Entanglement and the measurement problem

Art Hobson

Published 2020-02-25Version 1

An argument first proposed by John von Neumann shows that measurement of a superposed quantum system creates an entangled "measurement state" (MS) in which macroscopically distinct detector states appear to be superposed, a paradoxical prediction implying the measurement has no definite outcome. We argue that this prediction is based on a misunderstanding of what the MS represents. We show, by studying the phase dependence of entangled photon states generated in parametric down conversion, that the MS represents not a superposition of detector states, but rather a superposition of coherent (i.e. phase-dependent) correlations between detector states and system states. In fact an argument by Einstein shows that a nonlocal entangled state is required, at least briefly, following a quantum system's interaction with a detector. Such a state does not represent a paradoxical macroscopic superposition. This resolves the paradox of indefinite outcomes of measurements.