Practical continuous variable quantum communication in fibre and free space systems
Christoph Marquardt, Max Planck Institute for the Science of Light
I will review our recent activities in continuous variable QKD that aims for the deployment of QKD equipment compatible with current telecom standards and research in satellite QKD that will make it possible to bridge long distances. In optical fibre systems continuous variable quantum cryptography reaches GHz speed and offers efficient integration with known telecommunication techniques, especially in short inner-city or data center links. Sending and receiving components, including quantum random number generators, can be efficiently built in integrated components. Optical free space communication is a reliable means to transmit classical and quantum information. Free space links offer ad-hoc establishment in intra-city communication, air-to-ground or satellite-to-ground scenarios. In free space quantum communication so far experimental effort had been mostly devoted to discrete variables like the polarization state of single photons. I will present experiments investigating free space transmission of quantum continuous variable states using homodyne measurement, rendering the quantum states immune to stray light and enabling daylight operation. Quantum communication with satellites offers a viable solution to bridge long distances. I will discuss our current activities with TESAT Spacecom and DLR in the development of quantum key distribution with coherent optical communication in satellite systems and show the first quantum-limited measurements from optical states sent from a satellite in GEO-stationary orbit.