L9.1 The interaction picture and time evolution
PROFESSOR: We're finished with WKB. In recitation, you saw some transmission across the barrier and that's also included in the notes. That's an important application of WKB and should look at it. And today we're going to start with a new topic. It's time-dependent perturbation theory. And time-dependent perturbation theory is going to keep us busy for a number of lectures. There's a lot of applications of these ideas and the methods are rather general. Here is the place where we will learn about Fermi's Golden Rule. The kind of rule that is useful for radiation problems, ionization problems, transitions. It's all very applied. Nevertheless, we have to develop the theory carefully and see what are the main concepts. So time-dependent perturbation theory is our subject. Time-dependent perturbation theory. Again, we will begin with a Hamiltonian that is time independent. And we know about it. We call this Hamiltonian H zero. The same name we ...