Quantum fluctuations and correlations in open quantum Dicke models

TL;DR

This paper investigates quantum and classical correlations near the superradiant phase transition in an open quantum Dicke model, revealing that local dissipation can enhance quantum correlations and induce a nonequilibrium superradiant phase with entanglement.

Contribution

The study introduces a novel approach to quantum fluctuations in open systems, showing local dissipation can enhance correlations and lead to a new nonequilibrium phase.

Findings

Local dissipation enhances collective quantum correlations.

A nonequilibrium superradiant phase with entanglement emerges.

Quantum fluctuations approach reveals dissipation effects beyond Holstein-Primakoff approximation.

Abstract

In the vicinity of ground-state phase transitions quantum correlations can display non-analytic behavior and critical scaling. This signature of emergent collective effects has been widely investigated within a broad range of equilibrium settings. However, under nonequilibrium conditions, as found in open quantum many-body systems, characterizing quantum correlations near phase transitions is challenging. Moreover, the impact of local and collective dissipative processes on quantum correlations is not broadly understood. This is, however, indispensable for the exploitation of quantum effects in technological applications, such as sensing and metrology. Here we consider as a paradigmatic setting the superradiant phase transition of the open quantum Dicke model and characterize quantum and classical correlations across the phase diagram. We develop an approach to quantum fluctuations which allows us to show that local dissipation, which cannot be treated within the commonly employed Holstein-Primakoff approximation, rather unexpectedly leads to an enhancement of collective quantum correlations, and to the emergence of a nonequilibrium superradiant phase in which the bosonic and spin degrees of freedom of the Dicke model are entangled.