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Two correlated photons incident upon two distant interferometers can produce a coincidence rate that depends nonlocally on the sum of the phases of the interferometers. This effect has been observed for the case in which the optical path length between the two interferometers was 102 m. The results of the experiment are in good agreement with the quantum theory predictions and violate a recently derived inequality for semiclassical field theories.
J. D. Franson (Tue,) studied this question.