Quantum key distribution (QKD) enables secure key exchanges between two remote users. The ultimate goal of secure communication is to establish a global quantum network. The existing field tests suggest that quantum networks are feasible. To achieve a practical quantum network, we need to overcome several challenges including realizing versatile topologies for large scales, simple network maintenance, extendable configuration and robustness to node failures. To this end, we present a field operation of a quantum metropolitan-area network with 46 nodes and show that all these challenges can be overcome with cutting-edge quantum technologies. In particular, we realize different topological structures and continuously run the network for 31 months, by employing standard equipment for network maintenance with an extendable configuration. We realize QKD pairing and key management with a sophisticated key control centre. In this implementation, the final keys have been used for secure communication such as real-time voice telephone, text messaging and file transmission with one-time pad encryption, which can support 11 pairs of users to make audio calls simultaneously. Combined with intercity quantum backbone and ground–satellite links, our metropolitan implementation paves the way toward a global quantum network.

量子密钥分发 (QKD) 支持两个远程用户之间的安全密钥交换。安全通信的最终目标是建立一个全球量子网络。现有的现场测试表明量子网络是可行的。为了实现一个实用的量子网络，我们需要克服几个挑战，包括实现大规模的通用拓扑、简单的网络维护、可扩展的配置和对节点故障的鲁棒性。为此，我们展示了一个具有 46 个节点的量子城域网的现场操作，并表明所有这些挑战都可以通过尖端的量子技术来克服。特别是我们实现了不同的拓扑结构，并通过采用可扩展配置的网络维护标准设备，实现网络连续运行31个月。我们通过复杂的密钥控制中心实现 QKD 配对和密钥管理。在该实施方案中，最终密钥已用于安全通信，如实时语音电话、短信和文件传输，一次性加密，可支持11对用户同时进行音频通话。结合城际量子主干和地面卫星链路，我们的城市实施为全球量子网络铺平了道路。