Optimal topological test for degeneracies of real Hamiltonians.
We consider adiabatic transport of eigenstates of real Hamiltonians around loops in parameter space. It is demonstrated that loops that map to nontrivial loops in the space of eigenbases must encircle degeneracies. Examples from Jahn-Teller theory are presented to illustrate the test. We show furthermore that the proposed test is optimal.
Department of Quantum Chemistry, Uppsala University, Box 518, S-751 20 Sweden.
Niklas
N
Johansson
Erik
E
Sjöqvist