Understanding entanglement and resolving the measurement problem

Abstract

We summarize a recently proposed resolution of the quantum measurement problem. It stems from an insight into entanglement demonstrated in a 1991 experiment involving photon momenta. This experiment shows that, when two superposed quantum systems A and B are entangled, the resulting "pre-measurement state" is not a paradoxical macroscopic superposition of compound states of the two subsystems; for example, Schrodinger's cat is not "smeared" between dead and alive. It is instead a non-local superposition of correlations between states of the subsystems. In Schrodinger's example, an undecayed nucleus is correlated with a live cat, AND a decayed nucleus is correlated with a dead cat, where "AND" indicates the superposition on. This is exactly what we want. We have misinterpreted "dyads" |A> |B> where "A" and "B" are subsystems of a composite system AB. A> |B> does not mean states |A> and |B> both exist. It means instead |B> exists if and only |A> exists, i.e. |A> and |B> are correlated. It is a fact of nature that such correlations are nonlocally coherent: The degree of correlation between A and B depends on the nonlocal phase angle between the arbitrarily distant subsystems. Such coherent correlations are central to the nonlocal collapse of wave functions.