Cybersecurity through quantum networks TU Braunschweig researches efficient data transmission

Almost every day we hear reports of IT sabotage, espionage or ‘hybrid warfare’. Networks based on quantum physics could provide a high level of security. Quantum repeaters are the basis for this. TU Braunschweig is developing communication protocols for such networks to increase their efficiency and performance. TU Braunschweig is part of a research project funded by the German Federal Ministry of Education and Research (BMBF) since January 2025, which aims to demonstrate quantum repeater concepts on test tracks outside the laboratory environment.

Structure of a miniaturised ion trap for use in a quantum repeater node on a fibre testbed. Photo credits: © Saarland University / Künzer Kommunikation

We all know them from our own homes, where they eke out an existence in remote power sockets, sending home Wi-Fi to corners of the house that would otherwise be inaccessible with the router alone: repeaters. Cleverly placed, these small devices significantly extend the range of data transmission. Many scientists in Germany are also researching repeaters. However, they are not talking about the kind of repeaters you can buy in a shop, but about quantum repeaters, which are much more complex. In the newly established research project ‘Quantumrepeater.net (QR.N)’, a total of 42 partners from research and industry will make further progress in researching and establishing quantum networks.

For free societies and the protection of critical infrastructures

The figure shows the achievable quantum key distribution rates (white: without repeater, light green: with one repeater and dark green: with multiple repeaters). Image credits: Loock, P et al: Extending Quantum Links: Modules for Fibre- and Memory-based Quantum Repeaters. Advanced Quantum Technologies, 2020, 1900141.

In the future, such networks could be crucial for free societies and the protection of critical infrastructure – just think of the rapidly growing number of acts of IT sabotage that are increasingly undermining the networked world. Quantum networks would offer a whole new level of security. The quantum physical principles on which such a network is based make it extremely secure against espionage or sabotage. Quantum repeaters, which enable the secure transmission of information over long distances and thus make quantum networks possible, therefore make an important contribution to the creation of a quantum-secure IT infrastructure. They also offer the prospect of secure networking for future quantum computers.

Technical challenge

“The realisation of quantum repeaters and, in the future, end-to-end quantum networks is an enormous technical challenge,” explains Christoph Becher, Professor of Quantum Optics at Saarland University and spokesperson for the QR.N research network. The quantum states for communication in a quantum network must be generated, stored and transmitted with high quality and as little loss as possible. But to turn a simple connection between two points into an entire network, you need nodes that temporarily store these quantum states and ensure that they are transmitted to the next node – repeaters, in other words.

“On the one hand, we want to set up intermediate nodes between two end points of a network connection, install quantum memories at these nodes and perform gate operations,” says Professor Becher. “This should provide a quantum advantage in transmission and enable error correction for more powerful quantum repeater protocols.”

More efficiency, more data, more security

As part of the joint project, Dr Christian Deppe’s research group at Technische Universität Braunschweig’s Institute of Telecommunications is working on ‘Entanglement-assisted communication in networks with quantum repeaters’. Communication protocols for quantum repeater networks are being developed to increase efficiency and performance. One focus is on the further development of post-Shannon protocols that exploit new effects of quantum mechanics to significantly reduce the amount of data and increase the simultaneous transport of information. In computing, for example, quantum entanglement plays a key role in reducing the number of computational steps required by qubits. In communications, quantum entanglement can be used as a resource to improve the performance of classical communications. It also ensures the secure exchange of keys between communication partners, since any attempt to eavesdrop changes the state of the quantum information and is thus detected.

The figure shows a scheme of point-to-point quantum communication with a repeater by creating entanglement between the sender and receiver. Image credits: Loock, P et al: Extending Quantum Links: Modules for fibre- and memory-based quantum repeaters. Advanced Quantum Technologies, 2020, 1900141.

In particular, TU Braunschweig is researching variants of superdense coding, which allows two classical bits to be transmitted via one qubit. “A proof of concept in a laboratory environment will validate the practical suitability of the technologies. The aim is to improve the fundamentals and applications of entanglement-based communication and to make networks more secure and powerful through quantum resources,” says Dr Christian Deppe from the Institute of Telecommunications in Braunschweig.

No established hardware base yet

Another research question that the QR.N partners are addressing concerns the hardware on which the quantum network is based. This is because there is currently no established hardware basis in research. Individual atoms and ions, semiconductor structures, artificial atoms in diamonds and rare-earth atoms could form the basis for quantum storage and quantum networks. “Therefore, we also want to look for cross-platform methods and protocols and combine different hardware platforms into hybrid systems in order to ultimately achieve hardware-independent quantum nodes,” says Professor Becher. In addition, the participating institutions want to support existing ‘classical’ communication networks with methods of quantum entanglement, the basic principle of quantum technology.

One of the declared goals of the project consortium is to develop the basis for establishing quantum-secure communication in Germany within a few years. This is of great importance to society, especially with regard to IT security and the protection of critical infrastructures. “In the longer term, quantum repeaters will contribute to the development of quantum information technology for public communication systems.”

So quantum repeaters won’t be mass-produced by electronics shops like their inconspicuous brothers and sisters in power sockets up and down the country. But their importance to our society will be all the greater.

Project data

The ‘Quantenrepeater.Net (QR.N)’ project started on 1 January 2025. It is funded by the German Federal Ministry of Education and Research (BMBF) with a total of €20 million over three years. A total of 42 research institutions and companies are working together to develop the basic building blocks of a quantum network structure based on quantum repeaters.

The project builds on the results of the BMBF-funded ‘Quantum Repeater.Link (QR.X)’ project, which, under the leadership of Christoph Becher, investigated the fundamentals for the development of a quantum repeater throughout Germany from 2021 to the end of 2024. This was preceded by other projects since 2010.