Security analysis and improvement of source independent quantum random number generators with imperfect devices

• Main Authors: Xing Lin, Shuang Wang, Zhen-Qiang Yin, Guan-Jie Fan-Yuan, Rong Wang, Wei Chen, De-Yong He, Zheng Zhou, Guang-Can Guo, Zheng-Fu Han
• Format: Article
• Language: English
• Published: Nature Publishing Group 2020-12-01
• Series: npj Quantum Information
• Online Access: https://doi.org/10.1038/s41534-020-00331-9

Abstract A quantum random number generator (QRNG) as a genuine source of randomness is essential in many applications, such as number simulation and cryptography. Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored, which will cause security problems, especially in high-speed systems. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement devices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.