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 equivalent to an Hermitian operator. It appears to exhibit the same two-fold degeneracy as the particle on a circular path. More precisely, the spectrum is $E_n=n^2{E}_1,n=0,\pm 1,\pm 2,\dots$, $E_1>0$. 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 symmetry point groups with one-dimensional irreducible representations.