Vortex Rings in two Component Bose-Einstein Condensates

TL;DR

This paper explores vortex rings, called vortons, in two-component Bose-Einstein condensates, revealing their potential stability at rest due to core condensation, with implications for laboratory cosmology simulations.

Contribution

It demonstrates the existence and stability of vortons in two-component BECs, a phenomenon previously known in particle physics and cosmology, and suggests experimental observation possibilities.

Findings

Vortons can be stable even at rest in two-component BECs.

Core condensation of the second component stabilizes vortex rings.

Potential laboratory observation of cosmological topological structures.

Abstract

We study the structure of the vortex core in two-component Bose-Einstein condensates. We demonstrate that the order parameter may not vanish and the symmetry may not be restored in the core of the vortex. In this case such vortices can form vortex rings known as vortons in particle physics literature. In contrast with well-studied superfluid $^4He$, where similar vortex rings can be stable due to Magnus force only if they move, the vortex rings in two-component BECs can be stable even if they are at rest. This beautiful effect was first discussed by Witten in the cosmic string context, where it was shown that the stabilization occurs due to condensation of the second component of the field in the vortex core. This second condensate trapped in the core may carry a current along the vortex ring counteracting the effect of string tension that causes the loop to shrink. We speculate that such vortons may have been already observed in the laboratory. We also speculate that the experimental study of topological structures in BECs can provide a unique opportunity to study cosmology and astrophysics by doing laboratory experiments.