Chiral Quantum Droplet in a Spin-Orbit Coupled Bose Gas

TL;DR

This paper demonstrates the formation of a chiral quantum droplet in a spin-orbit coupled Bose gas, highlighting how broken Galilean invariance enables direction-dependent self-binding and phase transitions.

Contribution

It introduces the concept of chiral quantum droplets arising from spin-orbit coupling, showing how velocity and spin polarization induce self-binding and phase changes.

Findings

Chiral quantum droplets form only beyond a critical velocity in specific directions.

The phase diagram includes droplet, gas, and coexistence regions for 39K mixtures.

Chirality emerges due to broken Galilean invariance in spin-orbit coupled systems.

Abstract

We report the formation of chiral quantum droplet in a spin-orbit coupled Bose gas, where the system turns to a self-bound droplet when moving towards a particular direction and remains gaseous otherwise. The chirality arises from the breaking of Galilean invariance by spin-orbit coupling, which enables the system to dynamically adjust its condensation momentum and spin polarization in response to its velocity. As a result, only towards a specific moving direction and beyond a critical velocity, the acquired spin polarization can trigger collective interactions sufficient for self-binding and drive a first-order transition from gas to droplet. We have mapped out a phase diagram of droplet, gas and their coexistence for realistic spin-orbit coupled 39K mixtures with tunable moving velocity and magnetic detuning. Our results have revealed the emergence of chirality in spin-orbit coupled quantum gases, which shed light on general chiral phenomena in moving systems with broken Galilean invariance.