Neutron State Entanglement with Overlapping Paths

TL;DR

This paper demonstrates that entangled neutrons maintain their quantum entanglement and contextuality witness values despite significant variations in beam properties, advancing the development of robust neutron-based quantum probes.

Contribution

It shows that neutron entanglement persists under various experimental conditions, supporting the feasibility of entangled neutron scattering as a reliable quantum measurement technique.

Findings

Entanglement persists despite changes in entanglement length and neutron energy.

Contextuality witness remains above Tsirelson bound under varied conditions.

Paths can be distinguishable even when separated by less than the coherence length.

Abstract

The development of direct probes of entanglement is integral to the rapidly expanding field of complex quantum materials. Here we test the robustness of entangled neutrons as a quantum probe by measuring the Clauser-Horne-Shimony-Holt contextuality witness while varying the beam properties. Specifically, we prove that the entanglement of the spin and path subsystems of individual neutrons prepared in two different experiments using two different apparatuses persists even after varying the entanglement length, coherence length, and neutron energy difference of the paths. The two independent apparatuses acting as entangler-disentangler pairs are static-field magnetic Wollaston prisms and resonance-field radio frequency flippers. Our results show that the spatial and energy properties of the neutron beam may be significantly altered without reducing the contextuality witness value below the Tsirelson bound, meaning that maximum entanglement is preserved. We also show that two paths may be considered distinguishable even when separated by less than the neutron coherence length. This work is the key step in the realization of the new modular, robust technique of entangled neutron scattering.