Josephson effect

The Josephson effect is the coherent flow of Cooper pairs between superconductors separated by a thin barrier. A constant voltage across the barrier makes the supercurrent oscillate at a frequency proportional to voltage.

Josephson junction: A device made from two superconductors separated by a thin, nonsuperconducting barrier. It is the structure through which the effect occurs.
Josephson voltage standard: A voltage reference based on quantized voltage steps in microwave-driven Josephson junctions. The AC effect converts frequency standards into precisely known voltages.
Brian Josephson: A British physicist who predicted coherent tunneling between superconductors in 1962. His prediction gave the effect its name.
Quasiparticle tunneling: The tunneling of individual excitations across a barrier in a superconducting junction. Unlike the Josephson current, it carries dissipative current through excited states.
Josephson relations: Equations relating a junction’s supercurrent to phase difference and the phase’s time evolution to voltage. They quantify both the direct and voltage-driven forms of the effect.
SQUID: A superconducting loop containing Josephson junctions, used to measure extremely small magnetic fluxes. Junction currents make the loop’s response sensitive to magnetic flux.
Superconductivity: A state of matter with zero electrical resistance and expulsion of magnetic fields below a critical temperature. The effect arises from coherent superconducting states on both sides of the barrier.
Ohm's law: The relation stating that current through an ohmic conductor is proportional to voltage. A Josephson junction can carry supercurrent at zero voltage, unlike an ordinary resistor.
Superconducting phase: The quantum-mechanical phase of the superconducting order parameter. Its difference across the barrier sets the supercurrent.
Josephson junction array: A series or network of Josephson junctions whose collective behavior produces useful electrical responses. Arrays combine junctions to generate practical voltage standards.

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