The Open-System Dicke-Model Quantum Phase Transition with a Sub-Ohmic Bath

TL;DR

This paper investigates how the spectral density of a reservoir influences the critical behavior of a quantum phase transition in an open Dicke model, revealing that sub-Ohmic baths alter the critical exponent.

Contribution

It demonstrates that the critical exponent in an open-system Dicke model depends on the reservoir's spectral density, especially showing changes with sub-Ohmic baths.

Findings

Critical exponent is 1 without spin-bath coupling.

Sub-Ohmic reservoirs reduce the critical exponent below 1.

Reservoir spectral density determines phase transition properties.

Abstract

We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N-spin couple to independent reservoirs at zero temperature. The critical exponent, which is $1$ if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.