William J. Munro

Bell nonlocality is of broad interest not only because of its foundational significance in quantum theory, but also due to its applications in quantum technologies such as device-independent quantum key distribution (DI-QKD) and quantum randomness expansion. However, it is still challenging to obtain large Bell violation for long distance in experiment. In this work, we propose a loophole-free Bell test protocol using continuous-variable (CV) codes and cavity-QED system. We evaluate the performance of this protocol by calculating the CHSH parameter S and the secret key rate (SKR) in DI-QKD scenario. Various experimental imperfections are considered in the numerical calculation to provide insight into the feasibility and reliability of this protocol. Our results show that Bell violations are achievable up to approximately 18 km with a decent entanglement distribution rate and the SKR for DI-QKD can reach near 100 bits/s at 10 km, significantly outperforming the existing protocols. All the elements in this protocol are reachable with current technologies, so we believe this approach using CV codes provides a feasible and promising route towards practical realization of long-distance Bell nonlocality and secure DI-QKD systems.

Quantum random numbers distinguish themselves from others by their intrinsic unpredictability arising from the principles of quantum mechanics. As such they are extremely useful in many scientific and real-world applications with considerable efforts going into their realizations. Most demonstrations focus on high asymptotic generation rates. For this goal, a large number of repeated trials are required to accumulate a significant store of certifiable randomness, resulting in a high latency between the initial request and the delivery of the requested random bits. Here we demonstrate low-latency real-time certifiable quantum randomness generation from measurements on photonic time-bin states. For this, we develop methods to efficiently certify randomness taking into account adversarial imperfections in both the state preparation and the measurement apparatus. Every 0.12 seconds we generate a block of 8192 random bits which are certified against all quantum adversaries with an error bounded by 2^{-64}. Our quantum random number generator is thus well suited for realizing a continuously operating, high-security, and high-speed quantum randomness beacon.