Spinor self-ordering of a quantum gas in a cavity

TL;DR

This paper reports the observation of spinor self-organization in a two-component Bose-Einstein condensate strongly coupled to an optical cavity, revealing a nonequilibrium phase transition driven by cavity-mediated interactions.

Contribution

It demonstrates a novel spinor self-organization process in a quantum gas coupled to a cavity, including the formation of a spinor density-wave polariton condensate and direct phase measurement.

Findings

Observation of spinor self-organization in a BEC-cavity system

Detection of a spinor density-wave polariton condensate

Direct measurement of the cavity field phase and spin domain walls

Abstract

We observe the joint spin-spatial (spinor) self-organization of a two-component BEC strongly coupled to an optical cavity. This unusual nonequilibrium Hepp-Lieb-Dicke phase transition is driven by an off-resonant two-photon Raman transition formed from a classical pump field and the emergent quantum dynamical cavity field. This mediates a spinor-spinor interaction that, above a critical strength, simultaneously organizes opposite spinor states of the BEC on opposite checkerboard configurations of an emergent 2D lattice. The resulting spinor density-wave polariton condensate is observed by directly detecting the atomic spin and momentum state and by holographically reconstructing the phase of the emitted cavity field. The latter provides a direct measure of the spin state, and a spin-spatial domain wall is observed. The photon-mediated spin interactions demonstrated here may be engineered to create dynamical gauge fields and quantum spin glasses.