superconductivity was discovered by H. Kammerlingh Onnes in 1911. Studying metals at low temperatures, he noticed that the resistance of mercury suddenly dropped to zero below a certain temperature. He reported: ”Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state“.
A superconductor conducts electricity without resistance. Zero. This unique quantum state is accompanied by even more unusual properties such as expulsion of external magnetic fields (Meissner Effect) and flux pinning (pinning of magnetic field strands or fluxons). The latter is the origin of the Quantum Locking effect.
Fluxons. Superconductivity and magnetic fields do not 'like' each other. When possible, the superconductor will expel all magnetic fields from inside. This is the Meissner effect. In our case, since the superconductor is extremely thin, the magnetic field DOES penetrate. However, it does so in discrete quantities (this is quantum physics after all! ) called Fluxons.
Quantum Locking. Inside each magnetic flux tube superconductivity is locally destroyed. The superconductor will try to keep the magnetic tubes pinned in weak areas (e.g. grain boundaries). Any spatial movement of the superconductor will cause the flux tubes to move. In order to prevent that the superconductor remains “locked” in midair. For more details see here.