Single-Photon Detectors for Satellite and CubeSat Quantum Key Distribution: A Systematic Evidence Map

Advancing satellite and CubeSat quantum key distribution (QKD) requires receiver-level engineering trade studies, because secure-key feasibility in space is limited by single-photon detectors (SPDs) operating under SWaP, thermal, and radiation constraints. However, the question arises: does the literature provide sufficiently consistent evidence to guide detector selection for space QKD? This systematic evidence map examines how recent research connects SNSPDs, Si SPAD/APD, InGaAs SPAD/APD, and NFAD variants to CubeSat QKD and space-based quantum communication links. To do so, a concept-token methodology identifies mission contexts and detector families through targeted keywords and key phrases, followed by structured extraction of detection efficiency <i>η</i>, dark count rate (DCR), timing jitter, receiver timing window Δ<i>t</i>, operating mode, temperature/cooling, and radiation evidence. The results show an upward trend in publications, with many appearing in the last two years. SNSPDs and APD/SPAD families are most regularly discussed, yet key parameters-especially <i>η</i>, jitter, and explicit Δ<i>t</i>-are reported unevenly, limiting cross-study comparability. CubeSat-tagged studies emphasize APD/SPAD feasibility and radiation-driven DCR evolution, while SNSPDs remain performance-leading but cryogenics-limited. Standardized reporting of <i>η</i>, DCR, jitter, Δ<i>t</i>, temperature, and radiation conditions emerges as a practical avenue for accelerating deployable space-QKD receivers.