Field and long-term demonstration of a wide area quantum key distribution network (1409.1568v2)

Abstract: A wide area quantum key distribution (QKD) network deployed on communication infrastructures provided by China Mobile Ltd. is demonstrated. Three cities and two metropolitan area QKD networks were linked up to form the Hefei-Chaohu-Wuhu wide area QKD network with over 150 kilometers coverage area, in which Hefei metropolitan area QKD network was a typical full-mesh core network to offer all-to-all interconnections, and Wuhu metropolitan area QKD network was a representative quantum access network with point-to-multipoint configuration. The whole wide area QKD network ran for more than 5000 hours, from 21 December 2011 to 19 July 2012, and part of the network stopped until last December. To adapt to the complex and volatile field environment, the Faraday-Michelson QKD system with several stability measures was adopted when we designed QKD devices. Through standardized design of QKD devices, resolution of symmetry problem of QKD devices, and seamless switching in dynamic QKD network, we realized the effective integration between point-to-point QKD techniques and networking schemes.

• The paper presents a field demonstration of a wide-area quantum key distribution (QKD) network connecting three cities over 150km using existing fiber infrastructure.
• The network architecture combines mesh and point-to-multipoint designs, addressing challenges like device symmetry and dynamic switching for seamless operation.
• Operating for over 5000 hours, the network proved the long-term reliability and practical viability of QKD systems for secure communication in realistic environmental conditions.

Field and Long-term Demonstration of a Wide Area Quantum Key Distribution Network

The paper presents a comprehensive paper on the design, deployment, and evaluation of a wide area quantum key distribution (QKD) network, namely the Hefei-Chaohu-Wuhu network, extending over more than 150 kilometers. Leveraging the existing communication infrastructure of China Mobile Ltd., this endeavor connects three cities using both metropolitan area QKD networks and intercity QKD links, significantly contributing to the real-world application and understanding of QKD networks.

Network Architecture and Configuration

The Hefei-Chaohu-Wuhu network exemplifies a combination of mesh and access network architectures. The Hefei metropolitan area is configured as a full-mesh core network with five nodes ensuring all-to-all connectivity, advocating robust connectivity and reliability, alongside a demonstrated quantum access network in Wuhu that employs a point-to-multipoint approach.

• Hefei Metropolitan Network: The use of QKD routers and full-mesh optical switches facilitates dynamic routing and inter-nodal connectivity. This setup results in a versatile network capable of adapting to varying communication needs.
• Wuhu Metropolitan Network: Utilizes a simpler point-to-multipoint architecture. This section of the network is crucial for testing the efficacy of QKD infrastructures in serving multiple end-users from a central node.

Challenges and Innovations

One of the notable challenges addressed in this network is maintaining QKD device symmetry to ensure interoperability and seamless communication across various network nodes. The authors achieved this through the development of consistent Faraday-Michelson interferometers, reflected in the low quantum bit error rates (QBER) observed during back-to-back tests, with all values below 1.20%.

Furthermore, the paper discusses the implementation of seamless switching methods to handle dynamic network states. Preemptive and automatic switching modes were implemented, enhancing the network's adaptability and performance consistency.

Long-term Performance and Environmental Adaptations

The network was operational for over 5000 hours, with parts of the network running until December of the subsequent year. This extensive runtime provides valuable data on the long-term stability and reliability of QKD systems in realistic conditions, demonstrating their resilience to environmental factors like noise, weather changes, and physical disturbances.

Key measures like multiplexing of quantum and sync signals in the same fiber were employed to minimize synchronization drift due to environmental variations, reinforcing the network's robustness and operational continuity.

Practical Implications and Future Prospects

The realization of the Hefei-Chaohu-Wuhu network underscores the practical viability of QKD for secure communications over substantial distances using existing telecommunication infrastructures. The proven reliability and adaptability point towards a significant potential for broader deployment in commercial applications.

The advancements in networking schemes and technologies, such as dynamic routing and the integration of seamless switching, herald a move towards more flexible and scalable QKD systems. Future developments may include further enhancing the secure key rates by refining hardware and software, and the exploration of techniques such as measurement-device-independent QKD to bolster security measures.

Conclusion

The implementation and long-term operation of the Hefei-Chaohu-Wuhu network mark a critical step in the evolution of QKD networks. The findings advocate for the practicality of deploying QKD in existing communication systems, providing a solid foundation for future research and development in quantum cryptography and secure communication networks.