Heterosymmetric states of rotating quantum droplets under confinement

TL;DR

This paper explores the rotational behavior of confined two-dimensional quantum droplets with two components, revealing heterosymmetric states with different vorticities that are missed by simpler models, and analyzing effects of population imbalance.

Contribution

It introduces a two-order-parameter model to study heterosymmetric states in rotating quantum droplets, extending beyond traditional single-parameter approaches.

Findings

Heterosymmetric states occur near half-integer angular momentum values.

Population imbalance lifts degeneracy of heterosymmetric states.

Beyond-mean-field effects favor heterosymmetric modes.

Abstract

We investigate the rotational response of a confined, two-dimensional quantum droplet, which emerges in an attractive binary Bose mixture that is stabilized against collapse by beyond-mean-field effects. We consider both a harmonic and an anharmonic form for the external confining potential. We go beyond the widely employed ``phase-locked" single-order-parameter model, maintaining two separate order parameters for the two components, and calculating the lowest-energy state for various values of the angular momentum. For a population-balanced quantum droplet and sufficiently tight confinement, we find that near certain half-integer values of the angular momentum the droplet is excited in a ``heterosymmetric" manner, with the two components carrying different vorticities. This mode is naturally missed by the single-order-parameter model. We additionally investigate the effects of a small population imbalance in the droplet. Apart from an energy increase associated with the population difference, the imbalance also lifts the double degeneracy of the heterosymmetric states, which characterizes the $\mathbb{Z}_2$-symmetric balanced droplet. The heterosymmetric mode is found to be favored by the energy term which captures the beyond-mean-field effects in the mixture.