Topic summary
Magnetic flux quantum
The magnetic flux through some contour is defined as the magnetic field multiplied by the loop area. In some physical systems, such as in superconductors, the magnetic flux can only take certain fixed (or, quantized) values. The values allowed to be taken by the magnetic flux are integer multiples of the magnetic flux quantum. This restriction on the values of the magnetic flux is called magnetic flux quantization.
The quantization of the magnetic flux originates from the requirement that the wave function describing a particle must be single-valued. Because a magnetic field induces a phase shift in the wave function when integrating on a closed contour, the wave function can only remain single-valued if the magnetic flux takes on a quantized value for which the phase shift is equal to .
The phenomenon of flux quantization was predicted first by Fritz London then within the Aharonov–Bohm effect and later discovered experimentally in superconductors.