Demonstration of quantum correlations that are incompatible with absoluteness of measurement

TL;DR

This paper demonstrates that quantum correlations can violate the assumption of measurement absoluteness, showing that different observer perspectives lead to incompatible probability predictions, challenging classical notions of measurement.

Contribution

It introduces an operational framework to test measurement absoluteness versus non-absoluteness, revealing that quantum correlations can violate the absoluteness assumption in new scenarios.

Findings

Quantum correlations incompatible with measurement absoluteness.

Operational test scenarios distinguish between classical, AoM, and NoM.

Hierarchy of probability sets among classical, AoM, and NoM theories.

Abstract

Exploiting the tension between the two dynamics of quantum theory (QT) in the Wigner's Friend thought experiment, we point out that the standard QT leads to inconsistency in observed probabilities of measurement outcomes between two super-observers - Wigner and his Student. To avoid such inconsistent predictions of QT, we hypothesize two distinct perspectives. The first one is "Absoluteness of measurement (AoM)," that is, any measurement process is an absolute event irrespective of other observers and yields a single outcome. The other is "Non-absoluteness of measurement (NoM)" as the negation of AoM. We introduce an operational approach, first with one friend and then with two spatially separated friends, to test the validity of these two perceptions in quantum theory without assuming the details of the experiment. First, we show that the set of probabilities obtainable for NoM is strictly larger than the set obtainable for AoM. We provide the simplest scenario so far, involving a single quantum preparation and one unitary operation by a super-observer that can demonstrate correlations incompatible with AoM. Remarkably, in the scenario with spatially separated observers, we present a strict hierarchy among the sets of probabilities observed in the following three theories: classical or local realist, quantum theory with AoM, and quantum theory with NoM.