Future-proofing current fibre networks with quantum key distribution (QKD) is an attractive approach to combat the ever growing breaches of data theft. To succeed, this approach must offer broadband transport of quantum keys, efficient quantum key delivery and seamless user interaction, all within the existing fibre network. However, quantum networks to date either require dark fibres and/or offer bit rates inadequate for serving a large number of users. Here we report a city wide high-speed metropolitan QKD network—the Cambridge quantum network—operating on fibres already populated with high-bandwidth data traffic. We implement a robust key delivery layer to demonstrate essential network operation, as well as enabling encryption of 100 Gigabit per second (Gbps) simultaneous data traffic with rapidly refreshed quantum keys. Network resilience against link disruption is supported by high-QKD link rates and network link redundancy. We reveal that such a metropolitan network can support tens of thousands of users with key rates in excess of 1 kilobit per second (kbps) per user. Our result hence demonstrates a clear path for implementing quantum security in metropolitan fibre networks.

具有量子密钥分发（QKD）的，面向未来的当前光纤网络是一种应对日益增长的数据盗窃行为的有吸引力的方法。为了获得成功，此方法必须在现有光纤网络中提供宽带量子密钥传输，有效的量子密钥传递和无缝的用户交互。然而，迄今为止的量子网络要么需要深色光纤和/或提供的比特率不足以服务于大量用户。在这里，我们报告了一个全市范围的高速城市QKD网络（剑桥量子网络），该网络在已经装有高带宽数据流量的光纤上运行。我们实现了一个强大的密钥传递层，以演示基本的网络操作，并使用快速刷新的量子密钥对100 Gbit / s（Gbps）的同时数据流量进行加密。高QKD链路速率和网络链路冗余支持网络抵御链路中断的弹性。我们揭示了这样一个城域网可以支持数以万计的用户，每个用户的关键速率超过每秒1 kbps（kbps）。因此，我们的结果证明了在城域光纤网络中实施量子安全性的明确途径。