6 Quantum mechanics in three dimensions

Finally, we will move on and discuss quantum systems in three dimensions, since

we (probably) live in a three-dimensional world. These problems are usually

substantially more difficult, since we have to deal with partial derivatives. Also,

unlike the case of one dimension, we will run into degenerate states, where

multiple eigenstates have the same energy. We thus have to find some other

observables (that commute with the Hamiltonian) in order to fully classify the

eigenstates.