Vortices in self-bound dipolar droplets

TL;DR

This paper investigates the stability of vortex lines in self-bound dipolar droplets, revealing their instability through simulations and discussing experimental observation possibilities.

Contribution

It provides the first detailed analysis of vortex stability in dipolar droplets using a generalized nonlocal Gross-Pitaevskii model with quantum fluctuations.

Findings

Vortex states exist within a wide stability region.

Singly-charged vortices are unstable, splitting or developing Kelvin-wave instabilities.

Large-scale 3D simulations confirm vortex instability mechanisms.

Abstract

Quantized vortices have been observed in a variety of superfluid systems, from $^4$He to condensates of alkali-metal bosons and ultracold Fermi gases along the BEC-BCS crossover. In this article we study the stability of singly quantized vortex lines in dilute dipolar self-bound droplets. We first discuss the energetic stability region of dipolar vortex excitations within a variational ansatz in the generalized nonlocal Gross-Pitaevskii functional that includes quantum fluctuation corrections. We find a wide region where stationary solutions corresponding to axially-symmetric vortex states exist. However, these singly-charged vortex states are shown to be unstable, either by splitting the droplet in two fragments or by vortex-line instabilities developed from Kelvin-wave excitations. These observations are the results of large-scale fully three-dimensional simulations in real time. We conclude with some experimental considerations for the observation of such states and suggest possible extensions of this work.