Experimental Implementation of Four-User Downstream Access Network Continuous-Variable Quantum Key Distribution

Nowadays, network speeds are increasing rapidly and network security is a growing concern. Quantum key distribution (QKD) can provide unconditionally secure keys at the physical layer for communication networks. The implementation of high-speed QKD quantum networks is important for the security of modern high-speed networks. Here, for the first time, we realized a four-user high-speed 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 attenuations of 4.4 dB, 4.2 dB, 5.6 dB, and 5.8 dB, respectively. In addition, we find that the block size, the number of users, and the channel attenuation have a significant impact on the system performance in real systems. When the block size is
$10^{8}$
and the number of user nodes is four, the maximum channel attenuation that can be supported is about 6 dB. 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.