Could two degenerate energy states be observed for a superconducting   ring at $\Phi_{0}$/2?
  The Little-Parks oscillations of the resistance and the quantum oscillations of the rectified voltage observed for asymmetric superconducting Al rings give experimental evidence of two degenerate energy states at the magnetic flux $\Phi_{0}$/2. The quantum oscillations of the critical current as a function of magnetic field have also been measured. On the one hand, these oscillations confirm that the quantum oscillations of the rectified voltage are a consequence of periodical dependence of the asymmetry of the current-voltage curves and, on the other hand, comparison of the oscillations with Little-Parks measurements results in contradiction. 
A.A. Burlakov, V.L. Gurtovoi, S.V. Dubonos, A.V. Nikulov, and V.A.   Tulin