I have just finished my very first quantum theory of matter course and everything we did was strictly non relativistic. No QFTs whatsoever, no creation and annihilation operators, no mention to the Dirac equation. The most relativistic thing we did was the spin orbit interaction, and even then it wasn't fully justified (the factor $ \frac{1}{2} $ popped out of nowhere and we treated everything with standard non relativistic perturbation theory). Despite that the word photon kept coming up. I know it is a strictly relativistic thing but I just care about getting an intuitive idea of what it is and not a rigorous one (I'll leave that for the future).
If I have an em field is it correct to say that the photon is spread out inside this field?
When a photon is emitted from an atom is it an electromagnetic wavepacket with a wavelength kinda constant but not really (or it wouldn't be a wavepacket but rather a monochromatic wave)? Does it make sense to calculate the amplitude of this wavepacket using $ h \nu = \text{Volume in space of the wave packet} \times \epsilon_{0} E^{2} $ (i. e equating the energy of the photon to the classical em energy)?
Is an electromagnetic wave made of a single photon what the wavefunction of a single electron is to the electron?
Suppose I have a em wave made of a single photon in a large cavity. Suppose the em wave is constant in the entire cavity. Can I localize the photon with a measurement and say "It's there, with a precision (say) + or minus .1 mm". What happens to the em field then? Does it contract to that single point (+/- .1 mm) to expand again in future times to cover the whole cavity again? Is there a way to predict this time evolution with a (relativistic) Schroedinger-like equation?