Continuous-variable quantum key distribution (CV QKD) using optical coherent detectors is practically favorable due to its low implementation cost, flexibility of wavelength division multiplexing, and compatibility with standard coherent communication technologies. However, there exist two major limitations to the reliability of CV QKD: (1) common CV QKD protocols require the transmission of strong reference pulses, which undermines the security and complicates the experiments, and (2) the security analysis and parameter estimation of CV QKD is complicated due to the infinite-dimensional latent Hilbert space.
In this talk, I will introduce a new time-bin-encoding CV QKD protocol that borrows techniques from the discrete-variable regime while maintaining the advantages of coherent detection. With the key encoded into the relative intensity between two optical modes, we bypass the need for global references. Furthermore, we decouple the security analysis of different photon-number components via phase randomization and propose effective privacy estimation for each component using a carefully designed coherent-detection method. Employing the complementarity security framework, we present a security analysis valid against the most general attack, tight in the asymptotic limit, and easily adaptive to the finite-size regime. Simulations manifest that the protocol using multi-photon components increases the key rate by two orders of magnitude compared to the one using only the single-photon component. Meanwhile, the protocol with four-intensity decoy analysis is sufficient to yield tight parameter estimation with a short-distance key-rate performance comparable to the best Bennett-Brassard-1984 implementation using expensive superconducting nanowire single-photon detectors.
The work can be referred to at https://arxiv.org/abs/2309.03789
Xingjian Zhang is now a visiting scholar at the University of Science and Technology of China. He graduated from the Institute for Interdisciplinary Information Sciences (IIIS) at Tsinghua University in 2023 and obtained the PhD degree in physics. Previously, he obtained the CQIQC Fellowship (2023) from the University of Toronto. Xingjian Zhang is mainly dedicated to the theoretical study of quantum cryptography and quantum communication.