Satellite-to-ground quantum-limited communication using a 50-kg-class microsatellite

The recent rapid growth of satellite-constellation programmes for remote sensing and communications, enabled by the availability of small-sized and low-cost satellites, has provided impetus for the development of high-capacity laser communication (lasercom) in space. Quantum-limited communication can enhance the performance of lasercom and is also a prerequisite for the intrinsically hack-proof secure communication known as quantum key distribution. Here, we report a quantum-limited communication experiment between a microsatellite (48 kg, 50 cm cube) in low Earth orbit and a ground station. Non-orthogonal polarization states were transmitted from the satellite at a 10 MHz repetition rate. On the ground, by post-processing the received quantum states with ∼0.146 photons per pulse, clock data recovery and polarization reference-frame synchronization were successfully achieved, even under remarkable Doppler shifts. The quantum states were discriminated by a receiver with four photon counters, with a quantum bit error rate below 5%, validating the applicability of our technology to satellite-to-ground lasercom and quantum key distribution.