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 realising 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 realise different topological structures and continuously run the network for 31 months, by employing standard equipment for network maintenance with an extendable configuration. We realise QKD pairing and key management with a sophisticated key control center. 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 inter-city quantum backbone and ground-satellite links, our metropolitan implementation paves the way toward a global quantum network.
Reconfigurable Four-Photon Interference among Three Nodes on a Field Deployed Metropolitan Fiber Network
University of Tennessee, Chattanooga（田纳西大学查塔努加分校）；UTC Quantum Center（UTC量子中心）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）；Texas A&M University（德克萨斯农工大学）
Self-stabilized high-dimensional quantum key distribution on a metropolitan free-space link
Fraunhofer Institute for Applied Optics and Precision Engineering（弗劳恩霍夫应用光学和精密工程研究所）；Friedrich Schiller University, Institute of Applied Physics, Abbe Center of Photonics（弗里德里希·席勒大学应用物理学院阿贝光子学中心）
Entanglement distribution and quantum storage of more than 8000 modes over a metropolitan network
University of Geneva（日内瓦大学）；Aalto University（阿尔托大学）；Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris（巴黎高等化学学院，PSL大学，法国国家科学研究中心，巴黎化学研究 institute）
A Metropolitan-scale Multiplexed Quantum Repeater with Bell Nonlocality
University of Science and Technology of China（中国科学技术大学）；Laboratory of Quantum Information, University of Science and Technology of China（中国科学技术大学量子信息实验室）；Anhui Province Key Laboratory of Quantum Network, University of Science and Technology of China（中国科学技术大学安徽省量子网络重点实验室）；CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学中国科学院量子信息与量子物理前沿卓越中心）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
Ad-hoc hybrid-heterogeneous metropolitan-range quantum key distribution network
Fraunhofer Institute for Applied Optics and Precision Engineering IOF（弗劳恩霍夫应用光学和精密工程研究所）；Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut, HHI（弗劳恩霍夫电信研究所）；Max-Planck Institute for the Science of Light MPL（马克斯·普朗克光科学研究所）；German Aerospace Center DLR（德国航空航天中心）；Institute of Applied Physics, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学应用物理研究所）
A hybrid quantum network linking telecom-wavelength atomic and solid-state nodes
Pritzker School of Molecular Engineering, University of Chicago（芝加哥大学普里茨克分子工程学院）；Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences（奥地利科学院量子光学与量子信息研究所）；Institute for Experimental Physics, University of Innsbruck（因斯布鲁克大学实验物理研究所）；Materials Science Division, Argonne National Laboratory（阿贡国家实验室材料科学部）；Q-NEXT, Argonne National Laboratory（阿贡国家实验室Q-NEXT）
Quantum Networks Using Color Defects in Diamond: Principles, Progress, and Perspectives
Indian Institute of Technology Bombay（印度理工学院孟买分校）；Humboldt-Universität zu Berlin（柏林洪堡大学）；Ferdinand-Braun-Institut (FBH)（费迪南德·布劳恩研究所）；Northwestern University（西北大学）；Center for Photonic Communication and Computing, Department of Electrical and Computer Engineering, Northwestern University（西北大学电气与计算机工程学院光子通信与计算中心）；Center of Excellence for Quantum Information, Computing Science and Technology, Indian Institute of Technology Bombay（印度理工学院孟买分校量子信息、计算科学与技术卓越中心）
InterQnet: A Heterogeneous Full-Stack Approach to Co-designing Scalable Quantum Networks
Argonne National Laboratory（阿贡国家实验室）；Northwestern University（西北大学）；The University of Chicago（芝加哥大学）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；Q-NEXT, Argonne National Laboratory（Q-前沿，阿贡国家实验室）；University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
