The Limits of Classical Realism

Jonathan Kirshner

Dipankar Home, A. S. Majumdar

We consider a state of N correlated particles, each with spin j, in which the quantum expectation value of an operator A^ is evaluated. This is found to exceed a bound on A^ obtained from considerations of classical realism. It is indicated from numerical results that this contradiction between quantum mechanics and classical realism persists in the ``strong'' macroscopic limit, i.e., when the values of both N and j are arbitrarily increased. In this argument, the notion of classical realism embodies the twin assumptions of locality (no action at a distance) and noncontextuality (a measurement simply reveals the preexisting value of an observed quantity).

A. J. Leggett

Hyunseok Jeong, Mauro Paternostro, Timothy C. Ralph

We show that failure of local realism can be revealed to observers for whom only extremely-coarse-grained measurements are available. In our instances, Bell's inequality is violated even up to the maximum limit while both the local measurements and the initial local states under scrutiny approach the classical limit. Furthermore, we can observe failure of local realism when an inequality enforced by nonlocal realistic theories is satisfied. This suggests that locality alone may be violated while realism cannot be excluded for specific observables and states. Small-scale experimental demonstration of our examples may be possible in the foreseeable future.

Rudolph Krejci

Justo Pastor Lambare