Unbreakable fibre network connection established between DTU and Niels Bohr Institute

In collaboration with researchers from the Niels Bohr Institute, DTU researchers have demonstrated a 100 per cent secure video connection over the existing fibre network.

Anders Eldrup in conversation with Natasha Friis Saxberg over the quantum-encrypted video link. Photo: Kyv Kyvsgaard, DTU Electro.
Demonstration of quantum-encrypted video link between DTU and the Niels Bohr Institute. Video: Astrid Degerbøl, DTU.

Mathematical encryption challenged

According to Professor Leif Oxenløwe from DTU Electro—one of the researchers behind the new connection—our current mathematically-based encryption will soon be challenged by quantum computers or quantum computer-like systems.

“The risk of hacking is increasing, and many expect that the encryption codes we know today will become insecure within a few years. So there is a real need for us to move away from encryptions based on computational complexity, where you use an algorithm to form a code,” says Leif Oxenløwe.

Quantum computers or similar systems will possess computing power that will make it much, much quicker to break otherwise complicated codes. Breaking a code that today will take an ordinary computer many hundreds of years to break will only take a quantum computer about eight hours, according to one assessment.

Professor Leif Oxenløwe. Photo: Kyv Kyvsgaard, DTU Electro.

Quantum encryption can withstand any attack

There is, therefore, a need for a different form of encryption, and here the use of quantum encryption is an obvious choice. In fact, quantum encryption can demonstrably withstand all attacks on the communication channel because any attempt at eavesdropping will be revealed, and the key can be created using quantum mechanically-based absolute randomness.

“There is a fundamental element of uncertainty associated with quantum mechanics. We can use this to generate encryption keys that are impossible to guess or figure out in any way,” says Leif Oxenløwe.

“We also use single photons—individual light particles—to create the encryption. They are indivisible, meaning the only way to intercept the information they carry is to snatch the photon itself. We will then know right away that someone is on the line, and we can close the line immediately.”

Part of the demonstration also showed what would happen if someone tried to break into the video link. Caterina Vigliar, Postdoc at DTU Electro, played the role of an eavesdropper. The moment she manipulated the link, the connection between Anders Eldrup and Natasha Friis Saxberg was cut. It was only re-established when the attempted eavesdropping was abandoned.

Connection cut. Foto: Kyv Kyvsgaard, DTU Electro.

Quantum encryption: Quantum encryption relies on exchanging so-called quantum keys between sender and receiver protected by quantum technology. Quantum key distribution systems can never be broken, even by the most powerful future quantum computers.

The core of such a system is sharing the key using so-called single photons (light ‘particles’). Any attempt to eavesdrop on the system will require intercepting a photon—which is indivisible—meaning that any attempt at eavesdropping will be detected.

About the project: The quantum encryption link has been developed under the FIRE-Q project—supported by Innovation Fund Denmark—and comprises academic and industrial partners that are now ready to commercialize the technologies. The technology is the result of 20 years of basic research supported by the Danish National Research Foundation through the research centres Silicon Photonics for Optical Communication (SPOC) and Hybrid Quantum Networks (Hy-Q).

The FIRE-Q project also involves Danish companies which, in the long term, can utilize the technologies commercially; Sparrow Quantum—a spin-out from the Niels Bohr Institute—and SiPhotonIC, a spin-out from DTU Electro. In the long term, the demonstration represents an essential step towards a quantum-based Internet where quantum computers can be connected and thus become even more potent.


Denmark is at the forefront when it comes to the use of technology and digital solutions. This brings about great opportunities – but also makes Denmark an obvious target for IT crime. Consequently, there is a great need for research and training in cyber security to ensure that technology continues to create value for people.

Read more in DTU's cyber security topic.