Weak entanglement improves quantum communication using only product measurements

TL;DR

This paper demonstrates that weakly entangled states, measured with simple product measurements, can enhance quantum communication tasks like secret sharing, even in noisy or unsteerable states, challenging the notion that strong entanglement is necessary.

Contribution

The study shows that weak entanglement combined with product measurements can outperform classical protocols in quantum communication, including in noisy and unsteerable states, with experimental validation.

Findings

Weakly entangled states improve secret sharing success rates.

Product measurements can reveal quantum advantages in noisy states.

Experimental results confirm advantages beyond entanglement-unassisted protocols.

Abstract

We show that weakly entangled states can improve communication over a qubit channel using only separate, interference-free, measurements of individual photons. We introduce a communication task corresponding to the cryptographic primitive known as secret sharing and show that all steerable two-qubit isotropic states provide a quantum advantage in the success rate using only product measurements. Furthermore, we show that such measurements can even reveal communication advantages from noisy partially entangled states that admit no quantum steering. We then go further and consider a stochastic variant of secret sharing based on more sophisticated, yet standard, partial Bell state analysers, and show that this reveals advantages also for a range of unsteerable isotropic states. By preparing polarisation qubits in unsteerable states, we experimentally demonstrate improved success rates of both secret sharing tasks beyond the best entanglement-unassisted qubit protocol. Our results reveal the capability of simple and scalable measurements in entanglement-assisted quantum communication to overcome large amounts of noise.