The authors seem to focus on "photons per bit"... Which to me doesn't seem to be the figure of merit worth focussing on, since diffraction losses at visible light wavelengths are very small compared to radio based systems, so you will in fact be receiving a lot of photons. The noise from the sun and other light sources will be far bigger than the signal, so an extra 3dB of amplifier noise actually is a pretty small issue...
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].
Single photon detectors have existed for a long timet - though not anywhere near those speeds afaik - hence the one bit part is not particularly strange, not as long as we're talking wavelengths close to visible light.
The speed and ultra low noise seems spectacularly good, but then, if you can avoid electronics and heat+junction noise in preamp you're going to get good figures.
> Currently, even the most sophisticated free-space optical communications systems can only run at speeds of under 1 Gb/s, and require ultracold temperatures to operate.
I suspect this is dated, but i can't think who other thant he laser bounce boys would be doing that. "Free space optical communications" is doing some work there as a phrase, i wonder if that means "stuff in orbit or beyond", in which case i have less trouble with the original statement.
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[ 3.1 ms ] story [ 33.6 ms ] threadhttps://en.m.wikipedia.org/wiki/Antenna_gain-to-noise-temper...
[1] https://descanso.jpl.nasa.gov/monograph/series10/Reid_DESCAN...
[2] 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.
The speed and ultra low noise seems spectacularly good, but then, if you can avoid electronics and heat+junction noise in preamp you're going to get good figures.
I suspect this is dated, but i can't think who other thant he laser bounce boys would be doing that. "Free space optical communications" is doing some work there as a phrase, i wonder if that means "stuff in orbit or beyond", in which case i have less trouble with the original statement.