Further evidence of nonclassical behavior in optical interference
Z. Y. Ou, L. Mandeļ · Physical Review Letters · 1989
It is demonstrated in a photon coincidence experiment with two photodetectors, in which signal and idler photons produced by parametric down-conversion are allowed to interfere, that the visibility of the interference pattern is well above 50% and remains unchanged when one of the two light beams is attenuated ninefold compared with the other. These results violate classical probability for light waves.