Quantum criticality driven by the cavity coupling in Rabi-dimer model

TL;DR

This paper investigates how inter-cavity coupling in the Rabi-dimer model induces a superradiant phase transition, revealing it belongs to the same universal class as the atom-cavity interaction-driven transition, with analytical and numerical evidence.

Contribution

It analytically derives the phase boundary and characterizes the universal class of the cavity-coupling-driven superradiant phase transition in the Rabi-dimer model.

Findings

Inter-cavity coupling induces a superradiant phase transition.

The transition belongs to the same universality class as atom-cavity interaction.

Ground-state properties confirm the phase transition's nature.

Abstract

The superradiant phase transition (SPT) controlled by the interacting strength between the two-level atom and the photons has been a hot topic in the Rabi model and the Rabi-dimer model. The latter describes two Rabi cavities coupled with an inter-cavity hopping parameter. Moreover, the SPT in the Rabi-dimer model is found to be the same universal class that in the Rabi model by investigating the correlation-length critical exponent. In this paper, we are concerned about whether the inter-cavity hopping parameter between two Rabi cavities (i.e., the Rabi-dimer model) will induce the SPT and to which the universal class of the phase transition belongs. We analytically derive the phase boundary of the SPT and investigate the ground-state properties of the system. We uncover that the inter-cavity induced SPT can be apparently understood from the ground-state energy and the ground-state photon population, as well as the ground-state expectation value of the squared anti-symmetric mode. From the scaling analysis of the fidelity susceptibility, we numerically verify that the SPT driven by the cavity coupling belongs to the same universal class as the one driven by the atom-cavity interaction. Our work enriches the studies on the SPT and its critical behaviors in the Rabi-dimer model.