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.
Highlights
Advancing the frontiers of science often requires the creation of new physical methods to uncover the underlying microscopic mechanisms that give rise to exotic macroscopic phenomena
We show that the mode 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
As the beam coherence length must satisfy βt t, we know that the following data were obtained in the overlap regime: ξ < βt t
Summary
Advancing the frontiers of science often requires the creation of new physical methods to uncover the underlying microscopic mechanisms that give rise to exotic macroscopic phenomena. A myriad of scattering techniques, based on photon, electron, x-ray, or neutron probes, is currently being used with great success to discover and characterize the fundamental properties of complex materials. These probe techniques base their success on the control and manipulation of two of the defining traits of quantum mechanics, namely, the discreteness of elementary physical properties and interference phenomena, allowing inference of certain spacetime correlations of the target sample. Often this entanglement is thought to be at the root of the underlying microscopic mechanisms that give rise to remarkable phenomena such as emergent chirality in spin liquids, topological quantum order, strange metallic behavior, and unconventional superconductivity. A new type of probe that exploits entanglement, a uniquely quantum resource, may help directly reveal some of these phenomena
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