Two Simple Models Derived from a Quantum-Mechanical Particle on an Elliptical Path

We analyze two simple models derived from a quantum-mechanical particle on an elliptical path. The first Hamiltonian operator is non-Hermitian but isomorphic to an Hermitian operator. It appears to exhibit the same two-fold degeneracy as the particle on a circular path. More precisely, \({E_{n} = {n^{2}E_{1}}},{n = {1,2,\ldots}}\) (in addition to an exact eigenvalue \(E_{0} = 0\)). The second Hamiltonian operator is Hermitian and does not exhibit such degeneracy. In this case the nth excited energy level splits at the nth order of perturbation theory. Both models can be described in terms of the same point-group symmetry.