Continuing efforts have been made to develop practical quantum key distribution (QKD) systems on the installed fiber networks since early 2000s [1]. Recently, several groups have demonstrated high-speed QKD systems [2,3] with GHz-clock frequency working stably on the installed-fiber networks [4-7]. Along with the hardware development, an efficient key management protocol [7] has been implemented to construct a QKD platform to supply information-theoretically secure key for multiple applications. The highly available QKD platform is expected to promote social deployment of the QKD technology.
Continuing efforts have been made to develop practical quantum key distribution (QKD) systems on the installed fiber networks since early 2000s [1]. Recently, several groups have demonstrated high-speed QKD systems [2,3] with GHz-clock frequency working stably on the installed-fiber networks [4-7]. Along with the hardware development, an efficient key management protocol [7] has been implemented to construct a QKD platform to supply information-theoretically secure key for multiple applications. The highly available QKD platform is expected to promote social deployment of the QKD technology.
In a society based on the continuous exchange of sensitive data and information, the importance of secure and trustful communications is essential. Quantum key distribution (QKD) makes it possible to share data in an unconditionally secure way exploiting the basic principles of Quantum Mechanics [1]. During the last 30 years, many QKD protocols have been developed and tested, achieving long distance transmission [2] and secret key rates up to hundreds of Mbits per second [3]. However, this technology is still far from a large-scale deployment in existing fiber networks and telecom infrastructures, due to multiple factors: low secret-key rate, limited distance between users, lack of applications, high costs and high requirements in terms of low noise fiber links.
The distribution of secret keys with information-theoretic security, made possible by the laws of quantum mechanics, is undoubtedly one of the main achievements of quantum information processing and communications. In recent years, quantum key distribution (QKD) has been implemented in real-world conditions and commercial systems are now available. Despite this progress, however, QKD remains a relatively difficult to operate and costly technology, hindering its widespread use for high-security applications. The photonic integration of QKD devices can play a crucial role in this direction by reducing their size and cost by several orders of magnitude.
Quantum key distribution (QKD) constitutes a symmetric secret key negotiation protocol capable of maintaining information-theoretic security. Given the recent advances in QKD networks, they have evolved from academic research to some preliminary applications. A QKD network consists of two or more QKD nodes interconnected by optical fiber or free space links. The secret keys are negotiated between any pair of QKD nodes, and then they can be delivered to multiple users in various areas for ensuring long-term protection and forward secrecy. We commence by introducing the QKD basics, followed by reviewing the development of QKD networks and their implementation in practice. Subsequently, we describe the general QKD network architecture, its elements, as well as its interfaces and protocols. Next, we provide an in-depth overview of the associated physical layer and network layer solutions, followed by the standardization efforts as well as the application scenarios associated with QKD networks. Finally, we discuss the potential future research directions and provide design guidelines for QKD networks.
The current state, emerging trends, and practical challenges of optical fiber-based power network SCADA quantum communication must be addressed to fully utilize the technological platform's potential in real-world power system SCADA communications involving massive volumes of real-time data, as well as in managing, encoding, and applications such as quantum cryptography. Quantum key distribution (QKD) is an essential part of the cybersecurity paradigm for quantum communication. Even though quantum computing with individual circuits yields probabilistic outcomes for the problem at hand, real-world datasets are complex and challenging to handle, even with telemetry. When using the cybersecurity triad of availability, confidentiality, and integrity (CIA) in reverse order (AIC), availability is given priority in electric power networks. This research assesses the use of the BB84, E91, B92, and SARG04 cryptographic protocols by applying them to large, multivariate power-system SCADA datasets and comparing the outcomes. By leveraging the variety of QKD protocols available with quantum electronics hardware, this simulation work provides a promising avenue for developing implementable frameworks and deploying SCADA/PMU networks in actual power systems.
The threat quantum computers pose to classical public-key cryptography motivates the deployment of quantum-safe communication for critical infrastructure such as healthcare, finance, and energy systems. Quantum key distribution (QKD) and post-quantum cryptography (PQC) offer complementary security guarantees, information-theoretic key exchange and quantum-resistant end-to-end authentication that can be combined in a layered architecture. Here, we demonstrate a field-deployed quantum-secure network integrating entanglement-based QKD with end-to-end PQC over 140 km of installed fiber in Thuringia, Germany, connecting a rural health kiosk to a university hospital via a trusted-node architecture comprising heterogeneous underground and aerial fiber links. Unlike conventional deployments that rely on a dedicated key management system to forward keys to applications, our architecture injects QKD keys directly into standard Linux-based VPN tunnels between adjacent nodes, while PQC secures the communication end-to-end, remaining fully compatible with existing infrastructure and software. Polarization-entangled photon pairs were generated at 810 nm and 1550 nm, with the telecom photon transmitted over deployed fiber. Active polarization stabilization and dispersion compensation preserve the entanglement and enable 22 days of continuous, fully autonomous operation, further underscoring the technological maturity of entanglement-based QKD approaches in a real-world fiber environment. Although the two deployed links were operated during separate rather than concurrent periods, the predominantly aerial link exhibited markedly greater instability, with QBER variations most strongly correlated with wind speed. The generated keys secured a telemedicine proof-of-concept without modifying existing medical systems, demonstrating a practical framework for quantum-safe critical infrastructures.