The Josephson effect describes a supercurrent flowing through a thin insulating barrier between two superconductors.
Brian Josephson predicted the effect in 1962 while he was a graduate student at the University of Cambridge. Cooper pairs can tunnel across the barrier, creating a current even when no voltage is applied. An applied voltage causes the current to oscillate at a precisely related frequency.
The arrangement is called a Josephson junction. It is used in superconducting quantum computers, extremely sensitive magnetometers called SQUIDs, and voltage standards. The effect demonstrates macroscopic quantum coherence because the current depends on the relative phase of the superconducting states.
The Josephson effect is different from the Meissner effect. The Meissner effect is the expulsion of magnetic fields from a superconductor, whereas Josephson behavior concerns coherent tunnelling across a junction.