of the quantum numbers of the upper loop $n _{u}$ and the lower loop $n _{d}$ according to (6). Therefore the voltage measured on DDCI average in the time $\overline{V} = \Theta ^{-1}\int _{\Theta} dt V(t) \approx V _{min}P(n _{u} =0) + V _{max}P(n _{u} =1)$ should change from the minimum value $\overline{V} \approx V _{min}$ to the maximum value $\overline{V} \approx V_{max}$ in the narrow interval $\Delta \Phi \approx \Phi _{0}/\epsilon \ll \Phi _{0}/2$ at $\epsilon \gg 1$ when $n _{d} = 0$ and the quantum number of the upper loop takes two values $n _{u} = 0$ and $n _{u} = 1$ due to the switching of a segment of this loop in normal state by the short pulses of an external current $I_{sw}$ with the amplitude exceeding the critical current $I_{c}$ of the superconducting strip.](Fig1)

The quantum number of the continuous superconducting loop, in contrast to the flux qubit [@Tanaka04], can change only if it or its segment is switched in normal state for a while [@PRB2014C]. The numerous measurements of the critical current [@PCJETP07; @APL2016; @JETP07J] and other parameters [@PCScien07; @PLA2012] testify that the loop comes back in the superconducting state with the quantum number $n$ 