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Repairing Bell's Theorem for a Class of Down-Conversion Experiments

Popescu, Sandu; Hardy, Lucien; Zukowski, Marek


Keyword(s):bell inequalities; non-locality; down-conversion; quantum optics

Abstract: A certain class of parametric down-conversion Bell type experiments has the following features. In the idealized perfect situation it is in only 50% of cases that each observer receives a photon; in the other 50% of cases one observer receives both photons of a pair while the other observer receives none. The standard approach is to discard the events of the second type. Only the remaining ones are used as the data input to some Bell inequalities. This raises justified doubts whether such experiments could be ever genuine tests of local realism. We propose to take into account these "unfavourable" cases and to analyze the entire pattern of polarization and localization correlations. This departure from the standard reasoning enables one to show that indeed the experiments are true tests of local realism.

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