Dimension Reduction in Quantum Key Distribution for Continuous- and Discrete-Variable Protocols

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.