The growth of communication networks and the innovation in technology have driven a rising need for advanced security solutions. With the rise of quantum technologies, traditional communication networks could potentially become vulnerable, posing challenges for academia, research, and industry. Quantum Key Distribution (QKD) has emerged as a promising quantum-safe solution, but its integration into existing infrastructures requires extensive study due to challenges in real-world scenarios. This paper presents an innovative quantum-safe infrastructure deployment and an in-depth analysis of co-propagation, using polarization-entangled QKD in the C-band, coexisting with classical data at 100 Gbps via Dense Wavelength Division Multiplexing (DWDM), and employing production-ready equipment within a real infrastructure. Results validate the coexistence of data and quantum channels within the same fibers, demonstrating the adaptability of traditional networks toward future quantum-safe ecosystems. In addition, the paper provides insights and lessons learned for similar deployments.
The growth of communication networks and the innovation in technology have driven a rising need for advanced security solutions. With the rise of quantum technologies, traditional communication networks could potentially become vulnerable, posing challenges for academia, research, and industry. Quantum Key Distribution (QKD) has emerged as a promising quantum-safe solution, but its integration into existing infrastructures requires extensive study due to challenges in real-world scenarios. This paper presents an innovative quantum-safe infrastructure deployment and an in-depth analysis of co-propagation, using polarization-entangled QKD in the C-band, coexisting with classical data at 100 Gbps via Dense Wavelength Division Multiplexing (DWDM), and employing production-ready equipment within a real infrastructure. Results validate the coexistence of data and quantum channels within the same fibers, demonstrating the adaptability of traditional networks toward future quantum-safe ecosystems. In addition, the paper provides insights and lessons learned for similar deployments.
In an era of unprecedented technological advancement, the rise of quantum computing poses both opportunities and challenges to network security. While quantum computers promise to revolutionize data processing and problem-solving, they also render traditional cryptographic protocols vulnerable, threatening the integrity of current network security systems. Quantum cryptography, particularly quantum key distribution (QKD), emerges as a groundbreaking solution, leveraging the principles of quantum mechanics to ensure unparalleled data security. Unlike classical methods, QKD guarantees secure communication by detecting eavesdropping attempts, as any observation of quantum states disrupts their integrity. This paper explores the pivotal role of quantum cryptography in shaping future network security protocols amidst a landscape of increasing cyber threats. It provides a comprehensive analysis of QKD systems, their integration into existing infrastructure, and their resilience against potential quantum-based attacks. The discussion includes real-world implementations, such as satellite-based QKD networks and fiber-optic quantum communication systems, illustrating their practical viability and scalability. Furthermore, the paper addresses current challenges, including cost, technical complexity, and interoperability with classical networks, offering insights into ongoing research aimed at overcoming these hurdles. As global reliance on digital infrastructure grows, the transition to quantum-resilient security frameworks becomes imperative. Policymakers, industry leaders, and technology developers must collaborate to advance quantum cryptographic technologies and ensure their accessibility. By securing communication channels against both classical and quantum threats, quantum cryptography is positioned to redefine the foundations of network security, paving the way for a more secure and interconnected digital future.
Quantum computing poses a threat to the standard cryptographic primitives and requires the implementation of quantum-safe designs in the existing network infrastructures. Quantum Key Distribution (QKD) has been used to provide information-theoretic security but its compatibility with high capacity wavelength-division multiplexing (WDM) systems is a challenge to its deployment in metropolitan networks. In this paper, the architectural design and outcomes of a field trial assessing the concept of co-propagation of quantum and classical signals in a dense WDM metro environment are introduced. We discuss and measure the performance of multi-span fibres and measure quantum bit error rates in the presence of highlypower classical loading and the stability of the end-to-end key generation. A hybrid architecture that incorporates both QKD and classical post-quantum solutions is introduced to make them more resilient, optimized in terms of spectrum usage, and scalable to operator-grade services. The experimental findings show that QKD can be smoothly incorporated into the metro networks without affecting throughput and latency, indicating a way forward to practical quantum safe communications to future critical infrastructures.
Advances in quantum computing pose a significant threat to the widely used Public Key Infrastructure (PKI). The two leading technologies to address this challenge are Post-Quantum Cryptography and Quantum Key Distribution. A promising approach is the hybridization of these technologies - combining their respective strengths while mitigating their limitations - and integrating them with the cryptographic mechanisms used today to enhance crypto-agility and facilitate transitioning to a quantum-safe infrastructure. However, changing current network protocols to quantum-safe alternatives is not just a matter of security: their efficiency and scalability must also be demonstrated within real-world telecommunications infrastructures to ensure their practical adoption. In this work, we present the first long-running test with detailed measurements of a suite of hybrid quantum-safe protocols that integrate classical cryptography, PQC, and QKD within a production environment (MadQCI). Using standardized protocols and interfaces and employing Transport Layer Security (TLS) as the base protocol for real-world comparison, this study demonstrates the efficiency and scalability of the proposed solution in deployed heterogeneous networks. These results mark a significant step towards the widespread adoption of quantum-safe hybrid protocols and contribute to clarifying the path toward their future standardization in next-generation telecommunications networks.
Quantum networks have been a reality for several years, with quantum key distribution as their primary application. However, several factors still limit their widespread adoption as a user-ready technology. In this work, we present four real-world experiments that demonstrate concrete progress toward the deployment of quantum networks. These field trials showcase the ability to interconnect different countries, interface diverse infrastructures, and exploit quantum properties and innovative technologies to boost key rates and enable coexistence with classical communication channels. Together, they highlight a viable path toward scalable, interoperable, and high-performance quantum-secured communication.
Integrating quantum key distribution (QKD) with classical optical communication is a deployment-friendly and cost-effective approach to advancing QKD network implementation. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of the QKD system, presenting challenges for long-distance coexistence transmission. In this paper, we successfully demonstrate the simultaneous propagation of QKD and optical transport network (OTN) in the C-band over distances exceeding 100 km. We establish a coexistence transmission system based on a commercial OTN equipment and QKD device equipped with the Fabry-Perot filters, demonstrating the feasibility of combining QKD with 11 Tbps (110×100 Gbps) classical data over a 101.86 km fiber. To investigate longer transmission distances, we employ an optimized wavelength allocation method and conduct the co-propagation of QKD and 1 Tbps classical data over a 152.34 km fiber. To the best of our knowledge, these results are the first time that report the integration of QKD and large-capacity classical communication over hundred-kilometer scale fiber. Our works represent a significant advancement in developing OTN networks incorporating QKD systems.
Quantum Key Distribution (QKD) exploits the principles of quantum mechanics to enable information-theoretic security, offering significant advantages over classical cryptographic approaches. Despite extensive experimental demonstrations worldwide, many implementations remain confined to laboratory environments that may be impractical for large-scale deployment. This thesis addresses the critical challenge of making QKD viable within real-world telecommunications networks. Current field trials often prioritise metrics such as distance and key rate at the expense of practicality, employing ultra-low-loss fibres, custom components, and dedicated dark channels. These constraints could hinder integration with existing infrastructure. To overcome these limitations, this work introduces UKQNtel—a testbed designed to incorporate commercial-grade equipment and multiplex quantum and classical traffic. UKQNtel represents the first field trial of a coherent one-way QKD system integrated with a commercial-grade encrypted Dense Wavelength Division Multiplexing (DWDM) network, delivering 500 Gbps of encrypted data over 121 km of real-world fibre. The network comprises four trusted-node links, each achieving performance metrics suitable for practical deployment. Complementing the experimental work, novel simulations were developed to predict QKD performance using only fundamental parameters such as distance, wavelength, and optical power; marking a clear improvement over models that require broad assumptions or empirical measurements of an existing QKD link. This simulation develops new tools for simulating non-linear effects such as Raman scattering and four-wave mixing, as well as many other aspects of QKD noise, loss, and detection. Validation against UKQNtel measurements showed strong agreement in attenuation modelling and link-level performance. While secret key rate estimates demonstrate the need to account for additional losses, the model provides a robust foundation for network planning and scalability analysis. This research demonstrates a clear pathway toward practical QKD deployment, combining experimental integration with predictive modelling applicable to larger, more complex networks. The results underscore QKD’s potential to become a cornerstone of future secure communications.