2 ms·

To be fair, technically optical interference is a quantum phenomenon, it's just we've known about it for a long while since photons in the radio and visible lig

To be fair, technically optical interference is a quantum phenomenon, it's just we've known about it for a long while since photons in the radio and visible light end of the spectrum is toward the wave-like side of the wave/particle duality and we've been modelling it as entirely a wave as a result. Although describing it as a "quantum phenomenon" does admittedly dress it up to be far more exotic than it is, since it's an effect that appears in all waves.

abdullahkhalids 3y ago
There is a very specific metric that is used to distinguish whether a beam of light/EM wave is "classical" or "quantum". The metric is called the second order correlation function, labelled g^(2). If a EM wave has g^(2)>1 then experiments that demonstrate quantum phenomena cannot be successfully performed with this wave. Hence, the EM wave is called classical. Only if g^(2) < 1 can you start doing quantum stuff with it. In this case, almost certainly the waves have g^(2) > 1.
- marginalia_nu 3y ago
  Coherence is a function of time/length though. At a sufficiently short time interval, all waves are coherent. It's effectively a measure of the time (or equivalently distance) between phase shifts. Since they're claiming to use interference, which only exists in coherent waves, I think it's safe to say in g(2)<1 for the scale they're utilizing interference at. Coherence is so inexorably linked to interference, it's measured using an interferometer.
  - abdullahkhalids 3y ago
    Simple water waves or simple sinusoidal EM wave (such as AM radio waves) display interference. Both are classical objects because their g^(2) > 1. You can look at, for instance, the g^(1) function to determine how nicely a particular wave interferes with itself. Second order correlations directly test for the bosonic nature of photons. In quantum light, photons clump together because they are bosons, while in classical light photons are independent of each other and any clumping that happens is purely probabilistic. The g^(2) function tests this degree of clumping.

abdullahkhalids 3y ago

There is a very specific metric that is used to distinguish whether a beam of light/EM wave is "classical" or "quantum". The metric is called the second order correlation function, labelled g^(2). If a EM wave has g^(2)>1 then experiments that demonstrate quantum phenomena cannot be successfully performed with this wave. Hence, the EM wave is called classical. Only if g^(2) < 1 can you start doing quantum stuff with it. In this case, almost certainly the waves have g^(2) > 1.

marginalia_nu 3y ago
Coherence is a function of time/length though. At a sufficiently short time interval, all waves are coherent. It's effectively a measure of the time (or equivalently distance) between phase shifts. Since they're claiming to use interference, which only exists in coherent waves, I think it's safe to say in g(2)<1 for the scale they're utilizing interference at. Coherence is so inexorably linked to interference, it's measured using an interferometer.
- abdullahkhalids 3y ago
  Simple water waves or simple sinusoidal EM wave (such as AM radio waves) display interference. Both are classical objects because their g^(2) > 1. You can look at, for instance, the g^(1) function to determine how nicely a particular wave interferes with itself. Second order correlations directly test for the bosonic nature of photons. In quantum light, photons clump together because they are bosons, while in classical light photons are independent of each other and any clumping that happens is purely probabilistic. The g^(2) function tests this degree of clumping.