Xiao Gong

Given that most implementations of quantum cryptography systems require low light operations for security reasons, limiting the energy of incoming/outgoing optical signals is a central task. In this submission, we propose and demonstrate a novel and practical power limiter using the thermo-optical defocusing effect of an acrylic prism. The results show that a power limiting in the regime of mW or lower can be achieved, and at the same time possess desirable features like compactness, robustness, polarization and spectrum dimension independence, etc. Our work provides an effective way for limiting the incoming/outgoing optical energy, which is important for practical quantum cryptographic protocols. We believe it will attract much interest and possess the potential to become a standard tool for practical quantum applications.

The power of quantum random number generation is more than just the ability to create truly random numbers. It can also enable self-testing, which allows the user to verify the implementation integrity of critical quantum components with minimal assumptions. In this work, we develop and implement a self-testing quantum random number generator (QRNG) chipset capable of generating 15.33 Mbits of certifiable randomness in each run, producing an expansion rate of 5.11×10-4 at a repetition rate of 10 MHz. The chip design is based on a highly loss-and-noise tolerant measurement-device-independent protocol, where random coherent states encoded using quadrature phase shift keying (QPSK) are used to self-test the quantum homodyne detection unit, well-known to be challenging to characterise in practice. Importantly, this proposal opens up the possibility to implement miniaturised self-testing QRNG devices at production scale using standard silicon photonics foundry platforms.

Characterizing the single-photon detection efficiency (SPDE) of a single-photon detector (SPD) is an essential but nontrivial task for various applications. Conventional methods require detailed detector models to calculate the estimated SPDE, which are not always available. In this work, a generalized method based on decoy-state for accurate characterization of SPDs is proposed and experimentally demonstrated. This work provides a new toolbox for rigorous SPD characterization with relaxed assumptions on the detector model, opening new possibilities in device calibration standards and quantum information applications.