magnetic flux induced by the persistent current does not depend on the loop size $l$ since $\Phi _{I} = LI _{p} = (L/L _{k})(n\Phi_{0} - \Phi) \approx (s/\lambda _{L}^{2}(T))(n\Phi_{0} - \Phi)$ [@QuSMF2016].

This work has been supported by the Russian Science Foundation, Grant No. 16-12-00070.

**Supporting Information** 
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Strong discreteness of the energy spectrum of continuous superconducting loop
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Niels Bohr postulated as far back as 1913 a strong discreteness of the energy spectrum of atoms. According to Bohr’s condition $pr = n\hbar $, that the angular momentum $pr$ is an integer multiple of Planck’s constant $\hbar = h/2\pi $, the energy discreteness $E_{n+1} - E_{n} = p_{n+1}^{2}/2m - p_{n}^{2}/2m = (2n+1)\hbar ^{2}/2mr^{2}$ decreases with the increase of the orbit radius $r$. The energy spectrum of atom is strongly discrete due to small radius of electron orbits: the energy difference between adjacent permitted states $\Delta E \approx \hbar ^{2}/2mr^{2} \approx 2 \ 10^{-18} \ J$ for the Bohr radius $r_{B} \approx 0.05 \ nm = 5 \ 10^{-11} \ m$ corresponds to the temperature $T = \Delta E/k _{B} \approx 100000 \ K$. The discreteness decreases down to $\Delta E \approx \hbar ^{2}/2mr^{2} \approx 2 \ 10^{-18} \ J$ corresponding 