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

## TL;DR

This paper maps recent research on single-photon detectors for space-based quantum key distribution, highlighting gaps in evidence and suggesting ways to improve comparability.

## Contribution

A systematic evidence map of single-photon detectors for space QKD, identifying trends and reporting inconsistencies.

## Key findings

- Publications on space QKD detectors have increased, especially in the last two years.
- SNSPDs and APD/SPADs are most studied, but key metrics are inconsistently reported.
- CubeSat studies focus on APD/SPAD feasibility and radiation effects, while SNSPDs face cryogenic limitations.

## Abstract

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 η, dark count rate (DCR), timing jitter, receiver timing window Δt, 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 η, jitter, and explicit Δt—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 η, DCR, jitter, Δt, temperature, and radiation conditions emerges as a practical avenue for accelerating deployable space-QKD receivers.