Experimental Tests of Bell’s Inequalities with Pairs of Low Energy Correlated Photons
Early in the development of quantum mechanics1, the following question was raised: is it possible (is it necessary) to understand the probabilistic nature of the predictions of quantum mechanics by invoking a more precise description of the world, at a deeper level ? Such a description would complete quantum mechanics, like statistical mechanics complete thermodynamics by invoking the motions of the molecules. Reasoning on a Gedanken-experiment, Einstein Podolsky and Rosen2 concluded to the necessity of completing quantum mechanics. On the other hand, Bohr disagreed with this conclusion3, and one could think that the commitment to either position was only a matter of taste or of philosophical position. This situation changed dramatically when John Bell4 discovered that the two points of view lead to different predictions for the Bohm’s version5 of the E.P.R. Gedanken-experiment. Bell’s paper opened a route towards real experiments. The closest realization of that Gedanken-experiment uses pairs of low energy photons correlated in polarization, as suggested in the late sixties by Clauser, Home, Shimony and Holt6. The second part of this paper will be devoted to the description of these experiments.
KeywordsQuantum Mechanics Supplementary Parameter Coincidence Counting Coincidence Rate Joint Detection
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