Einstein-Podolsky-Rosen gedankenexperiment

The motivations for considering supplementary parameters will be found in the analysis of the famous Einstein-Podolsky-Rosen Gedankenexperiment. Introducing a reasonable Locality Condition, one can derive Bell s theorem, which states... 

Quantum mechanics tells us that, before observation is made, both spins share - with equal weight - the states 11> and ].). Before a measurement, the probability of either spin to be found in either state is 50%. However, if one performs a measurement, say, in first spin, the state of the second spin becomes determined, no matter the distance between them For many years, this non-local property of entanglement has been perhaps the most controversial and debated aspect of quantum mechanics, since Einstein, Podolsky and Rosen pointed the problem out in a historical paper published in 1935 [13]. Since the EPR paper, as it became known, many decades were necessary until the discovery of a criterion to decide whether non-locality was a physical reality or just a mathematical property of the quantum formalism. This was a main contribution of John Bell, who in 1964 presented such a criterion [14]. The so-called Bell inequality is a statistical test for quantum nonlocality. However, in 1964 there were no experimental conditions to implement such a test in a real physical system. This came about only in 1982 as a seminal work published by Aspect, Grangier and Roger [15], entitled Experimental realization of Einstein-Podolsky-Rosen-Bohm gedankenexperiment a new violation of Bell s inequalities. This paper is considered - at least for the great majority of physicists - as the work where the nonlocality, inherent to entangled states, is demonstrated to be definitely part of the physical world. 

WHY SUPPLEMENTARY PARAMETERS THE EINSTEIN-PODOLSKY-ROSEN-BOHM GEDANKENEXPERIMENT... 

Fig. 1. Einstein-Podolsky-Rosen-Bohm Gedankenexperiment with photons. The two photons V. and V2, emitted in the state (1), are analyzed by linear polarizers in orientations a and One can measure the probabilities of single or joint detections after the polarizers.

A. Aspect, P. Grangier and G. Roger, Experimental Realization of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment A New Violation of Bell s Inequalities, Phys. Rev. Lett. 49 91 (1982). 

The polarization correlation in two-photon processes has thus proved a topic of considerable interest in its own right. However, without doubt, the main stimulus to the performance of polarization correlation measurements came first from the Gedankenexperiment of Bohm and the paper of Bohm and Aharonov in which the so-called paradox of Einstein, Podolsky, and Rosen (EPR) was put in terms of the polarization of photons and subsequently from the work of Bell and its interpretation in experimental terms by Clauser, Home, Shimony, and Holt, and Clauser and Home. ... 

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