A Josephson junction is a type of electronic circuit capable of switching at very high speeds when operated at temperatures approaching absolute zero. Named for the British physicist who designed it, a Josephson junction exploits the phenomenon of superconductivity, the ability of certain materials to conduct electric current with practically zero resistance. Josephson junctions are used in certain specialized instruments such as highly-sensitive microwave detectors, magnetometers, and QUIDs.
A Josephson junction is made up of two superconductors, separated by a nonsuperconducting layer so thin that electrons can cross through the insulating barrier. The flow of current between the superconductors in the absence of an applied voltage is called a Josephson current, and the movement of electrons across the barrier is known as Josephson tunneling. Two or more junctions joined by superconducting paths form what is called a Josephson interferometer.
While researching superconductivity, Brian David Josephson studied the properties of a junction between two superconductors. Following up on earlier work by Leo Esaki and Ivar Giaever, he demonstrated that in a situation when there is electron flow between two superconductors through an insulating layer (in the absence of an applied voltage), and a voltage is applied, the current stops flowing and oscillates at a high frequency.
The Josephson effect is influenced by magnetic fields in the vicinity, a capacity that enables the Josephson junction to be used in devices that measure extremely weak magnetic fields, such as superconducting quantum interference devices (SQUIDs). For their efforts, Josephson, Esaki, and Giaever shared the Nobel Prize for Physics in 1973.