Bell's Inequalities and Density Matrices: Revealing “Hidden” Nonlocality

Sandu Popescu
Phys. Rev. Lett. 74, 2619 – Published 3 April 1995
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Abstract

Standard Bell inequalities apply to correlations arising when two or more macroscopically separated systems are each subjected to a single ideal measurement. While these inequalities demonstrate that quantum mechanics and local hidden variable theories yield incompatible predictions for pure states, they fail for mixed states: For mixed states, correlations arising from a single ideal measurement on each system may obey standard Bell inequalities, yet when each system is subjected to a sequence of ideal measurements the correlations are nonlocal. For some situations even this last procedure fails, and we must consider more complex (“nonideal”) measurements.

  • Received 4 April 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.2619

©1995 American Physical Society

Authors & Affiliations

Sandu Popescu

  • Department of Physics, Technion–Israel Institute of Technology, 32000 Haifa, Israel

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Issue

Vol. 74, Iss. 14 — 3 April 1995

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