Subtract one Photon, get more photons. More Quantum weirdness.

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It says at one point that in some circumstances, if you remove a photon from a stream of light, the stream afterwards tends to have more photons in it.

I am just wondering whether some of those here knowledgable about physics might be able to explain how this works.

The only way I can account for this intuitively (always a mistake, I know, but one can hardly help it) is to think that the rest of the photons in the stream somehow “split” into lower energy photons or something.


I can’t get into the article to read it, so I can’t comment knowledgeably. The chief author is one of my old professors, who’s been working on dramatically slowed light for the past few years, so it might be related to those experiments. As even his title for it emphasizes the weirdness, this is evidently some new and unexpected wrinkle, but I’ll have to wait to see it.
That said, the laws of physics presumably still hold, and that includes the conservation of energy and momentum, both carried by photons. You can’t just pull out one photon and have more appear with no change in energy unless it;s coming from someplace. And I’ll note, for kicks, that there already are processes in which the number of photons change – stimulated emission, for instance, where you pull energy out of an excited system to get that extra photon, or nonlinear nth harmonic generation, where you split one photon into two or more photons.

Boyd was one of your professors? Cool. While I think his nonlinear book could use a good re-write, I think it is still the best one out there.

Energy and momentum must be conserved, but that does not mean that photons must be conserved. There is no quantum number for “photon number”, the same way there is for (say) baryon number. In fact, the number of photons in a system can even depend on the reference frame in which you’re observing a system.

Which doesn’t shed much light on the mechanism here (I haven’t read the article yet), but it certainly makes it look plausible.

As, indeed, I said later in that post.

Apparently you need to shed even less light, thus providing more.