They use an amplifier to turn the one photon into many photons before the signal gets to the detector. For microwave, (current state of the art) they use a r

They use an amplifier to turn the one photon into many photons before the signal gets to the detector. For microwave, (current state of the art) they use a ruby maser[1]. In this scheme they use a Phase-sensitive fiber-optic amplifier[2]. [1] https://descanso.jpl.nasa.gov/monograph/series10/Reid_DESCANSO_sml-110804.pdf https://descanso.jpl.nasa.gov/monograph/series10/Reid_DESCAN... [2] https://www.laserfocusworld.com/fiber-optics/article/16548079/optical-amplifiers-phasesensitive-fiberoptic-amplifier-has-recordlow-11-db-noise https://www.laserfocusworld.com/fiber-optics/article/1654807... Edit: You can tell this stuff is black magic because it involves rare gems and cauldrons of liquid helium boiling off clouds of sinister vapors.