Nonreciprocal Superradiant Phase Transitions and Multicriticality in a Cavity QED System

TL;DR

This paper reports on the discovery of nonreciprocal superradiant phase transitions and multicritical points in a cavity QED system influenced by cavity rotation and directional squeezing, enabling controllable light-matter interactions.

Contribution

It introduces a novel cavity QED setup with rotation and squeezing that exhibits nonreciprocal phase transitions and multicriticality without requiring ultrastrong coupling.

Findings

Nonreciprocal first- and second-order superradiant phase transitions observed.

Identification of controllable multicritical points in the phase diagram.

Potential for all-optical manipulation of quantum phase transitions.

Abstract

We demonstrate the emergence of nonreciprocal superradiant phase transitions and novel multicriticality in a cavity quantum electrodynamics (QED) system, where a two-level atom interacts with two counter-propagating modes of a whispering-gallery-mode (WGM) microcavity. The cavity rotates at a certain angular velocity, and is directionally squeezed by a unidirectional parametric pumping $\chi^{(2)}$ nonlinearity. The combination of cavity rotation and directional squeezing leads to nonreciprocal first- and second-order superradiant phase transitions. These transitions do not require ultrastrong atom-field couplings and can be easily controlled by the external pump field. Through a full quantum description of the system Hamiltonian, we identify two types of multicritical points in the phase diagram, both of which exhibit controllable nonreciprocity. These results open a new door for all-optical manipulation of superradiant transitions and multicritical behaviors in light-matter systems, with potential applications in engineering various integrated nonreciprocal quantum devices