In a networked society, secure communication is essential. Quantum physics delivers the necessary foundation by allowing practicable technologies such as quantum key distribution. With the new fiber optic test facility at the Karlsruhe Institute of Technology (KIT), which opened on January 22, 2025, researchers aim to transmit, test and refine quantum keys. They also plan to set up a quantum network to link quantum computers.
To generate and transmit the quantum keys, the researchers will use cutting-edge technologies such as ultra-coherent lasers with the new fiber optic test facility. Quantum keys are crucial for secure communication because they are based on physical laws instead of the mathematical assumptions underlying earlier encryption keys, which future quantum computers will be able to break.
Spanning 20 kilometers, the quantum-optical transmission line connects laboratories specially equipped with complex lasers and cryostats on KIT’s Campus South and Campus North. The light-guiding core of a fiber optic cable is only about 9 micrometers in diameter. For comparison, the thickness of a human hair is about 60 micrometers.
Important Quantum Research Platform
“Quantum communication is a strategically important field for KIT, so I’m especially pleased that with the finished test facility, KIT is providing its researchers with important infrastructure for investigating the opportunities offered by quantum physics,” said Oliver Kraft, Vice President for Research at KIT. “With this facility, we’re making an important contribution to the advancement of research and development in quantum network technology, with an eye to practical applications.”
“With the fiber-optic test facility, we have a platform for improving quantum key distribution, investigating its basic properties, and integrating it in classical communication,” said Professor David Hunger of the Physikalisches Institut at KIT, who heads the project. Based on this work, the scientists aim to develop new transmission protocols for the keys. “With the new methods we develop, we want to make quantum cryptography more efficient and practical. We’re working on this e.g. with KEEQuant, a quantum communication start-up,” added Hunger. “Furthermore, using novel materials such as molecular quantum emitters, we want to generate ultrapure quantum light – individual photons – to increase transmission rates.”
Building a Quantum Network
The researchers will also be progressively building a quantum network to investigate the quantum internet of the future. Their work focuses on two crucial steps: storing quantum information in special quantum memories, and quantum entanglement of the memories. This will make it possible to implement quantum repeaters for the transmission of quantum information over long distances. Since entanglement is a fundamental aspect of quantum computers, such computers can be connected with one another in a quantum internet via optical transmission of the entanglement.
Test Facility Part of Chem4Quant Cluster of Excellence Initiative
The project is a key part of the infrastructure for the Chem4Quant Cluster of Excellence initiative, in which researchers from KIT, Ulm University and the University of Stuttgart will design materials for future quantum technologies and focus on molecular quantum systems, a new field of quantum technology. In addition, the project plays an important role in the quantum repeater research conducted in the Quantenrepeater.Net (QR.N) joint project of Germany’s Federal Ministry of Education and Research, and in the QuantumBW Innovation Campus.
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Detailed caption: Opening of the fiber optic test facility at KIT: (from left to right) Prof. Sebastian Randel (KIT), Prof. Marc Weber (Head of Division B V, KIT), Prof. Oliver Kraft (Vice President Research, KIT), Prof. Mario Ruben (KIT), Prof. David Hunger (KIT) (Photo: Daryoush Djavadi)
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