Multiple and single measurements of a mesoscopic quantum system with two   permitted states
  Mesoscopic loop is proposed in many works as possible solid-state quantum bit, i.e. two-state quantum system. The quantum oscillations of resistance and of rectified voltage observed on asymmetric superconducting loops give evidence of the two states at magnetic flux divisible by half of the flux quantum. But our measurements of quantum oscillations of the critical current of these loops have given results coming into irreconcilable contradictions with result of the observations of the quantum oscillations of resistance. 
A.A. Burlakov, V.L. Gurtovoi, S.V. Dubonos, A.V. Nikulov and V.A.   Tulin