Objective realism and Joint Measurability in Quantum Many Copies

Abstract

In the standard quantum theory, one can measure precisely only a subset of the incompatible observables. It results in lack of a formal joint probability defining objective realism even if we accept nonlocal or certain faster-than-light interactions. We propose a construction of such realism extending the usual single-copy description to many copies, partially analogous to familiar many worlds. Failure of the standard single copy can be easily looked for experimentally. The copies should interact weakly at the macroscopic level, leading to effective collapse to a single identical pointer state. Experimental evidence for this conjecture could be obtained by detecting incomplete collapse in sequential measurements or finding deviations from the single-copy Born rule when observing simple quantum systems.