Experimental mode-pairing measurement-device-independent quantum key distribution without global phase-locking

TL;DR

This paper demonstrates a high-performance measurement-device-independent quantum key distribution method that does not require global phase-locking, achieving significant improvements in key rate over long distances using independent lasers.

Contribution

It introduces a mode-pairing approach enabling quantum key distribution without phase-locking between independent lasers, simplifying implementation and enhancing performance.

Findings

Quadratic key-rate improvement over conventional schemes.

Successful long-distance key distribution over 304 km and 407 km fibers.

No need for phase-locking between independent lasers.

Abstract

In the past two decades, quantum key distribution networks based on telecom fibers have been implemented on metropolitan and intercity scales. One of the bottlenecks lies in the exponential decay of the key rate with respect to the transmission distance. Recently proposed schemes mainly focus on achieving longer distances by creating a long-arm single-photon interferometer over two communication parties. Despite their advantageous performance over long communication distances, the requirement of phase-locking between two independent lasers is technically challenging. By adopting the recently-proposed mode-pairing idea, we realize high-performance quantum key distribution without global phase-locking. Using two independent off-the-shelf lasers, we show a quadratic key-rate improvement over the conventional measurement-device-independent schemes in the regime of metropolitan and intercity distances. For longer distances, we also boost the key rate performance by three orders of magnitude via 304 km commercial fiber and 407 km ultra-low-loss fiber. We expect this ready-to-implement high-performance scheme to be widely used in future intercity quantum communication networks.