The first exchange of a few photons per pulse has been performed between two different satellites 20,000 kilometers apart. This was between the Russian GLONASS constellation and the Space Geodesy Centre of the Italian Space Agency.

The longest channel length previously demonstrated was around 7,000 km, in an experiment using a Medium-Earth-Orbit (MEO) satellite that we reported in 2016.

Arxiv – Towards quantum communication from global navigation satellite system (8 pages).

Quantum Science and Technology – Towards quantum communication from global navigation satellite system

Satellite-based quantum communication (QC) is an invaluable resource for the realization of a quantum network at the global scale. In this regard, the use of satellites well beyond the low Earth orbit gives the advantage of long communication time with a ground station. However, high-orbit satellites pose a great technological challenge due to the high diffraction losses of the optical channel, and the experimental investigation of such quantum channels is still lacking. Here, we report on the first experimental exchange of single photons from a global navigation satellite system (GNSS) at a slant distance of 20 000 km, by exploiting the retroreflector array mounted on GLONASS satellites.