Kochen-Specker theorem studied with neutron interferometer

TL;DR

This paper experimentally tests the Kochen-Specker theorem using neutron interferometry, demonstrating quantum contextuality through spin-path entanglement and violation of a related inequality.

Contribution

It provides the first experimental verification of the Kochen-Specker theorem with neutron interferometry using spin-path entanglement.

Findings

Observed violation of the inequality with a value of 2.291 +/- 0.008

Confirms quantum contextuality in a single neutron system

Shows incompatibility of noncontextual hidden variable theories with quantum mechanics

Abstract

The Kochen-Specker theorem theoretically shows evidence of the incompatibility of noncontextual hidden variable theories with quantum mechanics. Quantum contextuality is a more general concept than quantum non-locality which is quite well tested in experiments by using Bell inequalities. Within neutron interferometry we performed an experimental test of the Kochen-Specker theorem with an inequality, which identifies quantum contextuality, by using spin-path entanglement in a single neutron system. Here entanglement is achieved not between different particles, but between degrees of freedom, i.e., between spin and path degree of freedom. Appropriate combinations of the spin analysis and the position of the phase shifter allow an experimental verification of the violation of an inequality of the Kochen-Specker theorem. The observed value of (2.291 +/- 0.008), which is above the threshold of 1, clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden variable theories.