The basic principle of quantum mechanics¹ guarantees the unconditional security of quantum key distribution (QKD)^2,3,4,5,6 at the cost of forbidding the amplification of a quantum state. As a result, and despite remarkable progress in worldwide metropolitan QKD networks^7,8 over the past decades, a long-haul fibre QKD network without a trusted relay has not yet been achieved. Here, through the sending-or-not-sending protocol⁹, we achieve twin-field QKD¹⁰ and distribute secure keys without any trusted repeater over a 511 km long-haul fibre trunk that links two distant metropolitan areas. The fibre trunk contains 12 fibres in the cable, three of which are used for the quantum channel, optical synchronization and frequency locking, respectively. The remaining nine are used for classical fibre communication. Our secure key rate is around three orders of magnitude greater than that expected if the previous QKD field-test system was applied over the same length. Efficient quantum-state transmission and stable single-photon interference over such a long-haul deployed fibre pave the way to large-scale fibre quantum networks.

量子力学的基本原理¹以禁止放大量子态为代价保证量子密钥分发 (QKD) ^{2、3、4、5、6}的无条件安全。因此，尽管过去几十年全球城域 QKD 网络^7,8取得了显着进展，但尚未实现没有可信中继的长距离光纤 QKD 网络。在这里，通过发送或不发送协议⁹，我们实现了双场 QKD ¹⁰并在连接两个遥远大都市区的 511 公里长距离光纤干线上分发安全密钥，而无需任何受信任的中继器。光纤主干在光缆中包含 12 根光纤，其中 3 根分别用于量子通道、光同步和频率锁定。其余九个用于经典光纤通信。如果之前的 QKD 现场测试系统在相同长度上应用，我们的安全密钥速率大约比预期的高三个数量级。在如此长距离部署的光纤上的高效量子态传输和稳定的单光子干涉为大规模光纤量子网络铺平了道路。