= Magnetic flux quantum
{tag=Physical Review Letters article}
{wiki}
TODO is there any relationship between this and the <Josephson effect>?
Experimental observation published as <Experimental Evidence for Quantized Flux in Superconducting Cylinders>.
This appears to happen to any superconducting loop, because the superconducting wave function has to be continuous.
<video Superconducting Qubit by NTT SCL (2015)> suggests that anything in between gets cancelled out by a <superposition> of current in both directions.