Multicritical dissipative phase transitions in the anisotropic open quantum Rabi model

TL;DR

This paper explores the complex phase behavior of the anisotropic open quantum Rabi model, revealing multicritical points, bistability, and new critical exponents, with potential experimental realization in trapped ion systems.

Contribution

It uncovers the rich phase diagram of the anisotropic quantum Rabi model, identifying multicritical points and deriving new critical exponents through combined semiclassical and quantum analyses.

Findings

Existence of bistable phase with normal and superradiant states

Identification of multicritical points where phase boundaries meet

Proposal for observing transitions in trapped ion experiments

Abstract

We investigate the nonequilibrium steady state of the anisotropic open quantum Rabi model, which exhibits first-order and second-order dissipative phase transitions upon varying the degree of anisotropy between the coupling strengths of rotating and counterrotating terms. Using both semiclassical and quantum approaches, we find a rich phase diagram resulting from the interplay between the anisotropy and the dissipation. First, there exists a bistable phase where both the normal and superradiant phases are stable. Second, there are multicritical points where the phase boundaries for the first- and second-order phase transitions meet. We show that a new set of critical exponents governs the scaling of the multicritical points. Finally, we discuss the feasibility of observing the multicritical transitions and bistability using a pair of trapped ions where the anisotropy can be tuned by controlling the intensity of the Raman transitions. Our study enlarges the scope of critical phenomena that may occur in finite-component quantum systems, which could be useful for applications in critical quantum sensing.