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

TL;DR

This paper introduces a method to simplify the analysis of optical quantum key distribution protocols by reducing their infinite-dimensional models to finite dimensions, enabling more practical and reliable security assessments.

Contribution

The authors develop a novel approach to connect infinite-dimensional QKD models to finite-dimensional ones, avoiding photon-number cutoff assumptions and improving security proof techniques.

Findings

Allows evaluation of secure key rates using numerical methods

Applies to discrete-modulated continuous-variable protocols

Offers advantages over existing flag-state squasher methods

Abstract

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.