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How Physicists Create Single Photons

Quantum physicist Peter Mosley explains in the latest 100 Second Science video.
Image: sun/Flickr

A single photon is about the "smallest" thing one might ever conceive of, at least in that it doesn't really occupy geometric space in a recognizable sense. There's no mass to a photon so how can we say there's any thing to a photon? Still, we usually say a photon is a particle, which implies a point-like something (a thingy-ness), but it's also a space or a region, a more ethereal-seeming zone of photon possibilities. But if we define a photon as a boundary around some space within which a photon will begin to "push back" then we can say it's .5 x 10-15 meters, which is about the smallest thing that ever can be (even though it's not really a thing).

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And yet physicists have ways of creating photons on an individual basis. Which is amazing.

How do they do this? I'll let quantum optics researcher Peter Mosley explain, courtesy of the latest of Physics World's 100 Second Science explainers.