Nonclassical Radiation from Thermal Cavities in the Ultrastrong Coupling Regime

TL;DR

This paper investigates how thermal cavities in the ultrastrong coupling regime exhibit nonclassical photon statistics, with correlation functions deviating from classical thermal light behavior, depending on temperature and coupling strength.

Contribution

It reveals that thermal photons in ultrastrong coupling can show nonclassical correlations, contrasting with traditional thermal light.

Findings

Photon correlation functions vary significantly with temperature and coupling strength.

Thermal photons can exhibit sub-Poissonian or super-Poissonian statistics.

Nonclassical photon statistics emerge in the ultrastrong coupling regime.

Abstract

Thermal or chaotic light sources emit radiation characterized by a slightly enhanced probability of emitting photons in bunches, described by a zero-delay second-order correlation function $g^{(2)}(0) = 2$. Here we explore photon-coincidence counting statistics of thermal cavities in the ultrastrong coupling regime, where the atom-cavity coupling rate becomes comparable to the cavity resonance frequency. We find that, depending on the system temperature and coupling rate, thermal photons escaping the cavity can display very different statistical behaviors, characterised by second-order correlation functions approaching zero or greatly exceeding two.