Dipolar condensates confined in a toroidal trap: ground state and vortices

TL;DR

This paper investigates how dipolar interactions and trap geometry influence the ground state and vortex structures of a 52Cr Bose-Einstein condensate in a toroidal trap, revealing symmetry breaking and azimuthal density variations.

Contribution

It provides a detailed analysis of dipolar effects on condensate shape, density distribution, and vortex states in a toroidal geometry with variable interactions.

Findings

Density peaks depend on magnetization direction and scattering length.

Symmetry breaking causes density to concentrate in one peak at low scattering lengths.

Vortex velocity fields show azimuthal dependence in the dipolar condensate.

Abstract

We study a Bose-Einstein condensate of 52Cr atoms confined in a toroidal trap with a variable strength of s-wave contact interactions. We analyze the effects of the anisotropic nature of the dipolar interaction by considering the magnetization axis to be perpendicular to the trap symmetry axis. In the absence of a central repulsive barrier, when the trap is purely harmonic, the effect of reducing the scattering length is a tuning of the geometry of the system: from a pancake-shaped condensate when it is large, to a cigar-shaped condensate for small scattering lengths. For a condensate in a toroidal trap, the interaction in combination with the central repulsive Gaussian barrier produces an azimuthal dependence of the particle density for a fixed radial distance. We find that along the magnetization direction the density decreases as the scattering length is reduced but presents two symmetric density peaks in the perpendicular axis. For even lower values of the scattering length we observe that the system undergoes a dipolar-induced symmetry breaking phenomenon. The whole density becomes concentrated in one of the peaks, resembling an origin-displaced cigar-shaped condensate. In this context we also analyze stationary vortex states and their associated velocity field, finding that this latter also shows a strong azimuthal dependence for small scattering lengths. The expectation value of the angular momentum along the z direction provides a qualitative measure of the difference between the velocity in the different density peaks.