Decay of persistent currents in annular atomic superfluids

TL;DR

This paper studies how vortices cause decay of persistent currents in annular atomic superfluids, using numerical simulations of the Gross-Pitaevskii equation and comparing with experiments, highlighting effects of optical imprinting imperfections and obstacles.

Contribution

It provides a detailed numerical analysis of vortex-induced decay mechanisms in superfluid rings, incorporating realistic optical imprinting and obstacle effects, aligning well with experimental data.

Findings

Imperfect optical imprinting limits maximum winding number.

Critical circulation depends on obstacle height and vortex interactions.

Vortex entry and phase slippage cause supercurrent decay.

Abstract

We investigate the role of vortices in the decay of persistent current states of annular atomic superfluids by solving numerically the Gross-Pitaevskii equation, and we directly compare our results with experimental data from Ref. [1]. We theoretically model the optical phase-imprinting technique employed to experimentally excite finite-circulation states in Ref. [1] in the Bose-Einstein condensation regime, accounting for imperfections of the optical gradient imprinting profile. By comparing simulations of this realistic protocol to an ideal imprinting, we show that the introduced density excitations arising from imperfect imprinting are mainly responsible for limiting the maximum reachable winding number $w_\mathrm{max}$ in the superfluid ring. We also investigate the effect of a point-like obstacle with variable potential height $V_0$ onto the decay of circulating supercurrents. For a given obstacle height, a critical circulation $w_c$ exists, such that for an initial circulation $w_0$ larger than $w_c$ the supercurrent decays through the emission of vortices, which cross the superflow and thus induce phase slippage. Higher values of the obstacle height $V_0$ further favour the entrance of vortices, thus leading to lower values of $w_c$. Furthermore, the stronger vortex-defect interaction at higher $V_0$ leads to vortices that propagate closer to the center of the ring condensate. The combination of both these effects leads to an increase of the supercurrent decay rate for increasing $w_0$, in agreement with experimental observations. [1]: G. Del Pace, et al., Phys. Rev. X 12, 041037 (2022)