High performance optical free-space links for quantum communications

Secure communication networks are the critical infrastructure of the information age. To ensure secure communication between governmental institutions and other high-security environments, the German Federal Ministry of Education and Research (BMBF) initiated an ambitious project - the QuNET initiative. In a joint effort, the Max Planck Institute for the Science of Light (MPL), the German Aerospace Center (DLR) and the Fraunhofer Society aim to develop the technological basis of a German quantum key distribution (QKD) infrastructure. This paper describes the infrastructure used in a first link demonstrator within this project and how we achieved the transition from initial quantum transceiver concepts to first link experiments.