Loss of Antibunching

Antibunching, the tendency of bosonic particles to be emitted apart from each other, is an irrefutable evidence of the quantum character of light. The first experimental observation of photon antibunching, done in the late 1970’s, started a technological race to develop sources of single photons showcasing “perfect” antibunching, namely, sources whose probability to emit two photons within an infinitesimal time window is exactly zero. From a theoretical point of view, such a source is easily envisioned: consider a two-level system which, once has been taken into its excited state, cannot receive another excitation until it has emitted a photon. Therefore, a finite time (related to the time it takes to the two-level system to complete the excitation-relaxation cycle) has to pass before the two-level system emits two photons. However, such a two-level system is always surrounded by an environment, and the light it emits has to be observed in order to be processed or further used for applications. Therefore, a physical object has to perform a measurement on the stream of photons, and such a measurement, for fundamental reasons (e.g., the Heisenberg uncertainty principle applied to time and frequency) spoil the observed correlations between the emitted photons. 

In my paper Loss of Antibunching, I explore the mechanisms that lead to a loss of antibunching. We tackle the problem broadly, and take into account both experimental (such as contamination by noise and the time jitter that originates from the physical detector) as well as fundamental factors (such as the effect of frequency filtering or, analogously, detection with finite bandwidth). Thus, we find that time jitter can only drive correlations towards uncorrelation, whereas frequency filtering can alter their type, namely, turning antibunching into bunching. We use a two-level system as the testbed of our theory, and we find that the Mollow triplet is particularly apt at emitting photons with a large variety of statistics.