This experiment duplicates the experiment of Grangier, Roger and Aspect , in which they demonstrate that if a single photon is incident on a beamsplitter, it can only be detected at one of the outputs (not both.) To quote these authors, "a single photon can only be detected once!"
We have simplified the original experiment by implementing it using a parametric downconversion source, as opposed to an atomic beam source. This provides much higher count rates [~100,000 counts-per-second (cps) singles rates and ~8,000 cps coincidence rates.] In the notation of Grangier et al., we measure an anticorrelation parameter a=0.0188 + 0.0067 with a counting time of only 5 minutes. This result violates the classical inequality a>1 by 146 standard deviations, indicating that our field is very well described by a true single-photon state (for which we expect a=0.) In somewhat more standard notation, the parameter a is the same as the degree of second-order coherence: a=g(2)(0).
We have recently extended this work by examining the effects that dead time has on measurements of g(2)(0). We find that dead time can lead to erroneous measured values for g(2)(0). Renormalizing the measurements can correct for such errors, but it is best to use faster electronics with no dead time. For such electronics, see our circuit page.
J. J. Thorn, M. S. Neel, V. W. Donato, G. S. Bergreen, R. E. Davies, and M. Beck, "Observing the quantum behavior of light in an undergraduate laboratory", Am. J. Phys. 72, 1210-1219 (2004).
M. Beck, “Comparing measurements of g(2)(0) performed with different coincidence detection techniques,” J. Opt. Soc. Am. B 24, 2972 – 2978 (2007).
 P. Grangier, G. Roger, and A. Aspect, "Experimental evidence for a photon anticorrelation effect on a beam splitter: A new light on single-photon interferences," Europhys. Lett. 1, 173-179 (1986).
webpage updated 12/20/07
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