the necessary Josephson junctions $J _{a}$, $J _{b}$ and two unnecessary Josephson junctions $J _{l}$, $J _{r}$ created because of our technology. Two current-voltage characteristics, shown in Fig. 4, measured at different value of magnetic field correspond to even and odd sum $n _{u} + n _{d}$.

In summary we propose a new type of magnetometer, the DDCI, and present experimental evidence of its opportunity. The DDCI can reach sensitivities better than $20 \ mV/\Phi _{0}$, which exceeds that of dc SQUID by more than one order of magnitude. The effect is due to the strong discreteness of the energy spectrum of the continuous superconducting loop. The advantage of DDCI lies also in circuitry, as one does not need to couple the device to a flux transformer for the measurement of small magnetic fields. The flux transformer is used for the measurement of tiny magnetic fields $B = \Phi /S$ since the area $S$ of the dc SQUID cannot be too large because of the strong screening $\Phi _{I} = LI _{c,j}> \Phi _{0}/2$ and $\beta = 2L I _{c,j}/\Phi _{0} > 1$ in the loop with a high magnetic inductance $L \approx \mu _{0}l$ [@SQUID1977]. In the DDCI the 