Flux quantization is a quantum phenomenom in which the magnetic field is quantized in the unit of h / 2e, also known variously as flu quanta, fluxoids, vortices or fluxons.

Flux quantization happens in several low-temperature scenarios. Most notably, in Type-II superconductors . A Type-II superconductor exhibits the formation of individual flux quanta at field above the first critical field Hc1. These flux quanta persist, increasing in number and density until, at the upper critical field Hc2, where superconductivity can no longer be sustained in the material. In the intermediate regime between Hc1 and Hc2, flux quanta are present in the superconductor and their behaviour strongly influences its dynamic and static electromagnetic properties.