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.