Perfect discrimination of an orthogonal $2\otimes2$ basis may require collective separable measurements on two copies

Abstract:We consider an orthogonal basis of $\mathbb C^2\otimes\mathbb C^2$ with three entangled states and one product state. This basis is not perfectly distinguishable by LOCC or even by separable measurements when a single copy of the unknown state is available. We show that with two copies no adaptive separable protocol, which measures the copies one at a time, distinguishes the basis perfectly. We then show that a collective separable measurement on the two copies does. Whether two copies suffice for LOCC remains open.

arXiv:2610.16138 [quant-ph]

(or arXiv:2610.16138v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2610.16138 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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