Leggett-type inequalities for testing nonlocal realism in multipartite systems

Abstract

Nonlocal realism represents the last classical cornerstone in conflict with quantum theory, and has been shown to be largely untenable in bipartite systems [Nature 446, 871 (2007); Nature Physics 4, 681 (2008)]. We extend the Leggett-type nonlocal realistic model to arbitrary N-partite systems with polarizer settings, and derive rigorous inequalities that distinguish quantum predictions from nonlocal realistic theories. The derivation yields a fundamental double inequality that is universally valid, from which the Leggett-type bounds follow under specific measurement settings. As an illustration, we demonstrate quantum violations of these inequalities for Greenberger-Horne-Zeilinger (GHZ) states, with maximal violation 2(\sqrt{5}+1). Our results show that nonlocal realism in multipartite systems is experimentally testable.

arXiv commentThis is a major revision of the previous version (v1). The derivation has been corrected by replacing the min/max bound with a rigorous double inequality, and the supplementary material has been significantly expanded and clarified. All main results, including the GHZ violation 2(\sqrt{5}+1), remain unchanged. 25 pages, 4 figures

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