Photon antibunching

Photon detections as a function of time for a) antibunching (e.g. light emitted from a single atom), b) random (e.g. a coherent state, laser beam), and c) bunching (chaotic light). τ_c is the coherence time (the time scale of photon or intensity fluctuations).

Photon antibunching generally refers to a light field with photons more equally spaced than a coherent laser field,^[1] a signature being a measured two-time correlation suppressed below that of a coherent laser field. More specifically, it can refer to sub-Poissonian photon statistics, that is a photon number distribution for which the variance is less than the mean. A coherent state, as output by a laser far above threshold, has Poissonian statistics yielding random photon spacing; while a thermal light field has super-Poissonian statistics and yields bunched photon spacing. In the thermal (bunched) case, the number of fluctuations is larger than a coherent state; for an antibunched source they are smaller.^[2]

^ Anti-bunching and Entanglement - https://web.archive.org/web/20110615173635/http://www.ucd.ie/speclab/UCDSOPAMS/peoplehtml/quantumoptics2006/lecture5.pdf
^ Paul, H (1982). "Photon antibunching". Reviews of Modern Physics. 54 (4): 1061–1102. Bibcode:1982RvMP...54.1061P. doi:10.1103/RevModPhys.54.1061.

[1] Anti-bunching and Entanglement - https://web.archive.org/web/20110615173635/http://www.ucd.ie/speclab/UCDSOPAMS/peoplehtml/quantumoptics2006/lecture5.pdf

[2] Paul, H (1982). "Photon antibunching". Reviews of Modern Physics. 54 (4): 1061–1102. Bibcode:1982RvMP...54.1061P. doi:10.1103/RevModPhys.54.1061.

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