region may be very narrow due to a big value $\epsilon = I _{p,A}\Phi _{0}/k _{B}T \gg 1$ equal, for example $\epsilon \approx 1500$ at the temperature of measurement $T  \approx 1 \ K$ and a typical value $I _{p,A} = 10 \ \mu A$ measured, for example in [@PCJETP07]. Measurements [@Tanaka04] of flux qubit (superconducting loop with three Josephson junctions) corroborate the change of the probability $P(n) $ in a narrow region of magnetic flux predicted by the relation (3). For example the probability changes from $P(n) \approx 1$ to $P(n) \approx 0$ in a region from $\delta \Phi \approx  -0.002\Phi _{0}$ to $\delta \Phi \approx  0.002\Phi _{0}$ at the temperature of measurement $T  \approx 0.1 \ K$, see Fig.5 of [@Tanaka04], and the value $I _{p,A} < 0.6 \mu A$ of the flux qubit measured in [@Tanaka04].

![\[fig:epsart\] The work principle of the superconducting differential double contour interferometer (DDCI). A bias current $I$ flows from the upper loop to the lower loop through two Josephson junctions $J _{a}$ and $J _{b}$ (labeled with white circles). The maximum value of the superconducting current through these Josephson junctions should depend on parity of the sum $n _{u} + n _{d}$ 