I consistently had this question of how could the light-matter interaction be described in terms of the fundamental language of QED. To be more specific, is there a way to 'derive' the interaction Hamiltonian such as Jaynnes-Cummings Hamiltonian from the fundamental interaction Lagrangian such as
$$\mathcal{L}=i\overline{\psi}\gamma^{\mu}(\partial_{\mu}-ieA_{\mu})\psi-m\overline{\psi}\psi-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}.$$
used nearly exclusively in the particle physics context to describe electron photon interaction?
I found a similar question raised in
What is the difference between QED and quantum optics?
but the answer to the question only stated that full quantum field theoretic description is rarely used and semiclassical description suffices and is convenient in most cases.