Vortex excitation in a stirred toroidal Bose-Einstein condensate

TL;DR

This paper models vortex formation in a stirred toroidal Bose-Einstein condensate, revealing how vortex-antivortex pairs and surface modes develop depending on stirring speed, aligning with recent experimental findings.

Contribution

It provides a detailed mean field analysis of vortex excitation mechanisms in a toroidal BEC under stirring, matching experimental conditions and identifying critical velocities for vortex formation.

Findings

Vortex-antivortex pairs form near the stirrer at slow speeds.

Outer edge surface modes develop above a critical stirring velocity.

Vortex entry into the condensate depends on stirring parameters.

Abstract

Motivated by the recent experiment [Wright et al., Phys. Rev. A 88, 063633 (2013)], we investigate formation of vortices in an annular BEC stirred by a narrow blue-detuned optical beam. In the framework of a two-dimensional mean field model, we study the dissipative dynamics of the condensate with parameters matched to the experimental conditions. Vortex-antivortex pairs appear near the center of the stirrer in the bulk of the condensate for slow motion of the stirring beam. When the barrier angular velocity is above some critical value, an outer edge surface mode develops and breaks into the vortices entering the condensate annulus. We determine the conditions for creation of the vortex excitations in the stirred toroidal condensate and compare our results with the experimental observations.