On how to Produce Entangled States Violating Bell's Inequalities in   Quantum Theory
  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. 
Apoorva Patel (CTS, IISc, Bangalore, India)