Coherent state photon sources are widely used in quantum information processing. In many applications, such as quantum key distribution (QKD), a coherent state is functioned as a mixture of Fock states by assuming its phase is continuously randomized. In practice, such a crucial assumption is often not satisfied and, therefore, the security of existing QKD experiments is not guaranteed. To bridge this gap, we provide a rigorous security proof of QKD with discrete-phase-randomized coherent state sources. Our results show that the performance of the discrete-phase randomization case is close to its continuous counterpart with only a small number (say, 10) of discrete phases. Comparing to the conventional continuous phase randomization case, where an infinite amount of random bits are required, our result shows that only a small amount (say, 4 bits) of randomness is needed.
@article{arxiv.1410.3217,
title = {Discrete-phase-randomized coherent state source and its application in quantum key distribution},
author = {Zhu Cao and Zhen Zhang and Hoi-Kwong Lo and Xiongfeng Ma},
journal= {arXiv preprint arXiv:1410.3217},
year = {2015}
}