From quantum repeaters to the future routers of the quantum Internet
The Internet works so well that we easily forget the extraordinary infrastructure required to carry information across thousands of kilometers. When a signal travels along an optical fiber, it gradually weakens. Classical networks, however, have mechanisms that allow them to receive, regenerate, amplify, retransmit, and route information all the way to its destination. This ability to overcome distance is one of the foundations of the global Internet.
Future quantum networks face the same geographic problem, but the laws of physics that govern them are profoundly different. Quantum states are fragile, photons can be lost as they travel through a fiber, and an unknown quantum state cannot simply be copied to produce a new, perfect version of the signal. The methods used for decades in classical telecommunications therefore cannot be transposed directly to the quantum world.
Building quantum networks capable of covering long distances one day will require a new architecture. Quantum memories and future quantum repeaters could become essential components of it. Their role helps explain one of the most significant challenges that still separates today's experiments from a true quantum Internet: how do you distribute a fragile quantum resource over long distances without having to establish a perfect direct link between every system?
In a classical network, information can be represented as bits. Even when the physical signal carrying them degrades, the information can be reconstructed. An intermediate device can receive a signal that is still legible enough, determine the data it contains, and generate a new signal that will continue on its way. The original information therefore does not need to travel physically intact across the entire distance separating its point of origin from its destination.
The quantum world imposes a fundamentally different constraint: the no-cloning theorem forbids creating arbitrary perfect copies of an unknown quantum state. This property profoundly changes a network's architecture. When a quantum signal weakens, it is not possible to simply read it, copy it, and retransmit it the way you would with classical information. The measurement itself can alter the very state you are trying to preserve.
Optical fiber adds a further difficulty. It is an excellent transmission medium, but it is not perfectly transparent. The farther a photon travels, the lower the probability that it will reach its destination. For classical communication, various mechanisms make it possible to progressively compensate for this attenuation. In quantum communication, losing the photon can also mean losing the quantum resource it was carrying.
One solution is to rethink distance itself. Rather than trying to establish a quantum connection directly between two extremely distant points, the path can be divided into several shorter segments. Entanglement can be established on each of these segments, while intermediate devices temporarily hold the necessary states. Quantum operations then make it possible to progressively extend the entanglement so that it links systems that are farther apart.
That is the general principle behind quantum repeaters. Their name, however, can create a misleading analogy with repeaters in classical telecommunications. They do not simply receive a weak signal in order to produce a stronger copy of it. They operate on quantum mechanisms that make it possible to progressively build a connection across several segments without having to arbitrarily copy the quantum state being transmitted.
Quantum memories then become indispensable. In a network made up of several segments, not all of the required operations will necessarily succeed at the same instant. One segment may be ready while another is not yet. It must therefore be possible to temporarily hold certain quantum states while the rest of the network gets ready. Memory makes this synchronization possible.
What seems trivial in a classical computer represents a considerable challenge in the quantum world. Quantum states are particularly sensitive to interactions with their environment and can quickly lose the properties you want to exploit. Preserving them long enough, with sufficient quality, and in a way that still allows them to be used in network operations is therefore a major scientific and engineering problem.
This architecture also leads to thinking differently about what a network carries. The Internet is primarily designed to move information between destinations. In a quantum network, entanglement itself can become a resource to be created, stored, distributed, and used. The network might therefore need to know not only the origin and destination of a request, but also the availability and quality of the quantum resources required to fulfill it.
This difference helps explain why people are sometimes beginning to talk about future "quantum routers," even if the analogy with Internet routers must be used with caution. A classical router and a quantum repeater do not perform the same function. The common idea lies instead in the need for intermediate infrastructure. A global Internet would be impossible if every device had to be physically connected directly to every other one. In the same way, a large-scale quantum network will probably not be able to depend on direct links between every pair of quantum systems.
Intermediate nodes capable of taking part in the creation and distribution of quantum resources will therefore be needed. Mechanisms will have to provide temporary storage, synchronization, and the extension of entanglement. As networks grow more complex, other functions may become necessary to determine how the available resources should be used and along which paths they can be established. Moving from a few experimental links to a genuine network will therefore require far more than the ability to send a photon over a long distance.
That is precisely what makes recent experiments using quantum memories over links representing several hundred kilometers of fiber so interesting. Their importance does not lie solely in the distance announced. A laboratory experiment is obviously not a commercial network connecting cities and delivering continuous services to thousands of users. The scientific value lies above all in demonstrating architectures that could overcome certain limits of direct quantum transmission.
This distinction is essential. The question is not simply how far a photon can travel. The real challenge is understanding how to build a network capable of operating when distance becomes too great to rely on a direct link alone. Quantum memories and repeaters thus represent possible elements of an architecture meant to turn a physical constraint into a network problem that can gradually be mastered.
The step from the laboratory to usable infrastructure nevertheless remains considerable. Memories will have to preserve quantum states with sufficient quality and for a sufficient length of time. Equipment will have to become more reliable and reproducible, error rates will have to be controlled, and the technologies will have to work in conditions far less controlled than those of a laboratory. Interoperability between equipment from different manufacturers will also become essential, as will the standardization of protocols, the reduction of costs, and the ability to administer these infrastructures at scale.
To this is added an important reality: quantum networks will themselves need classical infrastructure. Equipment will have to coordinate, certain information will have to be exchanged, operations will have to be synchronized, and systems will have to be administered. Identities will have to be authenticated, configurations applied, and incidents detected. Quantum infrastructure may provide a new physical capability without eliminating the IT mechanisms required to operate it.
This interdependence will have direct consequences for cybersecurity. A quantum technology can exploit remarkable physical properties while the classical system that administers it remains exposed to software vulnerabilities, a compromised identity, or a misconfiguration. Security will therefore have to cover the entire chain, from the quantum resource through to the interfaces, control systems, and governance mechanisms that make it usable.
This reality connects directly to Hypersecurity. In a hybrid infrastructure, the robustness of any one component is not enough to determine the security of the whole. You have to understand the interactions between layers, the identities that can trigger operations, the levels of trust granted, the dependencies on suppliers, and the consequences of a failure. Future quantum networks will add new resources to govern, but many of the fundamental questions will remain familiar.
If entanglement becomes a network resource, it will be necessary to determine who can request it, for which application, with what priority, and at what level of quality. It will be necessary to know which nodes can take part in an operation, which organizations control that infrastructure, how to measure a service's performance, how to ensure its traceability, and how to react when a resource becomes unavailable. The physics changes; the needs for architecture, governance, and continuity remain.
New dependencies will also appear. Companies will most likely not all build their own quantum infrastructure. Certain capabilities may be consumed from telecommunications operators, specialized providers, research centers, technology platforms, or other partners. It will then be necessary to know the critical suppliers, the standards used, the location of the infrastructure, the alternatives available, and the applicable jurisdictions. Digital sovereignty will gradually extend to these new technology layers.
For the vast majority of organizations, this outlook obviously does not justify buying a quantum repeater right away. Understanding its role nevertheless has strategic value: it helps distinguish structural scientific advances from spectacular announcements and to follow the evolution of the building blocks that could make future commercial networks possible. Telecommunications, scientific research, defense, financial services, critical infrastructure, and environments handling particularly sensitive information may encounter these technologies earlier than others.
Preparation must therefore remain proportional to real needs. Some organizations will need to follow progress in quantum networks closely, while others can simply fold this development into their technology watch. In both cases, understanding the fundamental principles makes it possible to make better decisions when the technology starts to leave the laboratory.
Classical networks were able to become global because we learned to carry, regenerate, and route information efficiently over very long distances. Quantum networks must solve a comparable problem while respecting profoundly different laws of physics. The fragility of quantum states, losses in fiber, and the impossibility of arbitrarily copying an unknown state prevent us from simply reproducing the methods that allowed the Internet to conquer the planet.
Quantum memories and repeaters represent one possible answer to this challenge. By dividing long distances into segments and making it possible to hold and then progressively extend entanglement, they could become some of the fundamental building blocks needed to move from experimental links to genuine distributed quantum networks. The progress being made today still amounts only to steps toward that ambition, but it does help us better understand the architecture that could eventually make it possible.
For organizations, the current challenge is above all to develop enough understanding to distinguish an important scientific discovery from a technology ready to be deployed. As quantum networks advance, questions of integration with classical infrastructure, identity, cybersecurity, governance, supplier dependency, resilience, and sovereignty will gradually become as important as quantum performance itself.
At Quantum Beyond, our role is precisely to follow these developments with that dual perspective. Specialists in quantum physics, memories, repeaters, and telecommunications will continue to advance the fundamental technologies. Our experts can work alongside internal teams and these specialized partners to help organizations understand how these new capabilities might one day fit into their architectures, their security mechanisms, and their operations.
A global quantum Internet will not be born from a single discovery. It will result from many scientific and industrial advances that will progressively have to become reliable, interoperable, manageable, and economically viable.
Overcoming distance is one of those fundamental challenges. Quantum memories and repeaters could be among the technologies that will one day make it possible to turn that distance into a genuine network.