Intersections of energy surfaces in quantized Sinai billiards

Degeneracies in the spectra of quantized Sinai billiards are numerically investigated. Two effects recently predicted are observed, namely, (i) a geometric phase of nπ during a circuit surrounding n conical intersections and (ii) neighboring glancing and conical intersections. Experiments in isomorphic flat microwave resonators exhibit excellent agreement with computed eigenvalues and eigenfunctions.