Single vortex states in a confined Bose-Einstein condensate

TL;DR

This paper theoretically investigates single vortex states in confined Bose-Einstein condensates, analyzing their properties, energies, and relationships to solitonic excitations across different interaction strengths.

Contribution

It provides a numerical and analytical study of vortex excitations, identifying two vortex types, their energy relations, and their connection to solitons in Bose-Einstein condensates.

Findings

Two vortex types, S-vortex and U-vortex, exhibit different precession frequencies.

Vortex line bending and frequency shifts occur with increasing interaction strength.

S-vortex has higher energy than U-vortex in elongated condensates at the same angular momentum.

Abstract

It has been demonstrated experimentally that non-axially symmetric vortices precess around the centre of a Bose-Einstein condensate. Two types of single vortex states have been observed, usually referred to as the S-vortex and the U-vortex. We study theoretically the single vortex excitations in spherical and elongated condensates as a function of the interaction strength. We solve numerically the Gross-Pitaevskii equation and calculate the angular momentum as a function of precession frequency. The existence of two types of vortices means that we have two different precession frequencies for each angular momentum value. As the interaction strength increases the vortex lines bend and the precession frequencies shift to lower values. We establish that for given angular momentum the S-vortex has higher energy than the U-vortex in a rotating elongated condensate. We show that the S-vortex is related to the solitonic vortex which is a nonlinear excitation in the nonrotating system. For small interaction strengths the S-vortex is related to the dark soliton. In the dilute limit a lowest Landau level calculation provides an analytic description of these vortex modes in terms of the harmonic oscillator states.