  Feynman's path integrals provide a hidden variable description of quantum
mechanics (and quantum field theories). The time evolution kernel is unitary in
Minkowski time, but generically it becomes real and non-negative in Euclidean
time. It follows that the entangled state correlations, that violate Bell's
inequalities in Minkowski time, obey the inequalities in Euclidean time. This
observation emphasises the link between violation of Bell's inequalities in
quantum mechanics and unitarity of the theory. Search for an evolution kernel
that cannot be conveniently made non-negative leads to effective interactions
that violate time reversal invariance. Interactions giving rise to geometric
phases in the effective description of the theory, such as the anomalous
Wess-Zumino interactions, have this feature. I infer that they must be present
in any set-up that produces entangled states violating Bell's inequalities.
Such interactions would be a crucial ingredient in a quantum computer.

Quantum Physics;High Energy Physics - Theory