Advances in Receiver and Detection Systems for Low Earth Orbit Nanosatellite Quantum Communications

Satellite quantum communications have received a surge of interest in recent years, encouraged by the success of the QUESS experiments and as a reaction to advances in quantum computing. This work focuses on low Earth orbit nanosatellite missions, which offer several benefits (e.g. lower costs, greater launch availability, easier to replenish) over satellites at different orbit heights (medium Earth orbit, geosynchronous Earth orbit) and satellite size classes (e.g. small-sats, etc). Recent work on low Earth orbit satellite Quantum Key Distribution (QKD) has focused on transmitters and quantum sources, with less attention paid to the receiver side of the link. This review addresses that imbalance by focusing on the receiver and detection systems of satellite quantum communications. This work has found that two-way beacon acquisition and tracking systems are both a common element of state-of-the-art missions, and likely to remain a critical subsystem to ensure high-quality satellite-to-ground station links; however, improvements to detection and tracking algorithms could be made. For discrete variable QKD, receivers and detection systems in nanosatellites at low Earth orbit are likely to remain using silicon single photon avalanche diodes, while receivers and detection systems in optical ground stations may opt for superconducting nanowire single photon detectors, as cryogenic cooling is feasible. For continuous variable QKD, the receivers and detection systems, using coherent detection systems, share many hardware elements with classical optical satellite communications. Combined with coherent detection systems’ inherent resilience to operating during daytime conditions, this makes continuous variable QKD an attractive prospect for future missions, if its fundamental challenges can be overcome.