Contextuality within quantum mechanics manifested in subensemble mean values

TL;DR

This paper demonstrates that in a quantum setup with spin-1/2 particles, subensemble mean values of spin measurements depend on the choice of a compatible path observable, revealing path-spin contextuality at the individual measurement level.

Contribution

It shows that quantum mechanics predicts and explains path-spin contextuality through subensemble mean values in a Mach-Zehnder-type experiment with spin-flippers.

Findings

Subensemble mean values depend on the chosen path observable.

Path-spin contextuality can be inferred at the individual measurement level.

The results support the contextual nature of quantum measurements.

Abstract

For spin-1/2 particles, using a suitable Mach-Zehnder-type setup with a spin-flipper, we argue that it is a direct consequence of the quantum mechanical treatment that an experimentally verifiable \textit{subensemble} mean of the measured values of an arbitrarily chosen spin variable exhibits dependence on the choice of a comeasurable `path' observable. This, in turn, enables inferring path-spin contextuality at the level of individual measured values of spin that are predetermined using a relevant hidden-variable model applied to our setup.