Post-Measurement Pairing Quantum Key Distribution with Local Optical Frequency Standard

TL;DR

This paper demonstrates a practical post-measurement pairing quantum key distribution system referencing lasers to an absolute frequency standard, achieving high secure key rates over long distances and overcoming previous bounds, thus enabling efficient multi-user quantum networks.

Contribution

The authors introduce a method referencing each user's laser to an absolute frequency standard, simplifying long-distance QKD and enabling high secure key rates over extensive fiber links.

Findings

Achieved a secure key rate of 15.94 bit/s over 504 km fiber.

Over 100 km fiber, the setup delivers 285.68 kbit/s SKR.

Overcomes the absolute repeaterless bound by 1.28 times.

Abstract

The idea of post-measurement coincidence pairing simplifies substantially long-distance, repeater-like quantum key distribution (QKD) by eliminating the need for tracking the differential phase of the users' lasers. However, optical frequency tracking remains necessary and can become a severe burden in future deployment of multi-node quantum networks. Here, we resolve this problem by referencing each user's laser to an absolute frequency standard and demonstrate a practical post-measurement pairing QKD with excellent long-term stability. We confirm the setup's repeater-like behavior and achieve a finite-size secure key rate (SKR) of 15.94 bit/s over 504 km fiber, which overcomes the absolute repeaterless bound by 1.28 times. Over a fiber length 100 km, the setup delivers an impressive SKR of 285.68 kbit/s. Our work paves the way towards an efficient muti-user quantum network with the local frequency standard.