# Hydrogen transition and photon behavior

consider a transition for an electron in the Hydrogen atom from the ground state to the 1st excited state. Let's say this transition occurs through absorption of a photon of exactly the energy required to excite the electron.

what happens to the photon right after it is absorbed? is it annhilated when it is absorbed? does its wavefunction cease to exist? I'm curious about this process thanks.

Each state can also be described with "occupation numbers" $n_i (t)$. Physical processes are redistributions of the occupation numbers. Transition from $n_{ph} = 1$ to $n_{ph} = 0$ is absorption of a photon but not a photon wave function destruction.