Non-Gaussian superradiant transition via three-body ultrastrong coupling

TL;DR

This paper introduces a three-body quantum optical Hamiltonian with non-Gaussian superradiant phase transition, realized via circuit-QED, highlighting novel first-order transition features and robustness against dissipation.

Contribution

It proposes a new three-body coupling model in quantum optics, demonstrating a non-Gaussian superradiant transition with unique symmetry breaking and experimental implementation scheme.

Findings

First-order superradiant phase transition with symmetry breaking

Ground state exhibits divergent coskewness near transition

Robust steady-state features under dissipation

Abstract

We introduce a class of quantum optical Hamiltonian characterized by three-body couplings, and propose a circuit-QED scheme based on state-of-the-art technology that implements the considered model. Unlike two-body light-matter interactions, this three-body coupling Hamiltonian is exclusively composed of terms which do not conserve the particle number. We explore the three-body ultrastrong coupling regime, showing the emergence of a superradiant phase transition which is of first order, is characterized by the breaking of a $\mathbb{Z}_2\times \mathbb{Z}_2$ symmetry and has a strongly non-Gaussian nature. Indeed, in contrast to what is observed in any two-body-coupling model, in proximity of the transition the ground state exhibits a divergent coskewness, i.e., quantum correlations that cannot be captured within semiclassical and Gaussian approximations. Furthermore, we demonstrate the robustness of our findings by including dissipative processes in the model, showing that the steady-state of the system inherits from the ground states the most prominent features of the transition.