Intersubjectivity and value reproducibility of outcomes of quantum measurements

TL;DR

This paper demonstrates that quantum mechanics predicts consistent measurement outcomes across observers and introduces the concept of measurement-induced entanglement, challenging the view that measurement results are merely personal or subjective.

Contribution

It provides a detailed quantum analysis showing that measurement outcomes are reproducible and entangled, refuting the skeptical view of outcomes as personal and highlighting the role of entanglement in measurement.

Findings

Observers measuring the same observable always obtain correlated outcomes.

Measurement induces time-like and space-like entanglement between system and meters.

The conclusions do not extend to generalized or unsharp observables.

Abstract

Every measurement determines a single value as its outcome, and yet quantum mechanics predicts it only probabilistically. The Kochen-Specker theorem and Bell's inequality are often considered to reject a realist view but favor a skeptical view that measuring an observable does not mean ascertaining the value that it has, but producing the outcome, having only a personal meaning. However, precise analysis supporting this view is unknown. Here, we show that a quantum mechanical analysis turns down this view. Supposing that two observers simultaneously measure the same observable, we can well pose the question as to whether they always obtain the same outcome, or whether the probability distributions are the same, but the outcomes are uncorrelated. Contrary to the widespread view in favor of the second, we shall show that quantum mechanics predicts that only the first case occurs. We further show that any measurement establishes a time-like entanglement between the observable to be measured and the meter after the measurement, which causes the space-like entanglement between the meters of different observers. We also show that our conclusion cannot be extended to measurements of so-called 'generalized' or 'unsharp' observables, suggesting a demand for reconsidering the notion of observables in foundations of quantum mechanics.