Current status
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We highlight the current state of quantum networks, considering not only recent events and developments, but also previously unmentioned yet important aspects.
Significant advances
The field of quantum communication is evolving rapidly. Numerous breakthroughs are driving the construction of practical and scalable quantum networks. Ultra-low-loss fibres have been developed that minimise photon loss and increase the efficiency of optical transmission. Quantum repeaters are becoming ever more powerful, extending the range of quantum communication and ensuring secure transmission over great distances. Integrated quantum photonics combines several quantum components on a single chip, thereby reducing the size and complexity of quantum devices. Hybrid systems merge classical and quantum technologies to provide versatile and scalable architectures. These innovations shift the boundaries of what is possible and bring us closer to fully exploiting the potential of quantum communication.
Integrated quantum circuits
Integrated quantum photonics—or, more generally, integrated quantum circuits—are micro-chip-like components that manipulate qubits on the microscale. They mark a decisive step toward practical quantum-communication systems, because they allow the miniaturisation and integration of quantum components, much as integrated circuits revolutionised classical electronics. Such circuits are indispensable for scaling quantum computers and quantum-communication systems and enable more compact, efficient devices possible. Advances in photonic integration and solid-state quantum systems lead to more practicable, scalable architectures and thus pave the way for widespread application. Moreover, integrated circuits support the development of complex quantum algorithms and the efficient processing of quantum information—both of which are central factors in the progress of quantum technologies.
Quantum transducers
Quantum transducers—also called quantum converters—enable the coupling of different quantum systems by transferring quantum states from one physical platform to another without destroying the quantum information. One example is converting the state of a microwave photon—typical of superconducting quantum computers—into that of an optical photon, which is suitable for transmission through optical fibres. Quantum transducers are therefore crucial for connecting superconducting qubits with photonic networks. Key types include microwave-to-optical, spin-to-optical, and electro- and optomechanical transducers. Each type is designed for specific system combinations and is intended to guarantee coherence preservation, high conversion efficiency, and low noise.
QKD – Quantum Key Distribution
Quantum key distribution has made the leap from theoretical concept to practical application and is already strengthening secure communication worldwide. Technological progress is overcoming earlier limitations—such as range restrictions and infrastructural challenges—and is making QKD increasingly attractive from an economic standpoint. The following sections present current developments, including quantum repeaters, satellite-based QKD, and fibre-based QKD networks—all of them paving the way for broad adoption.
QKD & quantum repeaters
One of the greatest challenges of QKD is the limited distance over which quantum signals can be transmitted through optical fibres. Over long stretches, loss and noise attenuate the signals and jeopardise security. Quantum repeaters are intended to solve these problems: they extend the reach of QKD networks and regenerate quantum signals without measuring or disturbing them. Acting as intermediate stations, repeaters refresh the signal and forward it, enabling secure communication over hundreds or even thousands of kilometres. Although fully functional quantum repeaters are still under development, initial prototypes point to their enormous potential. Once this technology is mature, it is likely to revolutionise secure long-distance quantum communication.
Satellite-based QKD
To enable global secure communication, QKD must overcome terrestrial boundaries. Satellite-based QKD—precisely what we have encountered as free-space links—offers such a solution without requiring extensive ground infrastructure. In 2016 China placed the satellite “Micius,” the world’s first dedicated to quantum experiments, into orbit. “Micius” successfully demonstrated quantum key distribution between ground stations, including a tap-proof video call between China and Austria separated by thousands of kilometres. This milestone proves the viability of QKD over great distances and lays the foundation for a future global quantum-secure network. International interest has grown accordingly: Europe, Japan, and other regions are pursuing similar projects to realise a worldwide quantum internet.
Fibre-based QKD
Fibre-based QKD uses existing optical networks, particularly fibre cables, to exchange quantum keys securely between sites. The widespread availability of this infrastructure makes QKD a practical option for increasing security in urban and regional networks. Keys are transmitted as photons through the same fibres that carry internet and telecommunication services, facilitating seamless integration into today’s digital infrastructure. Pilot networks already exist—for example in London and Cambridge (UK) and in Zurich and Geneva (Switzerland). These deployments show that QKD can be applied in real communication networks, although signal loss over long distances remains a challenge.
Strategic implications of QKD
The strategic significance of QKD extends far beyond security alone: it is becoming a foundation of national and industrial resilience. Across Europe, governments and companies are investing heavily in quantum communication. A prime example is the EU’s Quantum Flagship initiative, launched in 2018 with a ten-year budget exceeding one billion euros, roughly one quarter of which is allocated to quantum communication. The aim is to build the pan-European quantum-communication infrastructure (EuroQCI), intended to provide highly secure data transmission across the continent.
The EuroQCI initiative links space-based and terrestrial quantum networks in order to bolster Europe’s cyber-security and digital sovereignty. Countries such as the Netherlands are taking a pioneering role with pilot projects that connect government agencies and research institutions. These undertakings are not merely experiments, but proactive steps toward building a resilient communication backbone capable of withstanding future quantum-computing capabilities.
Industry, too, recognises the strategic value of quantum-secure communication. BT (UK) is working with Toshiba to establish QKD links between locations such as London and Cambridge. Swisscom is collaborating with ID Quantique to protect sensitive financial transactions. In France, Orange is testing QKD to provide quantum-secure services for business and public administration.
Challenges for commercialisation
Despite its potential, the commercialisation of QKD faces significant hurdles. High costs for specialised hardware—such as single-photon detectors and quantum repeaters—play a central role, because these components are not yet mass-produced. Moreover, QKD requires a powerful infrastructure for long-distance links; without mature repeaters, range remains limited. Integrating QKD into existing systems poses an additional technical obstacle, as quantum technologies must coexist with classical encryption methods. The absence of standards and regulatory frameworks likewise hampers deployment: companies and public bodies need clear guidelines on implementation and security requirements.
Even so, promising developments are paving the way for broader acceptance. One important trend is the creation of hybrid quantum-secure networks that combine QKD with post-quantum cryptography, offering layered protection against both classical and quantum-based attacks. Advances in hardware—such as integrated photonic circuits and more efficient quantum repeaters—are lowering costs and boosting performance, making QKD more accessible.
With these developments, the vision of a global quantum internet is drawing nearer. In future, satellite-based and fibre-based QKD solutions could work together to create secure quantum links between continents. Such a worldwide network would raise international communication to an unprecedented level of security and fundamentally change how sensitive data are protected across the globe.