We present practical GHz-clocked QKD systems, next generation entanglement QKD technologies, and QKD platform to manage the secure keys and to support a variety of applications. We then show the intrinsic limit of QKD, i.e., a key rate bound, and discuss how to realize the provable (information theoretic) security with a larger secrecy capacity over longer distances. In particular, we present a basic theory of physical layer cryptography, which characterizes the secrecy capacity, and engineers the tradeoff between the efficiency of reliable transmission and secrecy of communication. We introduce a concept to unify these schemes in photonic network, referred to as quantum photonic network. Future issues for realizing this new network paradigm are discussed.
We present practical GHz-clocked QKD systems, next generation entanglement QKD technologies, and QKD platform to manage the secure keys and to support a variety of applications. We then show the intrinsic limit of QKD, i.e., a key rate bound, and discuss how to realize the provable (information theoretic) security with a larger secrecy capacity over longer distances. In particular, we present a basic theory of physical layer cryptography, which characterizes the secrecy capacity, and engineers the tradeoff between the efficiency of reliable transmission and secrecy of communication. We introduce a concept to unify these schemes in photonic network, referred to as quantum photonic network. Future issues for realizing this new network paradigm are discussed.
Quantum communication and quantum cryptography are expected to enhance the transmission rate and the security (confidentiality of data transmission), respectively. We study a new scheme which can potentially bridge an intermediate region covered by these two schemes, which is referred to as quantum photonic network. The basic framework is information theoretically secure communications in a free space optical (FSO) wiretap channel, in which an eavesdropper has physically limited access to the main channel between the legitimate sender and receiver. We first review a theoretical framework to quantify the optimal balance of the transmission efficiency and the security level under power constraint and at finite code length. We then present experimental results on channel characterization based on 10 MHz on-off keying transmission in a 7.8 km terrestrial FSO wiretap channel.This article is part of the themed issue 'Quantum technology for the 21st century'.
Abstract High-dimensional quantum key distribution (QKD) based on entangled qudits has emerged as a promising route for advancing the performance and practicality of quantum communication. By extending beyond the qubit framework, qudit entanglement enables the encoding of multiple bits per particle and offers greater robustness against noise, loss, and eavesdropping. In this review, we present qudit-based entanglement QKD protocols and their experimental demonstrations. We first introduce the basic concepts of qudits and provide an overview of foundational qubit-based entanglement QKD schemes, such as Ekert '91 (E91) and Bennett–Brassard–Mermin '92 (BBM92), which establish the core principles of entanglement-based secure key generation. Subsequently, we examine the generalization of these protocols to entangled qudits, highlighting how higher dimensionality enhances secure key rates and noise tolerance. Finally, we survey experimental demonstrations of qudit-based entanglement QKD across photonic platforms and outline prospects, showing that high-dimensional entanglement can be reliably generated, distributed, and measured for QKD with high stability and scalability. Remarkably, these achievements not only verify the feasibility of practical high-dimensional QKD, but also demonstrate clear advantages over qubit-based systems. Overall, theoretical frameworks and experimental realizations reviewed here position photonic qudit-based entanglement QKD as a promising resource for scalable, high-speed, and secure quantum communication networks, unveiling its potential as a central component in the future of quantum information technologies.
Quantum key distribution (QKD) relies on the fundamental principles of quantum mechanics and can theoretically achieve unconditionally secure communication that is provable by information theory. Quantum random number generators, on the other hand, utilize the inherent randomness of quantum phenomena and are capable of generating a truly random entropy source that is unpredictable, unbiased and unrepeatable. These two technologies are crucial for building highly trustworthy and secure communication systems resistant to quantum attacks. However, their large-scale deployment still faces challenges such as system performance optimization, cost control and scale production. Relying on wafer-level fabrication platforms and micro-nanometer processing, integrated photonics technology integrates the core devices of traditional QKD systems (e.g., light source, modulator, and detector) in a single chip at high density. It significantly improves the miniaturization, operational stability and cost-effectiveness of the system, and enhances the intrinsic security, and becomes a key enabling platform to drive QKD and QRNG from laboratory to engineering applications. In this paper, we systematically review the recent breakthroughs of photonic integrated QKD based on different material platforms (SOI/InP/TFLN/Si3N4) in terms of core metrics, such as transmission distance and key rate, as well as the significant breakthroughs of integrated QRNG in terms of random number generation rate and system integration. Finally, the future development direction of this field is discussed and outlooked from the four dimensions of practical security of QKD systems, on-chip implementation of cutting-edge QKD protocols, practical fully-integrated QKD systems, and synergistic optimization of high performance and high integration of integrated QRNG.
By leveraging the fundamental principles of quantum mechanics, quantum cryptography represents a paradigm shift in secure communication by providing information-theoretic security, where any eavesdropping attempt can be intrinsically detected, and by offering resistance to computational attacks, including those posed by future quantum computers that threaten classical cryptographic schemes. To establish Quantum Key Distribution (QKD) as a significant tool in cybersecurity, this study examines the foundational principles of quantum cryptography, focusing on quantum algorithms, quantum bits, and quantum gates. We examine the fundamental QKD protocols and conduct a comparative study of prominent QKD protocols, including BB84, B92, E91, B92, SARG04, COW, Continuous Variable, Six State, Device Independent, and advanced protocols such as MDI-QKD and Twin-Field QKD, to evaluate key rate, distance, and security parameters. A systematic review of the literature has been conducted on the evolution of QKD protocols and networks, QKD integration with advanced technologies like blockchain, IoT, and machine learning, and the practical deployment of quantum communication is studied in this paper. The integration of AI and ML into QKD systems is investigated to explain future algorithm development and performance improvements. Also the function of QKD in quantum networks and the Internet of Things (IoT) is assessed. This paper further delves into the operation of quantum networks, detailing the roles of quantum relays, routers, repeaters, and Free Space Optics (FSO) in enhancing the efficiency and scalability of QKD. Assessing simulators such as SimulaQron, Qiskit, QuNetSim, and QKDNetSim, offering a perception into experimental implementation and protocol validation, resolves the difficulties in quantum-secured communication systems. At last, some security threats are discussed, including Laser damage, Trojan horse attacks, photon-number splitting, and detector blinding, for mitigation of risk strategies. Overall, this work contributes to the importance of QKD and quantum networks in shaping the future of secure wireless communication.
Quantum cryptography uses quantum mechanical principles to provide a new level of security to communication networks. This paper describes an advanced system that will provide scalable, cost-effective quantum key distribution (QKD) through the incorporation of quantum and classical infrastructure in a resilient system that will increase data security. The current distance, device vulnerablity and interoperability problems are solved with our proposed model, which supports the usage of entanglement-based repeaters, AI algorithms to manage the keys and MDI-QKD protocols. Owing to its strong resistance to environmental noise and practical attacks, the scheme is suitable for deployment under practical communication environments. Both the experimental verification and the theoretical modeling show a clear enhancement both in security and transmission distance.
Quantum Key Distribution (QKD) offers a revolutionary method for achieving information-theoretic security in communication systems by leveraging quantum mechanical principles. With foundational protocols like BB84 and newer innovations such as phase-matching and device-independent QKD, the field has rapidly progressed from theoretical constructs to real-world prototypes. Recent advancements in integrated photonics, high-speed key generation, and satellite-based systems suggest a transformative potential for global cybersecurity infrastructure. However, significant challenges remain in extending secure communication distances, ensuring practical implementation security, reducing cost and size of components, and integrating QKD into existing network architectures. This paper reviews the state-of-the-art in QKD, discusses emerging trends such as chip-based and layered QKD systems, evaluates satellite and free-space deployments, and examines the practical limitations and solutions for long-distance and high-rate secure communications. It concludes by highlighting future directions including standardization, hybrid classical-quantum infrastructures, and software-defined QKD networks.