On the effect of the thermal gas component to the stability of vortices in trapped Bose-Einstein condensates

TL;DR

This paper investigates how the inclusion of thermal gas components in self-consistent mean-field theories stabilizes vortices in trapped Bose-Einstein condensates by lifting negative-energy modes, contrasting with non-self-consistent predictions of vortex instability.

Contribution

It demonstrates that self-consistent theories predict vortex stability through partial filling of the vortex core, highlighting the importance of coupled condensate and noncondensate dynamics.

Findings

Vortices are stabilized by noncondensed gas filling the core.

Self-consistent theories lift anomalous modes to positive energies.

Non-self-consistent Bogoliubov approximation predicts persistent vortex instability.

Abstract

We study the stability of vortices in trapped single-component Bose-Einstein condensates within self-consistent mean-field theories--especially we consider the Hartree-Fock-Bogoliubov-Popov theory and its recently proposed gapless extensions. It is shown that for sufficiently repulsively interacting systems the anomalous negative-energy modes related to vortex instabilities are lifted to positive energies due to partial filling of the vortex core with noncondensed gas. Such a behavior implies that within these theories the vortex states are eventually stable against transfer of condensate matter to the anomalous core modes. This self-stabilization of vortices, shown to occur under very general circumstances, is contrasted to the predictions of the non-self-consistent Bogoliubov approximation, which is known to exhibit anomalous modes for all vortex configurations and thus implying instability of these states. In addition, the shortcomings of these approximations in describing the properties of vortices are analysed, and the need of a self-consistent theory taking properly into account the coupled dynamics of the condensate and the noncondensate atoms is emphasized.