It applies to photons and electrons: when superposition consists of valid solutions of the schrodinger equation, these components evolve independently as if the

It applies to photons and electrons: when superposition consists of valid solutions of the schrodinger equation, these components evolve independently as if the other components didn't exist. It's possible to measure them in a rotated basis because a single elementary particle doesn't have inner structure. If you want to analyze the structure, you will have difficulty measuring in a rotated basis, this starts with two particles.