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.
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.
Abstract Quantum key distribution (QKD) represents a cornerstone of secure communication in the quantum era. While discrete-variable QKD (DV-QKD) protocols were historically the first to demonstrate secure key exchange, continuous-variable QKD (CV-QKD) has emerged as a more practical alternative due to its seamless compatibility with current telecommunications infrastructure. CV-QKD relies on coherent and squeezed states of light, offering significant advantages for integration into modern optical networks. This review comprehensively explores the theoretical underpinnings, technological advancements, and practical challenges of CV-QKD. Special attention is given to the role of photonic integrated circuits (PICs) in enabling scalable and efficient implementation of CV-QKD systems. Furthermore, recent advances in machine learning have been leveraged to optimize CV-QKD performance, with data-driven techniques enhancing noise estimation, parameter optimization, and system security. Additionally, tensor networks provide efficient computational tools for analyzing complex quantum correlations, improving the efficiency and robustness of quantum key distribution protocols. These developments, combined with ongoing improvements in quantum photonic integration, pave the way for the practical deployment of large-scale, high-speed quantum-secure networks.
Quantum key distribution (QKD) enables secure secret key exchange with information-theoretic security by leveraging the principles of quantum mechanics. Continuous-variable QKD (CV-QKD), which utilizes coherent states and coherent detection, has gained attention as a promising approach due to its seamless integration with existing telecommunications networks. CV-QKD systems, which are built with standard telecommunication components, open the door—through photonic integration technology—to the development of devices that are more affordable, compact, and energy efficient. This paper reviews the current state of the art and highlights our recent progress toward fully integrated CV-QKD systems.
Continuous Variable Quantum Key Distribution (CV-QKD) is currently experiencing rapid and significant growth. This can be attributed to its capacity to increase resilience to noise and its ease of integration into current optical communication networks. In this article, we review and survey existing work on CV-QKD post-processing techniques, privacy amplification, and key reconciliation. We also classify protocols based on transmission, preparation, and measurement, which allows for a more systematic and organized understanding of protocols, as well as identifying potential vulnerabilities or weaknesses in each component and allowing for targeted improvements to enhance the overall security and efficiency of protocols. Finally, we outline potential research directions and future challenges that require attention to advance the optimization of CV-QKD technology.
Quantum Key Distribution (QKD) protocols offer a revolutionary approach to secure communication, leveraging the principles of quantum mechanics to enable theoretically unbreakable encryption. This comprehensive review examines the security and efficiency of various QKD protocols, including BB84, E91, and Continuous Variable QKD. We analyze the fundamental principles underpinning these protocols, their implementation challenges, and the practical considerations for real-world deployment. Special emphasis is placed on the security proofs of QKD, addressing potential vulnerabilities such as photon number splitting attacks and detector blinding attacks. Additionally, we explore the efficiency of QKD systems in terms of key generation rates, distance limitations, and integration with existing communication infrastructures. Recent advancements in QKD technology, including satellite-based QKD and quantum repeaters, are also discussed. Our findings highlight the critical role of QKD in future-proofing communication security and the ongoing efforts to enhance its practicality and scalability. This review aims to provide a detailed understanding of the current state of QKD protocols, offering insights into their potential to transform secure communications in the quantum era.
This article describes the current technical level of developments in the field of continuous-variable quantum key distribution (CV-QKD). Various classifications are described, the criteria are analyzed, and the optimal protocol is selected. The analysis is focused around device-dependent schemes with a theoretical emphasis, and therefore, a detailed analysis of device-independent CV-QKD and side-channel attacks is out of the scope of the work. However, the latter, one way or another, is taken into account when describing possible classifications. The choice of the optimal protocol was carried out, first of all, from the potential possibility of integration into existing network telecommunication infrastructures. Predominantly, the general classification is carried out in such a way that it is possible to draw up a specific protocol, depending on the task of implementation.
Quantum key distribution allows two parties to establish an encryption key that, by the laws of physics, no other party can have knowledge on and therefore enables information-theoretic communication security. In particular, quantum key distribution with continuous variables (CV-QKD) represents a way to exercise quantum cryptography at a high technological readiness level taking advantage of the leading-edge technological infrastructure provided by the telecom industry. The review by Fabian Laudenbach et al. (article number 1800011) provides a detailed introduction to the mathematical tools and relations required for the security analysis of CV-QKD and particularly deals with the effects of necessarily imperfect hardware components.