Persistent currents in coherently coupled Bose-Einstein condensates in a ring trap

TL;DR

This paper investigates the stability and decay mechanisms of persistent currents in coherently coupled Bose-Einstein condensates confined in a ring trap, revealing how interactions and Rabi frequency influence vortex nucleation and decay.

Contribution

It provides a detailed analysis of decay mechanisms in coherently coupled BECs, highlighting the role of excitation spectra and phase transitions in current stability.

Findings

Decay via density channel involves roton-like minima and vortex nucleation.

Spin-density excitations lead to finite wavelength instabilities.

Near phase transition, a stable state with broken rotational symmetry emerges.

Abstract

We study the stability of persistent currents in a coherently coupled quasi-2D Bose-Einstein condensate confined in a ring trap at T=0. By numerically solving Gross-Pitaevskii equations and by analyzing the excitation spectrum obtained from diagonalization of the Bogoliubov-de Gennes matrix, we describe the mechanisms responsible for the decay of the persistent currents depending on the values of the interaction coupling constants and the Rabi frequency. When the unpolarized system decays due to an energetic instability in the density channel, the spectrum may develop a roton-like minimum, which gives rise to the finite wavelength excitation necessary for vortex nucleation at the inner surface. When decay in the unpolarized system is driven by spin-density excitations, the finite wavelength naturally arises from the existence of a gap in the excitation spectrum. In the polarized phase of the coherently coupled condensate, there is an hybridization of the excitation modes that leads to complex decay dynamics. In particular, close to the phase transition, a state of broken rotational symmetry is found to be stationary and stable.