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Phys. Rev. A 49, 4331–4338 (1994)

Causality constraints on nonlocal quantum measurements

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Sandu Popescu
Service de Physique Théorique, Université Libre de Bruxelles, Campus Plaine CP 225, Boulevard du Triomphe, 1050 Bruxelles, Belgium

Lev Vaidman
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel-Aviv, 69978 Israel

Received 2 April 1993; published in the issue dated June 1994

Consequences of relativistic causality for measurements of nonlocal characteristics of composite quantum systems are investigated. It is proved that verification measurements of entangled states necessarily erase local information. A complete analysis of measurability of nondegenerate spin operators of a system of two spin-1/2 particles is presented. It is shown that measurability of certain projection operators which play an important role in axiomatic quantum theory contradicts the causality principle.

© 1994 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevA.49.4331
DOI:
10.1103/PhysRevA.49.4331
PACS:
03.65.Bz