corresponding to the minimal kinetic energy (2) at the $(n-0.5)\Phi _{0} < \Phi < (n+0.5) \Phi _{0}$ with the predominant probability $P(n) \approx 1$.The probability $P(n)$ of the $n$ state should change in a narrow interval of magnetic flux $\Delta \Phi \approx  \Phi _{0}/\epsilon $ near $\Phi = (n+0.5) \Phi _{0} $ when a segment of the continuous superconducting loop is switched in the normal state by the short pulses of an external current $I_{sw}$ with a frequency $f$. Such switching may be provided with the help of the additional current leads shown on Fig.1. The quantum number $\overline{n} = \Theta ^{-1}\int _{\Theta} dt n(t)$ average in a time $\Theta \gg 1/f$ equal $\overline{n} \approx nP(n) + (n+1)P(n+1)$ should change in this narrow interval $\Delta \Phi \approx \Phi _{0}/\epsilon \ll \Phi _{0}/2$ from $n$ to $n+1$. We propose to use the differential double contour interferometer, shown on Fig.1, in order to transform the $\overline{n}$ variation in the variation of the voltage average in the time $\overline{V} = \Theta ^{-1}\int _{\Theta} dt V(t)$ in the same narrow interval $\Delta \Phi \ll \Phi _{0}/2$. It may be possible due to the jump of the critical current of the DDCI with the change 