Simple security analysis of phase-matching measurement-device-independent quantum key distribution

TL;DR

This paper introduces a simplified, secure variation of phase-matching measurement-device-independent QKD that uses non-phase-randomized states, achieves tight key rates, and can surpass the repeaterless bound with current technology.

Contribution

It proposes a new PM-MDI QKD protocol with reduced sifting cost, provides a simple security proof, and demonstrates the protocol's ability to beat the repeaterless bound under realistic conditions.

Findings

Achieves tight key rates with a simple security proof.

Confirms square root scaling and loss limit in key rate.

Can surpass the repeaterless bound with current technology.

Abstract

Variations of phase-matching measurement-device-independent quantum key distribution (PM-MDI QKD) protocols have been investigated before, but it was recently discovered that this type of protocol (under the name of twin-field QKD) can beat the linear scaling of the repeaterless bound on secret key rate capacity. We propose a variation of PM-MDI QKD protocol, which reduces the sifting cost and uses non-phase-randomized coherent states as test states. We provide a security proof in the infinite key limit. Our proof is conceptually simple and gives tight key rates. We obtain an analytical key rate formula for the loss-only scenario, confirming the square root scaling and also showing the loss limit. We simulate the key rate for realistic imperfections and show that PM-MDI QKD can overcome the repeaterless bound with currently available technology.