Phase Transitions in the Anisotropic Dicke-Stark Model with $A$-square terms

TL;DR

This paper demonstrates that superradiant phase transitions can occur in an anisotropic Dicke-Stark model with A-square terms by tuning couplings and adding Stark interactions, overcoming the no-go theorem.

Contribution

It introduces a novel anisotropic Dicke-Stark model that allows superradiant phase transitions by tuning couplings and including Stark terms, bypassing the no-go theorem.

Findings

Superradiant phase transitions occur at zero and finite temperatures.

Critical coupling decreases with isotropic constant and can be zero with strong Stark coupling.

Phase transitions share the same universality class as the original Dicke model.

Abstract

The superradiant phase transition (SRPT) is forbidden in the standard isotropic Dicke model due to the so-called no-go theorem induced by A-square term. In the framework of the Dicke model, we demonstrate that SRPTs can occur at both zero and finite temperatures if we intrinsically tune the rotating wave and count-rotating atom-cavity coupling independently, and/or introduce the nonlinear Stark coupling terms, thus overcoming the no-go theorem. The phase transitions in this so-called anisotropic Dicke-Stark model share the same universality class with the original Dicke model. The critical coupling strength of this model decreases with the isotropic constant gradually, but can be driven to zero quickly with the strong nonlinear Stark coupling. We believe that we have proposed a feasible scheme to observe the SRPT in the future solid-state experiments.