SQUID

A Simple QUantum Interference Device is loop of superconductor that contains one or more Josephson Junctions. They can be used as very sensitive magnetometers, and form the basic building block of several sorts of logic device.

The basic principle of operation is closely linked to flux quantisation. This is the phenomenon that the favoured states for a loop of superconductor are those where the flux inside is a multiple of the flux quantum.