Tap-proof communication is of central importance for a networked society. Quantum physics provides the basis for this: it enables practical technologies such as quantum key distribution. With a new fiber-optic test track at the Karlsruhe Institute of Technology (KIT), which was opened on January 22, 2025, researchers want to transfer, test and further develop such keys. In addition, they want to build a quantum network that, among other things, enables the linking of quantum computers.

Quantum keys are crucial for secure communication

With the new fiber-optic test track, the researchers use state-of-the-art technologies such as highly coherent lasers to generate and transmit the quantum keys. These are crucial for secure communication, as they are based on physical laws and not, as in the case of previous keys, on mathematical assumptions that can be broken with future quantum computers. With a length of 20 kilometers, it connects specially equipped laboratories with elaborate lasers and cryostats at the KIT's South and North campuses as a quantum optical transmission link. The light-conducting core of the fiber optic cable has a diameter of only about 9 micrometers. By comparison, a human hair is about 60 micrometers thick.

Important platform for quantum research

“The topic of quantum communication is of great strategic importance for KIT. I am all the more pleased that the test track built by KIT provides researchers with an important infrastructure for exploring the possibilities of quantum physics,” says Professor Oliver Kraft, Vice President Research at KIT. ”We are making a decisive contribution to advancing research and development in the field of quantum network technologies and bringing them to applications.”

Novel transmission protocols for the keys

“With the fiber-optic test track, we now have a platform for further developing quantum key distribution, conducting fundamental characterizations, and integrating it into classical communication,” says project manager Professor David Hunger from the KIT Institute of Physics. Building on this, the scientists are developing novel transmission protocols for the keys. “We want to use new methods to make quantum cryptography more efficient and practical. For example, we are working with KEEQuant, a start-up company in the field of quantum-safe communication,” Hunger explains. ”With the help of special materials, we want to generate highly pure quantum light – that is, individual light particles – and thus increase transmission rates.”

Structure of a quantum network

In addition, the researchers are building a quantum network in several stages to explore the future quantum internet. They are focusing on two essential steps: firstly, the storage of quantum information in special quantum memories and, secondly, the quantum mechanical entanglement of the memories. This makes it possible to implement quantum repeaters that can transmit quantum information over long distances. Since entanglement is a basic element of quantum computers, they can be connected to each other by optically transmitting the entanglement in a quantum internet.

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