Ming-Han Li

Quantum key distribution (QKD) has been proven to be an essential technology to resist the threat of quantum computing. Major technological powers such as the United States and countries in Europe have already begun the development of quantum key distribution networks. After years of technological research, China has further developed the operational-level 10,000-kilometre quantum secure communication network for business applications ‘China Quantum Communication Network’ (CN-QCN), developed based on ‘Shanghai-Beijing Backbone’. This report summarizes the advanced practices of CN-QCN in areas such as Backbone and Metropolitan networks organization and network management. It also highlights several initiatives designed to enhance the network usability, proposes a method for evaluating the availability of quantum networks.

The ability to produce random numbers that are unknown to any outside party is crucial for many applications. Device-independent randomness generation (DIRNG) allows new randomness to be provably generated, without needing to trust the devices used for the protocol. This provides strong guarantees about the security of the output, but comes at the price of requiring the violation of a Bell inequality to implement. A further challenge is to make the bounds in the security proofs tight enough to allow expansion with contemporary technology. Thus, while randomness has been generated in recent experiments, the amount of randomness consumed in doing so has been too high to certify expansion based on existing theory. Here we present an experiment that demonstrates device-independent randomness expansion (DIRNE), i.e., where the generated randomness surpasses that consumed. By developing a loophole-free Bell test setup with a single photon detection efficiency of around 81% and exploiting a spot-checking protocol, we achieve a net gain of 2.63 × 10^8 certified bits with soundness error 5.74×10^{−8}. The experiment ran for 220 hours corresponding to an average rate of randomness generation of 8202 bits/s. By developing the Entropy Accumulation Theorem (EAT), we established security against quantum adversaries. We anticipate that this work will lead to further improvements that push device-independence towards commercial viability.