all $N _{s}$ pairs equals $M _{p} = \oint _{l} dl sr\Psi ^{*}\hat{p} \Psi = \oint _{l} dl sr\Psi ^{*} (-i\hbar \nabla )\Psi = sr|\Psi |^{2}\hbar \oint _{l} dl \nabla \varphi  =  N _{s}\hbar n $.

![\[fig:epsart\] The picture on the left: The virgin magnetization $\Delta M \propto L_{f}I _{p}$ of aluminum ring with the radius $r \approx 1 \ \mu m$ increases up to $|v| \approx  v _{c} $ with the magnetic flux $\Phi \approx BS$. The quantum number changes from $n = 0$ to $n = 1$ $|\Phi /\Phi _{0}| \approx 1.7 \approx  r/\surd 3 \xi (T)$, $n = 1$ to $n = 2$ $|\Phi /\Phi _{0}| \approx 1.7 + 1 = 2.7$, $n = 2$ to $n = 3$ $|\Phi /\Phi _{0}| \approx 1.7 + 2 = 3.7$. The drawing at the upper right: The velocity of Cooper pairs changes by jump at a definite magnetic flux $\Phi = (n+0.5) \Phi _{0}$ due to the switching of ring segment in the normal state for a while by an external current, a noise or thermal fluctuations, or due to quantum fluctuations. The two states $n$ and $n+1$ have the opposite velocity $v$ and equal kinetic energy $E _{k} 