Improved finite-size key rates for discrete-modulated continuous variable quantum key distribution under coherent attacks

TL;DR

This paper presents an improved finite-size security proof and key rate calculation for a discrete-modulated CVQKD protocol under coherent attacks, leveraging advanced entropy and optimisation techniques.

Contribution

It introduces a new security proof against coherent attacks in the finite-size regime and demonstrates enhanced key rates using recent optimisation methods.

Findings

Positive key rates achievable at metropolitan distances for around 10^8 rounds

Utilizes the generalised entropy accumulation theorem for security analysis

Employs recent conic optimisation techniques to improve key rate calculations

Abstract

Continuous variable quantum key distribution (CVQKD) with discrete modulation combines advantages of CVQKD, such as the implementability using readily available technologies, with advantages of discrete variable quantum key distribution, such as easier error correction procedures. We consider a prepare-and-measure CVQKD protocol, where Alice chooses from a set of four coherent states and Bob performs a heterodyne measurement, the result of which is discretised in both key and test rounds. We provide a security proof against coherent attacks in the finite-size regime, and compute the achievable key rate. To this end, we employ the generalised entropy accumulation theorem, as well as recent advances in conic optimisation, yielding improved key rates compared to previous works. At metropolitan distances, our method can provide positive key rates for the order of $10^8$ rounds.