Digitalization is penetrating every aspect of our society – from the Industrial Internet all the way to health care applications. This means data safety and secure communications are also becoming more and more important. Quantum communication is a very promising approach in this context: Its information medium is based on quantum states, which, because of fundamental physical laws, can neither be copied nor intercepted without being detected. The German Federal Ministry of Education and Research (BMBF) is supporting this leap into quantum technology by investing a total of 14.8 million Euros in the collaborative project "Quanten-Link-Erweiterung" (Q.Link.X) over the next three years.
"The objectives are optical cable networks that are physically tap-proof," says Q.Link.X project consortium speaker Prof. Dr. Dieter Meschede of the Institute of Applied Physics at the University of Bonn. However, this paradigm shift in information encryption, away from conventional methods and towards quantum technologies, faces a technological challenge: Transmitting quantum information using photons entails unavoidable transmission line losses that up to now have limited the viable transmission distance to less than around 100 kilometers. This limitation is to be overcome without compromising security using quantum repeaters (QR). In classic communications technologies, repeaters prepare and amplify signals. In contrast to these repeaters, quantum repeaters link signals of various sub-segments using quantum processes in order to successfully transmit across greater distances.
The Fraunhofer Heinrich Hertz Institute HHI is one of 24 partners who have joined forces to research the key technologies involved in quantum repeaters. The goal of the Fraunhofer HHI is the provision of an application-oriented test environment consisting of installed optical cables for testing QR components, QR cells and QR segments developed in the consortium. The laboratories of the Fraunhofer HHI will be connected to previously installed optical cables for this purpose. The project will also investigate enhanced protocols in terms of wavelength multiplexing with additional quantum communications and classical transmission channels for existing optical cable communications networks. Transmission segments of between ten and one hundred kilometers in length are to be realized using three different technical platforms: quantum dots, diamond color centers and a combination of atomic and ionic systems. The benefits of the respective systems are to be compared with one another. "Q.Link.X will develop for the first time a quantum repeater that will be tested on installed optical cables. This is an important step towards bringing this technology into the application phase," says Prof. Dr. Ronald Freund, head of the Photonic Networks and Systems department at Fraunhofer HHI.
The Q.Link.X consortium unites a variety of partners ranging from research facilities and universities to industrial laboratories. The close integration of industrial partners and consultants is intended to facilitate from the very beginning the feasibility from an industrial and technical point of view. The exploitation of the results in Germany is to be protected by patents and ensured through spin-off companies originating from the consortium.
The following partners are involved in the project: University of Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn), Technical University of Munich, TU Dortmund University, HighFinesse Laser and Electronic Systems GmbH, Fraunhofer HHI, Technische Universität Berlin, University of Stuttgart, Paderborn University, Saarland University, Freie Universität Berlin, Leibniz Institute for Solid State and Materials Research Dresden, Ruhr-Universität Bochum, Swabian Instruments GmbH, Leibniz University Hannover, Max Planck Institute of Quantum Optics (Garching), Julius-Maximilians-Universität Würzburg, University of Bremen, Heinrich Heine University Düsseldorf, Ulm University, Humboldt-Universität zu Berlin, University of Kassel, Johannes Gutenberg University Mainz, Karlsruhe Institute of Technology and Ludwig Maximilian University of Munich.