Bonnes fetes de Noel. When an excited electron returns to its ground state a photon is emitted. Suppose that the electron's spin skip from +1/2 to -1/2 (around z)and that the photon has a momentum parallel to z. I suppose that this photon has a circular polarization around z (Is it true?) The problem is that there is no spin alone conservation but total angular momentum conservation. Knowing all about |e> and |g> what can we calculate about the polarization of the emitted photon? Have you links?