When is a single photon not a single photon?

Beamsplitters like these are enough to confirm that single photons can be linearly polarized.

Fermilab

One of the joys of the arXiv is that anyone can submit anything to the website. Cranks and kooks can publish to their hearts' content in the theoretical physics section. Their work will remain there, read only by those searching for casual amusement. Yet somewhere between all the excellent science and slapstick comedy are scientists who just get stuff flat out wrong.

This is the story of how two respected physicists failed to understand photon angular momentum. Don't worry, they're not alone. Every physicist who has given the subject any thought has lost sleep working it out (and has had nightmares involving Jackson's Classical Electrodynamics). Since I lost sleep over it, I figured I would ensure that you all lose some sleep too.

Spinning photons and rotating electric fields

The fundamental confusion arises from the fact that there are two equivalent ways of describing the angular momentum of a photon. A cursory inspection of nature, however, seems to reveal that one is more natural than the other.