Twin-Field Quantum Key Distribution over 511 km Optical Fiber Linking two Distant Metropolitans

TL;DR

This paper demonstrates a twin-field quantum key distribution over 511 km of optical fiber linking two distant cities, achieving high secure key rates without trusted relays, advancing long-distance quantum communication.

Contribution

It presents the first long-distance twin-field QKD over 511 km fiber without trusted relays, with significantly improved key rates using the SNS protocol.

Findings

Secure key rate is about 1000 times higher than previous systems over the same distance.

Stable single-photon interference achieved over 511 km fiber.

Long-distance QKD without trusted relays is feasible and scalable.

Abstract

The basic principle of quantum mechanics guarantee the unconditional security of quantum key distribution (QKD) at the cost of inability of amplification of quantum state. As a result, despite remarkable progress in worldwide metropolitan QKD networks over the past decades, long haul fiber QKD network without trustful relay has not been achieved yet. Here, through sending-or-not-sending (SNS) protocol, we complete a twin field QKD (TF-QKD) and distribute secure keys without any trusted repeater over a 511 km long haul fiber trunk linking two distant metropolitans. Our secure key rate is around 3 orders of magnitudes greater than what is expected if the previous QKD field test system over the same length were applied. The efficient quantum-state transmission and stable single-photon interference over such a long distance deployed fiber paves the way to large-scale fiber quantum networks.