An introductory review of the theory of continuous-variable quantum key distribution: Fundamentals, protocols, and security

TL;DR

This paper provides an accessible introduction to continuous-variable quantum key distribution, covering fundamental concepts, protocols, security analysis, and advanced topics to help newcomers understand and engage with this rapidly evolving field.

Contribution

It offers a comprehensive, beginner-friendly overview of CV-QKD theory, including security proofs and protocol equivalences, tailored for researchers new to the field.

Findings

Explains the security framework for CV-QKD against collective attacks.

Details the equivalence between prepare-and-measure and entanglement-based protocols.

Addresses advanced topics like measurement-device-independent CV-QKD.

Abstract

Continuous-variable quantum key distribution (CV-QKD) has emerged as a promising approach for secure quantum communication, offering advantages such as high key generation rates, compatibility with standard telecommunication infrastructure, and potential for integration on photonic chips. This review provides an accessible introduction to the theory of CV-QKD, aimed at researchers entering this rapidly developing field. We focus on fundamental concepts, key protocols, and security analysis essential for understanding CV-QKD systems, with a special emphasis on prepare-and-measure protocols using coherent states under asymptotic security conditions. We explain their equivalence to entanglement-based protocols and detail the security proof framework against collective attacks, encompassing both Gaussian and discrete modulation schemes. We also briefly address more advanced topics, including measurement-device-independent CV-QKD and finite-size security analysis. This work is motivated by Brazil's growing investment in quantum communication technologies. By presenting a clear learning path from basic concepts to advanced topics, this work aims to equip newcomers with the essential tools to engage with current research in CV-QKD, thereby supporting the training of a new generation of researchers in this strategic field.