The joint project quantum link extension (Q.Link.X) that is including 24 research partners from academia and industry is focusing on the extension of quantum communication beyond point to point connections. The long term goal is a physically secure fiber-based network.
As data security and secure communication are becoming increasingly important, quantum communication is a promising approach to achieve highest possible security. Quantum states are used to generate keys and copying an unknown quantum state is forbidden due to fundamental physical laws. Without the possibility to make a copy, a possible eavesdropper cannot learn about the transmitted key without interfering with the signal and thus can easily be detected.
However, due to transmission losses in the optical fiber, the sent information must be reamplified after some tens of kilometers. In classical telecommunication a repeater measures the information and amplifies the signal. In other words, it is making a copy. Since it is forbidden to make a copy of quantum states without interfering with the data, for a quantum network the repeater has to be replaced by a quantum repeater that uses quantum states to store information, without ever measuring them.
Here, at the University of Würzburg, we are researching on a quantum repeater segment based on semiconductor quantum dots in micropillar cavities.