Lez #23+24 Radiation - matter, rabi oscillations, perturbative expansion

 Today we recalled the basic concepts of quantum mechanics, introducing the density matrix. We stressed the importance  of density matrix to describe statistical mixtures, and how this is not possible through an eigenstates superposition (for instance a two level system).

We discussed how to solve Bloch equation and Rabi oscillation, introducing the rotating wave approximation to neglect some terms in the integration.

We then introduced Shroedinger, Heisenberg and Interaction schemes (in this latter both eigenfunctions and operators evolve, and the temporal evolution related to the unperturbed Hamiltonian is removed from the wavefunction). Then it makes sense a perturbative expansion of the eigenfunctions and of the density matrix in the Interactions scheme. Finally, we went back to the Shroedinger scheme.

Please refer to the first part of the notes added to classroom.