A quantum network is based on the transmission of individual photons, which serve as "mobile" quantum bits. The probability that such a light particle arrives at the receiver generally decreases as the optical fiber distance increases. In order to exchange data over distances of 10 to 100 km or more, the photons must therefore have a certain wavelength. But even then, intermediate stations are necessary for a continental network in which the signal is processed. However, these quantum repeaters differ fundamentally from signal amplifiers used in classical communication technology.
Quantum repeaters have to bridge the sections using quantum effects. They are based on the interference of individual light particles emitted by spatially separated, independent emitters. "In our case, we use semiconductor nanostructures as emitters of the light particles. They emit photons at a very high frequency," explains Jonas Weber, who was responsible for photon generation and interference in the project. "This is important for fast data transmission," says the PhD student at the Institute of Semiconductor Optics and Functional Interfaces (IHFG) at the University of Stuttgart.