Zhenghua Li

Quantum key distribution (QKD) can provide unconditionally secure keys at the physical layer for communication system. In practical environments, communication usually occurs in multi-user and multi-scenario, and point-to-point QKD can no longer meet the modern complex network communication needs. The downstream access network downstream, as an essential component of modern networks, requires QKD technology to ensure its security. Here, we complete a four-user high-speed QKD downstream access network experiment. The repetition frequency of the system is 100 MHz, considering block size of $10^8$, four users achieved secret key rates of 430 kbps, 450 kbps, 150 kbps, and 130 kbps at channel attenuation of 4.4 dB, 4.2 dB, 5.6 dB, and 5.8 dB, respectively. Our experimental results demonstrate the feasibility of multi-user downstream CV-QKD access networks, further advancing the practical application of quantum networks in real-world environments.

Quantum networks provide opportunities and challenges across a range of intellectual and technical frontiers, including quantum computation, communication and others. Unlike traditional communication networks, quantum networks utilize quantum bits rather than classical bits to store and transmit information. As an important part of the networks, the access network can connect multiple end users to the backbone network and provide the so-called last-mile service. In our work, the first four-end-users quantum downstream access network in continuous variable quantum key distribution with a local local oscillator has been experimentally demonstrated. Our results show that each user can get a low level of excess noise and can achieve secret key rate of 546 kbps, 535 kbps, 522.5 kbps and 512.5 kbps under transmission distance of 10 km, respectively with the finite-size block of 1×10⁸. More importantly, the successful demonstration of our quantum downstream access network also paves the way for secure broadband metropolitan and quantum networks.