Equilibration and macroscopic quantum fluctuations in the Dicke model

TL;DR

This paper investigates how quantum fluctuations and classical chaos influence the equilibration process in the Dicke model, revealing macroscopic quantum fluctuations through a Fokker-Planck framework.

Contribution

It introduces a Fokker-Planck equation approach to describe quantum dynamics in the Dicke model, linking classical chaos to quantum equilibration and fluctuations.

Findings

Quantum state dynamics obey a Fokker-Planck equation.

Equilibration occurs under classical chaos conditions.

Photon statistics show macroscopic quantum fluctuations.

Abstract

We discuss the unitary quantum dynamics of the Dicke model (spin and oscillator coupled). A suitable quasiprobabilty representing the quantum state turns out to obey a Fokker-Planck equation, with drift terms representing the underlying classical Hamiltonian flow and diffusion terms describing quantum fluctuations. We show (by projecting the dynamics onto a co-moving Poincar\'e section) how the interplay of deterministic drift and quantum diffusion generates equilibration to the microcanonical density, under conditions of global classical chaos. The pertinent photon statistics reveals macroscopic quantum fluctuations.