Intractability of Witnessing Entangled Measurements Device Independently

TL;DR

This paper demonstrates that in device-independent scenarios, entangled measurements can be simulated without entanglement, challenging the assumption that entangled measurements are necessary to replicate certain quantum behaviors.

Contribution

It shows that entanglement can be transferred from measurements to states, indicating no black-box measurement scenario necessarily requires entangled measurements.

Findings

Entangled measurements can be simulated without entanglement.

No black-box measurement scenario inherently requires entangled measurements.

Implications for understanding and witnessing entanglement in quantum systems.

Abstract

Protocols have been previously proposed to certify the presence of an entangled measurement in a fully device-independent manner. Here, I provide models for these protocols in which the claimed measurement is not entangled, and demonstrate it is always possible to displace entanglement from measurements to measured states for a general class of device-independent scenarios. This indicates that no black-box measurement scenario requires entangled measurements to replicate its behavior, which is relevant to our fundamental understanding of this phenomenon and how to witness it.