Dissipative Phase Transitions in an Open Quantum Rabi Model with Two-Photon Processes

Abstract:We demonstrate a novel mechanism driving complex critical phenomena in open light-atom interacting systems by investigating a parametrically amplified quantum Rabi model (QRM) subject to both single- and two-photon decay. In the classical oscillator limit, four composite phases emerge, arising from the possible normal or superradiant regimes across the upper and lower spin branches. A mean-field analysis reveals that the two-photon decay activates the intrinsic nonlinearity of the QRM. The synergy of the coherent and dissipative two-photon processes, together with the spin-boson coupling, constitutes an ``inverted" regime where superradiance emerges exclusively at weak coupling. This regime features first- and second-order superradiant DPTs separated by a tricritical point. Utilizing an adiabatic approach and the semi-classical Langevin formalism, we further study the steady-state structure beyond the mean-field level. The universality classes of the DPTs are identified, with the corresponding critical and finite-size scaling exponents derived and a scaling ansatz proposed to describe the critical behavior.

Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph)

arXiv:2603.18188 [quant-ph]

(or arXiv:2603.18188v2 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2603.18188 Focus to learn more arXiv-issued DOI via DataCite

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