Perturbative QED
A full lecture reconstruction introducing perturbative quantum electrodynamics from the Coulomb-gauge Hamiltonian, identifying the fine-structure constant as the small expansion parameter, and using time-independent perturbation theory to analyze the QED vacuum and one-electron states.
Introduction
At this point in the course, the full Hamiltonian structure of quantum electrodynamics is finally on the table.
We have: - a free photon field, - a free Dirac field, - and interaction terms coupling light and charged matter.
That means, in a very real sense, we have arrived at the complete theory of QED.
A full lecture reconstruction showing how the free electromagnetic field in Coulomb gauge becomes an infinite set of quantum harmonic oscillators whose quanta are photons, and why gauge-invariant observables still preserve relativistic causality in photon detection.
A full lecture reconstruction showing why naive low-order perturbative QED corrections to particle energies are problematic, why Compton scattering is the first clean finite order-α process, and how Lorentz-invariant scattering amplitudes emerge only after coherent addition of all electron and positron intermediate-state processes.