Quantum-limited measurements of optical signals from a satellite in geostationary earth orbit

Quantum key distribution (QKD) has raised increased attention over the past years as one of the most attractive quantum technologies for practical implementation. QKD has already been implemented in intra-city networks all around the world. But up to now, bridging global distances with quantum communication remains an outstanding challenge. A promising candidate to provide this link is via optical satellite communication. As space-to-ground communication is already well developed for classical applications, one can make use of the already existing technology for QKD, i.e. modern Laser Communication Terminals (LCTs) may be adapted for quantum communication. An important first step to achieve this goal is a precise characterization of the system and the channel with regard to their quantum noise behaviour.