Electronics with superconducting junctions

Josephson tunneling, an effect predicted and discovered within the last decade, has already formed the basis of a new technology. The “Josephson devices” are ultrasensitive electronic measuring devices that operate at liquid-helium temperatures (1–4K) and exploit the macroscopic-scale quantum properties of superconducting junctions. They have been used to measure, for example, smaller low-frequency voltages and magnetic fields than can be measured with any other methods, and are also being investigated as possible high-frequency detectors and mixers, as thermometers and as computer elements. One of the most important applications of the Josephson effect has been in the precision measurement of e/h in an experiment that avoids any assumptions from quantum electrodynamics (QED); results from this experiment give a convenient and accurate way to express the standard of electromotive force.