Josephson junction

Josephson junctions, first postulated by B. D. Josephson and first made by John Rowell and Philip Anderson, are

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quantum-mechanical circuit

Related Topics:
Quantum-mechanical - Circuit

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elements of superconducting devices. They are

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most commonly used in SQUIDs and Rapid Single Flux Quantum integrated circuits.

Related Topics:
SQUIDs - Rapid Single Flux Quantum

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A Josephson junction is the interface between two

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superconducting materials separated by a

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non-superconducting barrier. A current may flow freely within the

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superconductors, but the barrier prevents the current from flowing

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freely between them. However, the supercurrent may tunnel through the

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barrier, depending on the quantum phase of the superconductors. The amount of supercurrent that may tunnel through the

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barrier is restricted by the size and substance of the barrier. The

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maximum value the supercurrent may attain is called the critical current

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of the Josephson junction, and is an important phenomenological

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parameter of a junction.

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Josephson junctions have two basic electrical properties. The first is

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that the junctions have an inductive reactance. That is,

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similarly to inductors, the voltage difference across a junction is related to the time

Related Topics:
Inductors - Voltage difference

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rate of change of the current. The second is

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that a constant voltage across a junction will produce an oscillating

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current through the barrier, and vice versa. Thus, Josephson junctions

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convert a direct-current voltage to an alternating-current current.

Related Topics:
Direct-current - Alternating-current

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There are two general types of Josephson junctions: overdamped and

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underdamped. In overdamped junctions, the barrier is conducting (normal metal or superconductor bridge).

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The effects of the junction's internal electrical resistance will be

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large compared to its small capacitance. An overdamped junction

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will quickly reach a unique equilibrium state for any given set of

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conditions. The barrier of an underdamped junction is an insulator. The effects of the junction's internal resistance

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will be minimal. Underdamped junctions do not have unique equilibrium

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states, but are hysteretic.

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