The team of authors implements an experimental Quantum Key Distribution backbone within the framework of the European Quantum Communication Infrastructure initiative. Two network segments are being established: a government-physically protected infrastructure segment for restricted information communications and a public segment in finance and health. The authors share their experience of developing such a network. This experience can be useful to the reader of the article if a similar task is carried out. Also, the provided information can be used to estimate the amount of work, and the finances and time required for it.
The team of authors implements an experimental Quantum Key Distribution backbone within the framework of the European Quantum Communication Infrastructure initiative. Two network segments are being established: a government-physically protected infrastructure segment for restricted information communications and a public segment in finance and health. The authors share their experience of developing such a network. This experience can be useful to the reader of the article if a similar task is carried out. Also, the provided information can be used to estimate the amount of work, and the finances and time required for it.
The purpose of the article was to theoretically determine harmonised criteria for the applicability of quantum key distribution for the protection of critical infrastructure, taking into account the long-term risk of decryption by adversaries possessing quantum computational resources and traffic archiving capabilities. The methodology relied on a theoretical systems analysis of three Quantum Key Distribution subsystems – sources, detectors, and channels (fibre/free space) – complemented by simplified models of the link budget and bit error probability. A concise scenario analysis was conducted for banking networks, energy systems, and government communications, taking into account scalability, compatibility, and cost. The main results showed that laser intensity stability of 1-2% and higher detector efficiencies – 60-70% for Avalanche Photodiodes and 80-90% for Superconducting Nanowire Single-Photon Detectors – extended practical distances and reduced errors. Without trusted nodes in fibre, 150-200 km was achievable; for urban Free-Space Optics lines, 5-20 km was optimal, while longer distances required network segmentation or satellite segments. Architecturally, it was justified that: for banks – rings with trusted nodes and Free-Space Optics reserve; for energy systems – dual fibre channels “control centre-substation” with a local key cache; for government communications – segmented domains with interagency gateways and satellite redundancy. In all scenarios, a Quantum Key Distribution + Post-Quantum Cryptography hybrid with short key rotation and operational countermeasures against attacks on detectors and channels was appropriate, confirming practical suitability for urban and regional networks. The practical significance lay in providing engineering teams in banking, energy, and government communications with ready-made architectural profiles – from rings and dual fibre channels to segmented domains – with Key Management System/Hardware Security Module integration, definition of Service Level Objective/Service Level Agreement, and phased roadmaps. For regulators and operators, this formed a basis for updating requirements and audits, as well as for planning redundancy (Free-Space Optics/satellite) and Total Cost of Ownership categories
The European Union is developing the European Quantum Communication Infrastructure (EuroQCI) as a pan-European network to provide secure communication capabilities across Member States, including governmental and critical-infrastructure domains. While the strategic objective is defined at EU level, the required scale and structure of national quantum key distribution (QKD) networks remain largely unspecified.
This work addresses the question of how to plan and size national terrestrial QKD networks to support critical infrastructure and public authorities. We propose a reproducible planning methodology that estimates network size, total fiber length, and the number of required QKD components based on a small set of explicit assumptions. The approach is demonstrated for Austria, where a synthetic but structured network model is constructed and evaluated using Monte Carlo simulation.
The model focuses on terrestrial QKD infrastructure and explicitly excludes space-based segments. It estimates endpoint counts, trusted repeater node requirements, and hop-length distributions under realistic operational constraints. The Austrian case is then used as a baseline to derive scaling rules for other EU Member States based on population and geographic extent.
The results provide first-order planning estimates for national QKD backbone sizes across Europe. These estimates are not intended as deployment designs but as planning-level references that support early-stage cost assessment and infrastructure dimensioning under the EuroQCI framework.
Quantum communication will play a crucial role on both the terrestrial and space segments. For the deployment of future pan-European quantum communications infrastructures, several projects and missions have already kicked off to launch satellites equipped with quantum key distribution equipment. The Madrid Quantum Communication Infrastructure is based on novel network paradigms like software-defined networking. These features have been integrated into a model-driven simulator developed to be able to incorporate future scenarios involving satellite quantum communications in a flexible and evolutive approach.
Today, we are already using several-component devices and systems based on the technologies developed during the first quantum revolution. Examples include microchips for servers, laptops and smartphones, medical imaging devices, LED, lasers, etc. Now, a second quantum revolution is progressing fast, exploiting technological advances for the ability to engineer and manipulate other quantum phenomena such as superposition, entanglement and measurement. As a matter of fact, there is an impressive increase in research and development activities, innovation, public and private investments in a new wave of quantum services and applications. In this scenario, quantum information and communication technologies (QICTs) can be defined as a set of technological components, devices, systems and methods for elaborating, storing and transmitting/sharing quantum information. This paper addresses the challenges and opportunities enabling the rise of QICTs. In order to provide a concrete example, the paper describes an overview of the European project EQUO (European Quantum ecOsystems) dealing with ongoing innovation activities in the QICT avenue; in fact, EQUO aims at developing and demonstrating the feasibility of QKD (quantum key distribution) networks and their related integration in current telecommunications infrastructures towards the quantum internet.
Progress in the development of techniques for the construction of multiuser quantum communications networks is reviewed in light of the plans for an EU quantum communications infrastructure (EU QCI). Quantum key distribution networks may be classified as trusted node; quantum repeater-entanglement-swapping based; point-to-multipoint based on passive beam splitters, active optical switchers or WDM; high dimensional-multipartite entanglement and flexible reconfigurable multipartite networks. Both satellite and terrestrial implementations are possible and ore both planned for EU QCI; their relative merits are discussed. Current technology falls short in several respects of what is required to address use cases well. Bit rates as a function of distance are currently limited by the characteristics of available devices and are an order of magnitude or more below the theoretical bounds. Non-ideal device behaviour can open loopholes for side-channel attacks. Limited range constrains network geometry. New techniques are being developed to overcome these problems. The more sophisticated schemes depend on ongoing advances in the generation and distribution of entanglement. Particularly promising are the measurement device independent protocol, which eliminates photon-detector related security weaknesses, and the twin-field protocol, which uses similar techniques to extend range, in principle even beyond previously accepted theoretical bounds. Agreement of keys between more than two users can be accomplished classically after pairwise quantum key exchange but direct quantum multipartite agreement using may offer advantages. The same applies to secret sharing. Practical quantum repeaters, to eliminate the need for trusted nodes, are closer to being realised due to recent progress in optical memories.