NB that CMOS and CCD sensors might have a QE approaching 1, but they cannot (yet) be used to detect a single photon due to internal noise (unless you get a real

NB that CMOS and CCD sensors might have a QE approaching 1, but they cannot (yet) be used to detect a single photon due to internal noise (unless you get a really expensive sensor and make it super cold). For detecting single photons, you need really high in-sensor amplification. Options include SPADs or photomultipliers if you don't need an image, or image intensifier tubes (used in night vision) if you do need an image. Semiconductor cameras that use IIT-like operational principles are in development now, undergoing testing for next-gen (digital) night vision.