arXiv:1807.10721 · Physical Review A
Spectral and dynamical analysis of a single vortex ring in anisotropic harmonically trapped three-dimensional Bose-Einstein condensates
Christopher Ticknor, Wenlong Wang, P. G. Kevrekidis
Abstract
In the present work, motivated by numerous recent experimental developments we revisit the dynamics of a single vortex ring in anisotropic harmonic traps. At the theoretical level, we start from a general Lagrangian dynamically capturing the evolution of a vortex ring and not only consider its spectrum of linearized excitations, but also explore the full nonlinear dynamical evolution of the ring as a vortical filament. The theory predicts that the ring is stable for $1\ensuremath{\le}\ensuremath{\lambda}\ensuremath{\le}2$, where $\ensuremath{\lambda}={\ensuremath{\omega}}_{z}/{\ensuremath{\omega}}_{r}$ is the ratio of the trapping frequencies along the $z$ and $r$ axes, i.e., for spherical to slightly oblate condensates. We compare this prediction with direct numerical simulations of the full three-dimensional Gross-Pitaevskii equation (GPE) capturing the linearization spectrum of the ring for different values of the chemical potential and as a function of the anisotropy parameter $\ensuremath{\lambda}$. We identify this result as being only asymptotically valid as the chemical potential $\ensuremath{\mu}\ensuremath{\rightarrow}\ensuremath{\infty}$, revealing how the stability interval narrows and, in particular, its upper bound decreases for finite $\ensuremath{\mu}$. Finally, we compare at the dynamical level the results of the GPE with the ones effectively capturing the ring dynamics, revealing the unstable evolution for different values of $\ensuremath{\lambda}$, as well as the good agreement between the two.