# Rashba cavity QED: a route towards the superradiant quantum phase transition

## TL;DR

This paper presents a theoretical framework for Rashba cavity QED, showing that a superradiant quantum phase transition can occur in a 2D electron gas with spin-orbit coupling under realistic conditions.

## Contribution

It introduces a novel theory of cavity QED with Rashba spin-orbit coupling, predicting a superradiant phase transition driven by soft spin-flip transitions.

## Key findings

- Lowest polaritonic frequency can vanish, indicating a superradiant phase transition.
- The transition is linked to magnetostatic instability from non-zero wave vector spin-flip modes.
- The theory applies to realistic experimental parameters.

## Abstract

We develop a theory of cavity quantum electrodynamics for a 2D electron gas in the presence of Rashba spin-orbit coupling and perpendicular static magnetic field, coupled to spatially nonuniform multimode quantum cavity photon fields. We demonstrate that the lowest polaritonic frequency of the full Hamiltonian can vanish for realistic parameters, achieving the Dicke superradiant quantum phase transition. This singular behaviour originates from soft spin-flip transitions possessing a non-vanishing dipole moment at non-zero wave vectors and can be viewed as a magnetostatic instability.