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Physical Review A

Light statistics from large ensembles of independent two-level emitters: Classical and nonclassical effects

Manuel Bojer, A. Cidrim, P. P. Abrantes, Romain Bachelard, Joachim von Zanthier

Published Oct 20, 2025• 3 citations
Publisher

Abstract

The authors investigate the photon statistics of an ensemble of coherently driven noninteracting two-level atoms in the weakly driven regime. They find emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles, ranging from strong antibunching to superbunching.
DOI
10.1103/5ts6-nlrl

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The statistical properties of fluorescent light from a single two-level atom driven by nonclassical light beams that exhibit antibunching and squeezing are discussed in the weak-field limit. The fields produced in intracavity second-harmonic generation and those produced by superposing the light from a degenerate parametric oscillator with a coherent field are considered to be the models of nonclassical light beams. These fields can be described in terms of real Gaussian random processes with nonzero mean coherent components. Analytical expressions for the fluorescent light intensity, the second-order intensity correlation function, and the variance of the photon number in the steady state are obtained. The effects of driving-field correlations, detuning, and other parameters characterizing the atom-field interaction on the statistics of scattered light are investigated. It is found that for a certain range of parameters the second-order intensity correlation function may vanish at nonzero times. Under certain other circumstances the antibunching of the fluorescent photons is enhanced. These and other interesting features that appear in the scattered light are discussed.
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The quantum statistical behavior of a small collection of N two-state atoms strongly coupled to the field of a high-finessse optical cavity is investigated. Input-output characteristics are recorded over the range 3\ensuremath{\lesssim}N\ensuremath{\lesssim}65, with bistability observed for N\ensuremath{\gtrsim}15 intracavity atoms and for a saturation photon number n0{\mathit{n}}_{0}n0​\ensuremath{\simeq}0.8. For weak excitation the transmitted field exhibits photon antibunching as a nonclassical manifestation of state reduction and quantum interference with the magnitude of the nonclassical effects largely independent of N.
We consider a single two-level atom in an optical cavity, in which the system is driven by a coherent driving field. In the bad-cavity limit, when the cavity loss rate is taken to be large compared to the atomic decay rate and atom-field coupling, the cavity field can be adiabatically eliminated from the equations of motion for the atomic operators. The main effect of the cavity in this limit is the enhancement of spontaneous emission into the cavity mode. For this model, the second-order intensity correlation function g(2)() has been shown to exhibit photon antibunching, sub-Poissonian photon number distributions, and other nonclassical effects.1 In this paper, analytic results are presented for g(2)() for both the transmitted and fluorescent light fields when broadband squeezed light is injected into the cavity. Effects of the squeezing on nonclassical behavior is examined.