It really is a QRNG, but the only "quantum" thing you need to know is that light arrives in lumps.
As nabla9 points out, they are really measuring the shot noise. The fundamental assumptions of shot noise are that you have distinct items arriving at an average rate, and that the probability of a single item arriving in an interval dt is proportional to the length of the interval dt. Since light arrives in quantized lumps, and you expect an avg number of lumps that increases linearly with collection time, there is shot noise associated with it. It could describe the arrival of buses, which also happen to arrive in quantized lumps, if you could somehow convince the drivers to increase your probability of being picked up proportionally to how long you wait at the bus stop.
It's a nice enough hack, but the medium article is overselling "probabilistic nature of quantum mechanics to produce a sequence of entirely random digits." The arxiv paper is clearer and is much less of a sales job.
FWIW, the tough thing here is the nature of shot noise: In some interval of time, the expectation value from a constant power of light is N photons in a single pixel. The RMS deviation over a series of trials is sqrt(N). So the phone needs to measure sqrt(N)/N accurately enough to pull out random digits. The ratio sqrt(N)/N implies that you wish to measure low N, or low numbers of photons. That a cell phone has such sensitivity is the key observation. I expected the paper to have a plot of RMS(photons) vs LED output power to show definitively that the noise is photon-induced shot noise (there are other sources), but it is a nice paper nonetheless.
It really is a QRNG, but the only "quantum" thing you need to know is that light arrives in lumps.
As nabla9 points out, they are really measuring the shot noise. The fundamental assumptions of shot noise are that you have distinct items arriving at an average rate, and that the probability of a single item arriving in an interval dt is proportional to the length of the interval dt. Since light arrives in quantized lumps, and you expect an avg number of lumps that increases linearly with collection time, there is shot noise associated with it. It could describe the arrival of buses, which also happen to arrive in quantized lumps, if you could somehow convince the drivers to increase your probability of being picked up proportionally to how long you wait at the bus stop.
It's a nice enough hack, but the medium article is overselling "probabilistic nature of quantum mechanics to produce a sequence of entirely random digits." The arxiv paper is clearer and is much less of a sales job.
FWIW, the tough thing here is the nature of shot noise: In some interval of time, the expectation value from a constant power of light is N photons in a single pixel. The RMS deviation over a series of trials is sqrt(N). So the phone needs to measure sqrt(N)/N accurately enough to pull out random digits. The ratio sqrt(N)/N implies that you wish to measure low N, or low numbers of photons. That a cell phone has such sensitivity is the key observation. I expected the paper to have a plot of RMS(photons) vs LED output power to show definitively that the noise is photon-induced shot noise (there are other sources), but it is a nice paper nonetheless.