dw \approx 12000 \ nm^{2}$ corresponds to $\lambda _{L}^{2}(T) = \lambda _{L}^{2}(0)(1 - T/ T _{c})^{-1}$ of aluminium with its London penetration depth $\lambda _{L}(0) \approx 50 \ nm$ at $T \approx 0.8T _{c}$. The critical temperature of aluminium loops was $T _{c} \approx 1.3 \ K$.

![\[fig:epsart\] The real structure used for the observation of the voltage jumps with the change of the quantum numbers of its two loops weakly connected by two Josephson junctions $J _{a}$ and $J _{b}$. The two aluminium loops are shifted with respect to each other because of the simple technology of two-angle evaporation used in our work. The structure has two unnecessary Josephson junctions $J _{l}$ and $J _{r}$ because of this technology. Photo of 4 $\mu m $ aluminium loops is shown.](Fig2)

The structure, shown on Fig.2, without the additional current leads $cl$, Fig.1, cannot be used as a sensitive magnetometer because the quantum number $n _{u}$ of the continuous superconducting loop may not meet the minimum kinetic energy (2) when no segment is switched in the normal state. We use this structure only for the observation of the voltage jump due to the change of the quantum number. This change takes 