Constructing practical fully quantum networks within intracity areas

Quantum networks play a pivotal role in the advancement of quantum technologies, expanding the scope of applications and communication distances. However, the absence of practical quantum repeaters poses a significant obstacle to large-scale network construction. Trusted repeater networks, on the other hand, utilize classical trusted repeaters to connect users, thereby sacrificing the information-theoretic security advantage inherent in quantum communication. In this study, we propose a scheme for constructing a fully quantum network in which any two users are directly connected via a switchable optical router, ensuring information-theoretic security across the entire network with existing technologies. Considering that the practical point-to-point quantum communication distance in optical fibers has reached 100 km, our scheme effectively addresses the challenge of building a fully quantum network within an urban area. A 40-km-long functional quantum network has been established using commercial optical links, enabling full operations of tasks such as quantum secure direct communication and quantum key distribution.