Light Statistics from Large Ensembles of Independent Two-level Emitters: Classical or Non-classical?

TL;DR

This paper studies the photon statistics of large ensembles of independent two-level atoms under weak driving, revealing non-classical emission features like antibunching and superbunching influenced by disorder and excitation number.

Contribution

It derives the second-order autocorrelation function for such ensembles, highlighting the transition between classical-like and quantum photon statistics based on scattering mechanisms.

Findings

Observation of strong antibunching and superbunching in photon correlations.

Disorder enhances non-classical emission features.

Photon statistics depend on whether scattering is coherent or spontaneous.

Abstract

We investigate the photon statistics of an ensemble of coherently driven non-interacting two-level atoms in the weak driving regime. As it turns out, the system displays unique emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles. By deriving the second-order autocorrelation function, we show that extraordinary two-photon correlations are obtained, ranging from strong antibunching to superbunching. These features are enhanced by disorder in the emitter positions, and the control parameter is the number of excitations in the system. We observe the appearance of bunching and antibunching when the light is scattered by the atoms predominantly coherently, i.e., mimicking classical Rayleigh scattering, whereas thermal photon statistics is obtained when the light is scattered via spontaneous decay, a well-known quantum effect. The underlying mechanism is the interplay between coherent scattering, which exhibits spatial fluctuations due to interference, and dissipation in the form of isotropic spontaneous decay.