Energy entanglement in neutron interferometry

TL;DR

This paper demonstrates the creation and manipulation of triply entangled states in single neutrons, showing a violation of a Mermin-like inequality that confirms quantum contextuality in a single-particle system.

Contribution

It reports the first experimental realization of triply entangled neutron states and tests quantum contextuality using a Mermin-like inequality.

Findings

Violation of Mermin-like inequality with M=2.558

Demonstration of quantum contextuality in single neutrons

Implementation of GHZ-like entangled states in neutron interferometry

Abstract

Entanglement between degrees of freedom, namely between the spin, path and (total) energy degrees of freedom, for single neutrons is exploited. We implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state and coherently manipulated relative phases of two-level quantum subsystems. An inequality derived by Mermin was applied to analyze the generated GHZ-like state: we determined the four expectation values and finally obtained M=2.558 +/- 0.004 which is clearly above the threshold of 2. This demonstrates the violation of a Mermin-like inequality for triply entangled GHZ-like state in a single-particle system, which, in turn, exhibits a clear inconsistency between noncontextual assumptions and quantum mechanics and confirms quantum contextuality.