupled relaxational mode at zero frequency.

Prediction of a damped mode at zero frequency, unlike standard models.

Abstract

We extend our recent work on the two-fluid hydrodynamics of the condensate and non-condensate in a trapped Bose gas by including the dissipation associated with viscosity and thermal conduction. For purposes of illustration, we consider the hydrodynamic modes in the case of a uniform Bose gas. A finite thermal conductivity and shear viscosity give rise to a damping of the first and second sound modes in addition to that found previously due to the lack of diffusive equilibrium between the condensate and non-condensate. The relaxational mode associated with this equilibration process is strongly coupled to thermal fluctuations and reduces to the usual thermal diffusion mode above the Bose-Einstein transition. In contrast to the standard Landau two-fluid hydrodynamics, we predict a damped mode centered at zero frequency, in addition to the usual second sound doublet.