What Is the Josephson Effect?

Andrew Kirmayer
Andrew Kirmayer
Scientist with beakers
Scientist with beakers

The Josephson Effect is the passage of paired electrons through a thin, insulating dielectric barrier placed between two superconductors. A cooper pair of electrons passes through the insulating layer via a tunneling effect. There is no voltage drop while the current stays below a specific level, which is known as the critical current. Under constant, positive voltages, alternating currents as well as direct currents from the passage of electrons are maintained. The effect was predicted by theory in the early 1960s by Brian D. Josephson, and is used to take measurements of very low temperatures and in Josephson junction circuits that can rapidly switch signals to store data.

Electrons pass through an insulating film that is microscopically thin. The Josephson Effect can be controlled by applying a magnetic field which reduces the strength of a supercurrent across the barrier. Magnetic fields are blocked from entering the interior of the Josephson junction by fractional vortices. Current strength rises and falls at different points while the field strength is intensified, allowing for signal passage and switching to be controlled.

When the superconductors are exposed to direct current, electron pairs are passed through a barrier as electromagnetic waves are released, which results in the production of small quantities of light instead of heat. The Josephson Effect can also be applied to radio electronics used in extremely cold conditions, because a Josephson junction can work like an electromagnetic oscillation sensor. Circuits based on this junction can also store data, and can be manufactured into tight spaces because they are so efficient, so use in computers is possible.

The Josephson Effect occurs at very low temperatures, and is most efficient at temperatures close to zero degrees Kelvin (about -460&deg:F). Systems that use this effect can be loosely connected to measure magnetic fields. They can also generate low levels of power as part of generators that can be designed to be switched over many frequencies. How the Josephson Effect is used depends on an engineer’s knowledge of quantum physics, and it is measured by using a variety of complex mathematical formulas.

Instruments that incorporate Josephson junctions use the Josephson Effect to make precise dimensional measurements, amplify electromagnetic signals, and drive fast computers. A Josephson tunnel junction switches signals faster than any other semiconductor switch. Such a system can operate at direct current or microwave frequencies, so superconductors can be used in many different metrology and computing applications.

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      Scientist with beakers