Towards quantum communication with Europe´s western coast

Physicist Hannah Thiel will prepare for a quantum communication link between the optical ground stations in Innsbruck (Austria) and Vigo (Spain). In our everyday lives we send, receive, and save a large amount of sensitive data that needs to be kept secret to avoid malicious use. Luckily there is a method for encoding data that, if implemented well, cannot be broken. Quantum cryptography relies on fascinating quantum phenomena like the no-cloning theorem and entanglement. As carriers for the quantum information we employ single photons. Among the different quantum cryptography methods quantum key distribution is the most advanced with optical-fiber-based options already commercially available. With those we can provide quantum- safe keys to metropolitan areas. However, optical fibers are lossy and distort the information carried by the photons. To cover larger distances, we prefer to send photons to and from satellites. The photons only traverse 20km of atmosphere with relatively low loss and then travel through vacuum practically unperturbed. This allows us to establish a secret key first between the satellite and one ground station and then later with another ground station. This way we effectively realize quantum secure communication between two ground stations thousands of kilometers apart. So far only the Chinese satellite Micius has shown quantum key distribution, but many quantum satellite missions are planned. However, since the development of this technology is only now gaining momentum, many design parameters are still in flux. This complicates the design of the ground stations which need to be prepared for quantum information encrypted in different ways and sent at different wavelengths at extremely low signal levels. In this project we will identify how to best evaluate the performance of the quantum optical ground stations and determine benchmarking criteria. This is done by characterizing two ground stations that are being installed in Vigo, Spain and Innsbruck, Austria. Additionally, we will set up testbeds recreating realistic conditions encountered in an optical link with a low-earth orbit satellite. This allows us to test quantum communication equipment and methods without the need for an actual link to a satellite. Finally, we will study and ensure the compatibility of the two quantum optical ground stations to enable a quantum-secure communication link across Europe.