We develop a method to connect the infinite-dimensional description of optical continuous-variable quantum key distribution (QKD) protocols to a finite-dimensional formulation. The secure key rates of the optical QKD protocols can then be evaluated using recently-developed reliable numerical methods for key rate calculations. We apply this method to obtain asymptotic key rates for discrete-modulated continuous-variable QKD protocols, which are of practical significance due to their experimental simplicity and potential for large-scale deployment in quantum-secured networks. Importantly, our security proof does not require the photon-number cutoff assumption relied upon in previous works. We also demonstrate that our method can provide practical advantages over the flag-state squasher when applied to discrete-variable protocols.
@article{arxiv.2101.05799,
title = {Dimension Reduction in Quantum Key Distribution for Continuous- and Discrete-Variable Protocols},
author = {Twesh Upadhyaya and Thomas van Himbeeck and Jie Lin and Norbert Lütkenhaus},
journal= {arXiv preprint arXiv:2101.05799},
year = {2021}
}