Loved this article! I initially was confused by how this transition would work with the conservation of angular momentum (since the electron would be flipping from spin ±½ to the opposite one). But then remembered that photons are spin 1 particles, so the math works out. Neat.

that's not right. if photons were truly spin 1, there would be 3 spin eigenstates available, but in fact there are only 2 (Sz=0 is unavailable). the pithy argument invokes the absence of a stationary frame of reference. for all practical purposes, photons are behave like spin 1/2 particles (despite being bosons). see, for example, the jones algebra / calculus.