Quantum repeaters increase data security

When exchanging sensitive data, for example between banks, communication networks that rely on quantum physics are key to more security. The research cluster “Quantum Repeater Link” (QR.X) is pursuing exactly this goal and just received 35 million EUR funding by the German Ministry of Science and Technology (BMBF). Participants of this research cluster are Prof. Peter Michler, Prof. Jörg Wrachtrup, and Prof. Harald Giessen from the Department of Physics at the University of Stuttgart.

Secure communication is crucial in our highly cross-linked society. Protection against eavesdroppers is ever increasing. Quantum communication offers an elegant solution, yet it is limited to a few hundred kilometers distance due to losses of optical signals at large distances.

Different from classical optical communication, it is not possible to simply use amplifiers to compensate for these optical losses. Rather, so-called quantum repeaters are required for distances above 100 km by linking together smaller parts of the fiber-optical quantum network. The basis for these quantum repeaters are so-called entangled photons, which can for example use the optical polarization of light. Protection against eavesdroppers is secured by the laws of quantum physics.

Research, development, and realization of such quantum repeaters for fiber optical networks are the key goals of the research cluster QR.X. Led by researchers at University of Saarland in Saarbrücken, 43 partners from science and industry collaborate in this cluster. For the first time, researchs will go beyond laboratory experiments with individual quantum repeater elements. Rather, they will put the elements together outside the lab in a real-world fiber-optical network. Advanced concepts such as multiplexing, quantum error correction, and purification of the quantum states will be investigated.

Projects in Stuttgart amount to 6.9 million EUR

The physicists at Stuttgart University were key players when shaping the goals of the research cluster and obtain funding that totals 6.9 Mio EUR. The research is connected to the framework IQST (International Quantum Science and Technology Center) in Stuttgart and Ulm. 

The group of Jörg Wrachtrup at the 3rd Physics Institute is going to investigate a quantum repeater node that consists of two diamond color centers in a field-compatible demonstrator. This project is aiming at scalability of such systems from quantum communication over large distances. The group of Peter Michler at the Institute of Semiconductor Optics is going to investigate and develop ultrabright quantum light sources at emission wavelengths in the telecommunication C-band at wavelengths of 1.55 µm. The entangled photons of these sources transport the fragile quantum information between the different nodes of the quantum repeater.

The research of Harald Giessen is aiming at low-loss, highly efficient coupling of quantum light into single mode telecommunication optical fibers using 3D printed microoptical elements. These tasks represent an indispensable step towards practical quantum communication applications, as every photon counts when taking this advanced technology from the lab into the real world.