Operational interpretation of coherence in quantum key distribution

TL;DR

This paper establishes a framework linking quantum coherence to the security and key rate of quantum key distribution protocols, providing new insights and improved bounds for practical scenarios.

Contribution

It introduces a coherence-based framework that connects quantum coherence measures to QKD security, deriving new key rate formulas for BB84 and six-state protocols.

Findings

Key rate can be quantified by coherence of shared states

Derived improved key rates for BB84 and six-state protocols

Applied framework to detection efficiency mismatch, improving results

Abstract

Quantum coherence was recently formalized as a physical resource to measure the strength of superposition. Based on the resource theory, we present a systematic framework that connects a coherence measure to the security of quantum key distribution. By considering a generic entanglement-based key distribution protocol under the collective attack scenario, we show that the key rate can be quantified by the coherence of the shared bipartite states. This framework allows us to derive the key rate of the BB84 and six-state protocols. By utilizing fine-grained parameters, we also derive the improved key rates of both protocols within the coherence-based framework. Furthermore, we apply it to a practical issue, detection efficiency mismatch, and obtain an improved result. In conclusion, this framework demonstrates the interplay among coherence, entanglement, and quantum key distribution at a fundamental level.