Practical continuous-variable quantum key distribution with composable security

TL;DR

This paper presents a practical continuous-variable quantum key distribution system that achieves composable security with finite resources, marking a significant step towards practical quantum cryptography.

Contribution

It introduces the first CVQKD system capable of generating composable keys with finite coherent states, supported by novel security proofs and stable system design.

Findings

Secure against collective attacks with N ≈ 3.5×10^8 states

Achieved composable security with finite resources

Enhanced system stability and low noise operation

Abstract

A quantum key distribution (QKD) system must fulfill the requirement of universal composability to ensure that any cryptographic application (using the QKD system) is also secure. Furthermore, the theoretical proof responsible for security analysis and key generation should cater to the number $N$ of the distributed quantum states being finite in practice. Continuous-variable (CV) QKD based on coherent states, despite being a suitable candidate for integration in the telecom infrastructure, has so far been unable to demonstrate composability as existing proofs require a rather large $N$ for successful key generation. Here we report the first Gaussian-modulated coherent state CVQKD system that is able to overcome these challenges and can generate composable keys secure against collective attacks with $N \lesssim 3.5\times10^8$ coherent states. With this advance, possible due to novel improvements to the security proof and a fast, yet low-noise and highly stable system operation, CVQKD implementations take a significant step towards their discrete-variable counterparts in practicality, performance, and security.