1301.1673 (Art Hobson)

Implications of bipartite interferometry for the measurement problem    [PDF]

Art Hobson

Nonlocal interferometry, in which two photons are entangled in the "measurement state" (MS) of quantum measurement theory, illuminates the measurement problem. Experiments done in 1990 by Rarity and Tapster and by Mandel's group, in which each photon "measures" the other, probe the effect of a variable phase factor inserted between the two superposed terms of the MS. The results show that, when a bipartite (two-part) system is in the MS, its subsystems are not in superpositions but are instead in collapsed, or mixed, states with each subsystem exhibiting a definite, but unpredictable, outcome. Standard quantum theory (without the collapse postulate) predicts this MS and thus correctly predicts these observations. The experiment confirms that, when a quantum system and a measuring apparatus are entangled in the MS, the state actually detected by an observer of either subsystem is the local or "reduced" state of the subsystem. The global superposition state, which continues evolving unitarily, merely records the nonlocal correlations and does not contradict the definite, non-superposed, outcomes. Thus Schrodinger's cat, for example, is in a non-paradoxical mixture of being alive on trials when the nucleus didn't decay, and dead on trials when the nucleus decayed. This resolves the problem of definite outcomes, with no assistance from human minds, other worlds, hidden variables, the environment, a collapse postulate, collapse mechanisms, or "for all practical purposes" arguments.

View original: http://arxiv.org/abs/1301.1673