Cooperative Breakdown of the Oscillator Blockade in the Dicke Model

TL;DR

This paper uncovers a new nonstationary phase transition in the dissipative Dicke model, where the harmonic oscillator experiences unlimited heating, revealing a cooperative breakdown of the oscillator blockade.

Contribution

It introduces the concept of a cooperative breakdown phase transition in the dissipative Dicke model and analyzes its mechanism and scaling behavior.

Findings

Identification of a nonstationary phase with unlimited oscillator heating

Derivation of the critical coupling scaling with system size

Discussion of suppression via cooling in trapped ion implementations

Abstract

The Dicke model, which describes the coupling of an ensemble of spins to a harmonic oscillator, is known for its superradiant phase transition, which can both be observed in the ground state in a purely Hamiltonian setting, as well as in the steady state of an open-system Dicke model with dissipation. We demonstrate that, in addition, the dissipative Dicke model can undergo a second phase transition to a nonstationary phase, characterized by unlimited heating of the harmonic oscillator. Identifying the mechanism of the phase transition and deriving the scaling of the critical coupling with the system size we conclude that the novel phase transition can be understood as a cooperative breakdown of the oscillator blockade which otherwise prevents higher excitation of the system. We discuss an implementation with trapped ions and investigate the role of cooling, by which the breakdown can be suppressed.