I read it some where that there is very small decoherence for photons. The reason being that photons do not interact with each other (Is that because photons are chargeless, colorless and flavourless particles?) and hence the information that they contain tends to stay with them. They have a small cross-section. However if you consider the compton scattering, there the photon is interacting. Secondly, in vacuum, a photon interacts with the quantum fluctuations, right? So how is it that there is little or no decoherence for photons?