I just studied about the QM of singlet spin pairs. I have additional questions. Neither Wikipedia, nor past threads on this forum seem to address the questions. 1) A pair of electrons forming a singlet pair A. Can the pair be split again into non-entangled electrons? If yes how; just hit it with a photon? 2) Suppose we have two singlet pairs A and B. Can they be brought together without obeying the Fermi exclusion principle? 3) Can we entangle pairs A and B into a quantum system with 4 electrons and 16 spin states?