Parent Photon Split into Two Daughter Photons

When the down-conversion crystal splits the high energy blue parent photon into two lower energy daughter photons, these photons become entangled in energy. The two daughter photons can have the same energy or one can be stronger than the other, or any other combination. But because they are entangled the combined energy of the two daughter photons always exactly equals the energy of the parent photon. These photons are also in a superposition state. Although the total energy of the daughters must add up to the energy of the parent the energies each photon is undefined. They do not have individual values. Instead they are simultaneously every possible combination that makes up the energy of the parent photon.