Photon only exist in Quatum Mechanics, it is the quanta of light. There is no such thing as a classical photon (classical mechanic consider light as a wave)

Originally Posted by **NicoleJS** Does the mathematics of classical or quantum mechanics apply to the original particle that is downconverted into the entangled pair? fight song lyrics- Is the original particle behaving probabilistically and the mathematics of quantum mechanics applies? |

No because there is no "classical" particle of light. That why only QM can explain how SPDC exist in the first place. All QM is probabilistic at the core.

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