[Green_man]

many properties of photons are quantum in nature, relying on an underlying continuous wave function, that when "measured", will output some discrete value. The wave function determines the likelihood of each possible measurement value, with the relationship amplitude^2 = probability.

I was similarly confused about which property of the photons they were measuring, it seemed they might be measuring the number of photons over specific periods of time. Because the position of each individual photon is uncertain until it is destructively measured, randomness will be generated by the "collapse" of the wave function, where one of the possible outputs is generated. Before measuring, photons can be in a "superposition" of bouncing inside the bow tie shaped chamber, or escaping out of the laser to be measured. After measuring, a photon can either be inside the laser, or outside the laser, but not the "both" of a previous superposition. Arguably, superposition isn't really a "both", but there aren't great words in English for this unfortunately. The fundamental uncertainty of measuring a superposed quantum state has been convincingly demonstrated in experimentation, but nobody really knows _why_ it happens this way. The "measurement problem" has inspired many interpretations of quantum mechanics, but many of them are unfalsifiable.

https://en.wikipedia.org/wiki/Measurement_problem