Editing Josephson effect (section)

{{short description|Quantum physical phenomenon}}
{{technical|date=September 2018}}
[[File:NISTvoltChip.jpg|thumb|Josephson junction array chip developed by the [[NIST|National Institute of Standards and Technology]] as a standard volt]]

In physics, the '''Josephson effect''' is a phenomenon that occurs when two [[superconductors]] are placed in proximity, with some barrier or restriction between them. The effect is named after the British physicist [[Brian Josephson]], who predicted in 1962 the mathematical relationships for the current and voltage across the weak link.<ref name="possibleNewEffects">{{cite journal |author=Josephson |first=B. D. |year=1962 |title=Possible new effects in superconductive tunnelling |journal=Physics Letters |volume=1 |issue=7 |pages=251–253 |bibcode=1962PhL.....1..251J |doi=10.1016/0031-9163(62)91369-0}}</ref><ref name="Joe">{{cite journal |author=Josephson |first=B. D. |year=1974 |title=The discovery of tunnelling supercurrents |journal= Reviews of Modern Physics|volume=46 |issue=2 |pages=251–254 |bibcode=1974RvMP...46..251J |doi=10.1103/RevModPhys.46.251 |s2cid=54748764|url=https://www.europhysicsnews.org/10.1051/epn/19740503001/pdf }}
:Also in {{cite journal |doi=10.1051/epn/19740503001 |title=The Discovery of Tunnelling Supercurrents |date=1974 |last1=Josephson |first1=B. D. |journal=Europhysics News |volume=5 |issue=3 |pages=1–5 |bibcode=1974ENews...5c...1J }}
</ref> It is an example of a [[macroscopic quantum phenomenon]], where the effects of quantum mechanics are observable at ordinary, rather than atomic, scale. The Josephson effect has many practical applications because it exhibits a precise relationship between different physical measures, such as voltage and frequency, facilitating highly accurate measurements.

The Josephson effect produces a current, known as a [[supercurrent]], that flows continuously without any voltage applied, across a device known as a '''Josephson junction''' (JJ).{{Clarification needed|reason=Does this mean that if the circuit is closed, it pushes the current in a circle? Obviously it can't push current forward forever into a piece of metal that doesn't connect to the beginning again, because a voltage would build up resisting the current.|date=December 2024}} These consist of two or more superconductors coupled by a weak link. The weak link can be a thin insulating barrier (known as a [[superconducting tunnel junction|superconductor–insulator–superconductor junction]], or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivity at the point of contact (S-c-S).

Josephson junctions have important applications in [[Quantum circuit|quantum-mechanical circuits]], such as [[SQUID]]s, [[Superconducting quantum computing|superconducting qubits]], and [[RSFQ]] digital electronics. The [[NIST]] standard for one [[volt]] is achieved by [[Josephson voltage standard|an array of 20,208 Josephson junctions in series]].<ref>Steven Strogatz, ''Sync: The Emerging Science of Spontaneous Order'', Hyperion, 2003.</ref>