Dissipation-induced bistability in the two-photon Dicke model

TL;DR

This paper explores how dissipation influences phase transitions and stability in the two-photon Dicke model, revealing a complex phase diagram with bistability and different stability regimes.

Contribution

It provides the first analytical study of dissipation effects on the two-photon Dicke model's phase diagram using mean-field approximation.

Findings

Dissipation induces a first-order phase transition to superradiance.

The phase diagram includes stable, bistable, and unstable phases.

Spectral collapse is affected by dissipation, altering stability.

Abstract

The Dicke model is a paradigmatic quantum-optical model describing the interaction of a collection of two-level systems with a single bosonic mode. Effective implementations of this model made it possible to observe the emergence of superradiance, i.e., cooperative phenomena arising from the collective nature of light-matter interactions. Via reservoir engineering and analogue quantum simulation techniques, current experimental platforms allow us not only to implement the Dicke model, but also to design more exotic interactions, such as the two-photon Dicke model. In the Hamiltonian case, this model presents an interesting phase diagram characterized by two quantum criticalities: a superradiant phase transition and a spectral collapse, that is, the coalescence of discrete energy levels into a continuous band. Here, we investigate the effects of both qubit and photon dissipation on the phase transition and on the instability induced by the spectral collapse. Using a mean-field decoupling approximation, we analytically obtain the steady-state expectation values of the observables signaling a symmetry breaking, identifying a first-order phase transition from the normal to the superradiant phase. Our stability analysis unveils a very rich phase diagram, which features stable, bistable, and unstable phases depending on dissipation rate.