Quantum Communications on planetary scale require complementary channels
including ground and satellite links. The former have progressed up to
commercial stage using fiber-cables, while for satellite links, the absence of
terminals in orbit has impaired theirs development. However, the demonstration
of the feasibility of such links is crucial for designing space payloads and to
eventually enable the realization of protocols such as quantum-key-distribution
(QKD) and quantum teleportation along satellite-to-ground or intersatellite
links. We demonstrated the faithful transmission of qubits from space to ground
by exploiting satellite corner cube retroreflectors acting as transmitter in
orbit, obtaining a low error rate suitable for QKD. We also propose a two-way
QKD protocol exploiting modulated retroreflectors that necessitates a minimal
payload on satellite, thus facilitating the expansion of Space Quantum
Communications
