Quantum Key Distribution (QKD) is a ground-breaking method of secure communication that harnesses the principles of quantum mechanics. It enables two parties to generate a shared random secret key, known only to them, which can be used to encrypt and decrypt messages. The primary goal of a quantum key distribution network is to provide secret keys to any users or applications that require a high level of security.

Broadening the Horizons of Point-to-Point Quantum Key Distribution Systems

Traditionally, QKD has been implemented between two nodes, often referred to as Alice and Bob. However, the evolution of quantum networks has seen the expansion of QKD beyond these two nodes. This expansion is facilitated by the integration of quantum repeaters and trusted nodes, which act as intermediaries between current QKD systems that only have trusted nodes and the future Quantum network will be built on configurable and routable QKD nodes. In this scenario, QKD can be deployed efficiently and practically, while also offering valuable insights for the future true Quantum Network.

The QKD networks also promise to offer better cost-effectiveness compared to the current point-to-point systems.

The transition from a fixed two-node QKD system to a self-evolving QKD network will be realized through the use of a software-defined network managed by centralized Network managers. These Software Defined Networks (SDN) consist of QKD nodes, which are interconnected through either direct optical links or virtual links (via multiple hops), forming a network that provides secure key distribution service across geographical boundaries, surpassing the fixed distance offered by direct fibre.

To enhance the key generation efficiency in such networks, dynamic routing strategies have been developed, which are based on the current state of the network. The routing functions use advanced path-finding algorithms which adapt to changes in the network status of the nodes and links.

The Significance of Quantum Networks

The QKD networks will offer a higher level of services through key management system (KMS) links enabling seamless distribution of secure keys across the vast network.

The Benefits of Quantum Software-Defined Networking (SDN)

SDN is an innovative approach to networking that uses software controllers to manage network traffic. By leveraging software, SDN can create and operate a series of virtual overlay networks that work in conjunction with a physical underlay network. SDN offers several advantages over traditional networking architectures, including:

• Centralized Network Control: SDN centralizes the control of the network in a single controller, simplifying the management and configuration of the network.
• Operational Efficiency: SDN provides seamless network control, operational efficiency, and accelerated business results.
• Flexibility and Scalability: SDN offers greater flexibility and scalability in the network, as the data plane can be reprogrammed in real time to adapt to changing network conditions.

The QKD SDN is standardized by ETSI which has a series of standards defined such as ETSI GS QKD 015 and ETSI GS QKD 018 and more under the standardization process. This topic is important from a compliance perspective as it involves the interoperability of networks and the ecosystem of network vendors, which requires standardization.

The QKD SDN network will run parallel to the optical SDN, which will switch the light paths to achieve the optical fibre network required for the key quantum links. Such SDNs of QKD and the OTN (optical Networks) will be orchestrated by the centralized Network Manager (SDN Orchestrator). Thus, the network manager will be the centralized orchestrator of the whole network of networks, providing the operational control, performance monitoring, configuration, and charging policy management functions for the complete QKDN.

These QKD networks will be self-organizing in way of handling the discovery of new QKD nodes to the network linking them to the other nodes and continuously evolving the mesh of path for the connectivity. The path functions are intelligent to find the best path for connecting the nodes for secret key delivery considering the QOS specified by the application. The centralized QKDN Controller controls the QKD network continuously to handle all the faults, changes in QOS needs and selection of best paths for uninterrupted secret key delivery.

The following figure illustrates the overall network of QKDN (QKD Networks), centrally managed (orchestrated) by an NM.

Future Prospects of Quantum Networking

The prospects of quantum networking are vast and thrilling. As quantum networks continue to evolve and advance, they have the potential to revolutionize various fields, including:

• Quantum Computing: Quantum networks are a crucial component of quantum computing systems, enabling distributed quantum computing and the sharing of computational resources.
• Quantum Communication: Quantum networks facilitate secure communication through QKD and quantum teleportation, ensuring the confidentiality and integrity of transmitted information.
• Quantum Sensing: Quantum networks can be used for high-precision sensing applications, such as detecting gravitational waves and analysing complex physical systems.
• Quantum Cryptography: Quantum networks provide a foundation for developing advanced cryptographic systems, offering unparalleled security in the digital world.
• Quantum Internet: A world of secure connected world of nodes across the globe enabling end-to-end security.

Conclusion

The integration of QKD, quantum networks, and SDN represents a significant advancement in the field of secure communications. As we move beyond two-node QKD, we open up new possibilities for secure, efficient, and scalable networks.

These networks which can be centrally controlled, scaling, fault-tolerant, self-evolving and providing uninterrupted quality of service to the various applications are set to be state of the art for the next quantum communication era. Currently, some of the leaders in the QKD domain have started deployment of the ETSI-compliant QKD networks.  QNu Labs, which is among the leading companies globally in the QKD domain is deploying QKD networks.

The future of secure communications lies in the successful integration of these technologies, paving the way for a new era of quantum networks.