Quantum Mechanics: Semiclassical Approximation

This lecture covers the Bohr-Sommerfeld quantization method and the distinction between perturbative and non-perturbative effects in quantum mechanics. The instructor discusses the semiclassical approximation for K(E; x, y) and the computation using saddle points, emphasizing the importance of considering non-perturbative effects that perturbation theory may miss. Examples of meta-stable states and the double well potential are used to illustrate the limitations of perturbative approaches and the significance of non-perturbative effects. The lecture concludes with a discussion on instantons and the euclidean propagator in quantum mechanics.