We provide various results about the transmission capacity of quantum networks. Our primary focus is on algorithmic methods to efficiently compute upper-bounds to the traffic that the network can handle at most, and to compute lower-bounds on the likelihood that a customer has to wait for service due to network congestion. This establishes analogous assertions as derived from Erlang B or Erlang C models for standard telecommunications. Our proposed methods, while specifically designed for quantum networks, do neither hinge on a particular quantum key distribution technology nor on any particular routing scheme. We demonstrate the feasibility of our approach using a worked example. Moreover, we explicitly consider two different architectures for quantum key management, one of which employs individual key-buffers for each relay connection, the other using a shared key-buffer for every transmission. We devise specific methods for analyzing the network performance depending on the chosen key-buffer architecture, and our experiments led to quite different results for the two variants.
We provide various results about the transmission capacity of quantum networks. Our primary focus is on algorithmic methods to efficiently compute upper-bounds to the traffic that the network can handle at most, and to compute lower-bounds on the likelihood that a customer has to wait for service due to network congestion. This establishes analogous assertions as derived from Erlang B or Erlang C models for standard telecommunications. Our proposed methods, while specifically designed for quantum networks, do neither hinge on a particular quantum key distribution technology nor on any particular routing scheme. We demonstrate the feasibility of our approach using a worked example. Moreover, we explicitly consider two different architectures for quantum key management, one of which employs individual key-buffers for each relay connection, the other using a shared key-buffer for every transmission. We devise specific methods for analyzing the network performance depending on the chosen key-buffer architecture, and our experiments led to quite different results for the two variants.
Quantum Key Distribution allows the exchange of symmetric keys with information-theoretic security between adjacent nodes. Key relay techniques in Quantum Key Distribution Networks (QKDNs) address the need for symmetric keys between nodes that are either too distant for establishing a quantum link or separated by intermediate nodes. The Secure Key Rate is limited, which triggers a need to use buffers (Quantum Key Pools) to store keys for later use. The secure key relay uses One-Time Pad, thus the number of links in the route impacts the number of keys used to deliver a pair of symmetric keys. The need for efficient routing algorithms in QKDNs has led to different routing algorithms. This work revisits some routing approaches that have been improved here. Results show that using asymmetrical link costs reduces blocking, a Long Short-Term Memory approach is enhanced by including cross-validation, and finally some strategies to reduce management traffic are proposed.
A first quantum revolution has already brought quantum technologies into our everyday life for decades: in fact, electronics and optics are based on the quantum mechanical principles. Today, a second quantum revolution is underway, leveraging the quantum principles of superposition, entanglement and measurement, which were not fully exploited yet. International innovation activities and standardization bodies have identified four main application areas for quantum technologies and services: quantum secure communications, quantum computing, quantum simulation, and quantum sensing and metrology. This paper focuses on quantum secure communications by addressing the evolution of Quantum Key Distribution (QKD) networks (under early exploitation today) towards the Quantum-ready networks and the Quantum Internet based also on entanglement distribution. Assuming that management and control of quantum nodes is a key challenge under definition, today, a main obstacle in exploiting long-range QKD and Quantum-ready networks concerns the inherent losses due to the optical transmission channels. Currently, it is assumed that a most promising way for overcoming this limitation, while avoiding the presence of costly trusted nodes, it is to distribute entangled states by means of Quantum Repeaters. In this respect, the paper provides an overview of current methods and systems for end-to-end entanglement generation, with some simulations and a discussion of capacity upper bounds and their impact of secret key rate in QKD systems.
In the coming years, quantum networks will allow quantum applications to thrive thanks to the new opportunities offered by end-to-end entanglement of qubits on remote hosts via quantum repeaters. On a geographical scale, this will lead to the dawn of the quantum internet. While a fullblown deployment is yet to come, the research community is already working on a variety of individual enabling technologies and solutions. In this article, with the guidance of extensive simulations, we take a broader view and investigate the problems of quality of service (QoS) and provisioning in the context of quantum networks, which are very different from their counterparts in classical data networks due to some of their fundamental properties. Our work leads the way toward a new class of studies that will allow the research community to better understand the challenges of quantum networks and their potential commercial exploitation.
In quantum key distribution (QKD) networks, the quantum service channel (QSCh) is highly sensitive to link failures, as any interruption in the quantum channel can immediately halt key generation, and hence the transmission of secured data across optical networks. Hence, robust protection mechanisms are essential to ensure continuous secure key distribution. However, conventional protection approaches, such as dedicated protection and fixed-path routing, often suffer from low resource efficiency and poor adaptability to heterogeneous relay environments. To ensure both survivability and efficient resource allocation in QKD based optical networks, we propose a shared path protection scheme based on hybrid relays. In the proposed approach, K-candidate paths are computed for both the traditional data channel (TDCh) and QSCh, and the working path is selected using a weighted metric that considers both the hop-count and the security degree. To enhance resilience, the shared protection paths are established, allowing multiple backup paths to reuse network resources for connection requests. A connection request is accepted only if both the working and the protection paths are successfully reserved, thereby ensuring strong protection. The system incorporates joint allocation of wavelength and time-slot, and introduces a protection threshold to support shared use of backup resources. Simulation results show that the proposed method achieves lower blocking probability, while maintaining high wavelength and time-slot efficiency compared to the baseline methods in different networks.
Optical communications provide high capacity and scalability, while quantum communications, particularly through quantum key distribution (QKD), enable information-theoretic security. However, it still remains challenging to deliver both high throughput communication and long-term security within a hybrid quantum-classical optical network. Specifically, classical optical resources can be reallocated to support QKD, aiming to achieve synergistic resource utilization that surpasses the sum of individual functionalities. In this work, we formulate a networking model that captures the resource allocation constraints, aiming to figure out the necessary conversion of classical optical resources to QKD capacity while maintain the connectivity of classical optical communication. Based on that, we propose a synergistic resource allocation strategy, implemented through heuristic routing, wavelength assignment, and power configuration (SRWP) algorithms. Simulation results demonstrate that the proposed SRWP algorithm, with the objective of network-wide average secret key rate (SKR) maximization (SRWP-ARM), enhances the average SKR from the order of kbit/s to Mbit/s at GHz-level pulse repetition rates. In a 9-node mesh network topology with 50 km links, the algorithm achieves this gain with zero service blocking under a traffic load of 100 erlangs. At a higher load of 300 erlangs, it maintains a service blocking probability as low as 1.24% while still achieving an average SKR of 18.05 kbit/s. This represents the best trade-off between classical service connectivity and secret key generation across all evaluated algorithms.
The main purpose of a quantum key distribution network is to provide secret keys to any users or applications requiring a high level of security, ideally such as to offer the best protection against any computational attack, even of a quantum nature. The keys shared through a point-to-point link between a source and a detector using a quantum key distribution protocol can be proven information-theoretically secure based on the quantum information theory. However, evaluating the security of a quantum key distribution network, especially if it is based on relay nodes, goes far beyond the quantum security of its single quantum links, involving aspects of conventional security for devices and their communication channels. In this contribution, we perform a rigorous threat analysis based on the most recent recommendations and practical network deployment security issues. We show that, at least in the current state of our understanding of quantum cryptography, quantum key distribution networks can only offer computational security and that their supposed resilience to quantum cryptanalysis requires resorting to post-quantum cryptography.