How can entangled quantum probes learn about the entanglement present in matter?*

Scattering techniques have been routinely used to study the structural and dynamic properties of matter. So far, no probe has exploited the characteristic trait of quantum mechanics, namely entanglement. We argue that when a probe is entangled in its different degrees of freedom (for example, trajectory, momentum, energy, orbital angular momentum, and spin), one can observe new phenomena not present in conventional unentangled probes. We derived a general theory for a probe that is entangled in its trajectory and spin degrees of freedom; we applied the theory to the case of entangled neutron scattering from magnetic matter. We show that when the probe is entangled, it can directly unveil the presence of entanglement in the target matter. When the latter is maximally entangled the typical Young-like interference pattern that exists otherwise for an unentangled state gets quantum erased [1]. Moreover, we show that this kind of probe can successfully differentiate between different chiral orders in magnetic materials.

[1] New J. Phys. 23, 083022 (2021)

[2] Nat. Commun. 11, 930 (2020)