Leggett-type inequalities for testing nonlocal realism in multipartite systems
arXiv:2108.03665
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.
This 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