Measurement-Protected Quantum Key Distribution

TL;DR

This paper introduces a measurement-protected quantum key distribution method that maintains optimal measurement settings during transmission, enhancing security and robustness against channel noise without requiring channel verification.

Contribution

It proposes a novel measurement protection scheme using local unitaries that preserves measurement optimality and improves security bounds in quantum key distribution.

Findings

Experimental demonstration with photonic qubits confirms effectiveness.

Security bounds are improved, tolerating errors up to 20.7%.

Measurement remains optimal despite channel interactions.

Abstract

In the distribution of quantum states over a long distance, not only are quantum states corrupted by interactions with an environment but also a measurement setting should be re-aligned such that detection events can be ensured for the resulting states. In this work, we present measurement-protected quantum key distribution where a measurement is protected against the interactions quantum states experience during the transmission, without the verification of a channel. As a result, a receiver does not have to revise the measurement that has been prepared in a noiseless scenario since it would remain ever optimal. The measurement protection is achieved by applications of local unitary transformations before and after the transmission, that leads to a supermap transforming an arbitrary channel to a depolarization one. An experimental demonstration is presented with the polarization encoding on photonic qubits. It is shown that the security bounds for prepare-and-measure protocols can be improved, for instance, errors up to 20.7% can be tolerated in the Bennett-Brassard 1984 protocol.