The Hamiltonian of Quantum Electrodynamics
The purpose of these lectures in to establish a bridge between the full, relativistic QED and its nonrelativistic approximation, used in quantum optics and atomic physics. Usually, one introduces the nonrelativistic QED by minimally coupling the quantized electromagnetic field to the quantum-mechanical particle (or particles). Such a procedure, certainly, leads most directly to the final result, but it has two shortcomings. First, it does not directly generalize to an improved theory, in which the lowest order relativistic correcions are included. Second, it does not explain what is the connection between the fundamental theory of relativistic QED and its less sophisticated counterpart—the nonrelativistic QED.
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