Demonstration of the magnetic flux quantum using one of the new high-temperature superconductors - yttrium- barium-copper oxide (Y-Ba2-Cu3-O7-x). The graph is a dramatic example of quantum mechanics at work on a macroscopic scale. It shows that the magnetic flux enclosed by a ring of superconductor is quantised in units of the fundamental constants h/2e. Each level corresponds to a different number of wavelengths of the superconducting wave- function round the ring. Discovered in 1986, the new superconducting ceramic materials are expected to lead to a technological revolution & are the subject of intensive worldwide research.