View source for The Physics of Superconducting Quantum Interference Devices (SQUIDs)

== Introduction ==
Superconducting Quantum Interference Devices, or [[SQUIDs]], are highly sensitive magnetometers used to measure extremely subtle magnetic fields. They are based on superconducting loops containing Josephson junctions. SQUIDs are among the most sensitive magnetic field detectors available, with noise levels as low as 3 fT Hz−½.

== Principle of Operation ==
The basic principle of operation of a SQUID is the [[Flux Quantization|flux quantization]] in superconducting loops, and the [[Josephson Effect|Josephson effect]]. When a superconducting loop is exposed to a magnetic field, the change in the field induces a current in the loop, according to [[Faraday's Law of Electromagnetic Induction|Faraday's law of electromagnetic induction]]. In a SQUID, the current thus induced produces a magnetic field that opposes the change in the applied field, thus keeping the total magnetic flux through the loop constant.

[[Image:Detail-39929.jpg|thumb|center|A photograph of a SQUID device.|class=only_on_mobile]]
[[Image:Detail-39930.jpg|thumb|center|A photograph of a SQUID device.|class=only_on_desktop]]

== Types of SQUIDs ==
There are two main types of SQUIDs: DC SQUIDs and RF SQUIDs. 

=== DC SQUIDs ===
[[DC SQUID|DC SQUIDs]] have two [[Josephson Junction|Josephson junctions]] in parallel in the superconducting loop. The current-voltage characteristic of a DC SQUID is periodic in the applied magnetic flux, with a period equal to the flux quantum. 

=== RF SQUIDs ===
[[RF SQUID|RF SQUIDs]], on the other hand, have only one Josephson junction in the loop. They operate on the principle of the [[Resonance|resonance]] of the LC circuit formed by the loop and a capacitor.

== Applications ==
SQUIDs have a wide range of applications, from fundamental physics experiments to industrial and medical applications. They are used in [[Magnetic Resonance Imaging|Magnetic Resonance Imaging (MRI)]] for their ability to detect extremely small changes in magnetic fields, in [[Geophysics|geophysics]] for detecting variations in the Earth's magnetic field, and in [[Astrophysics|astrophysics]] for measuring the properties of superconductors.

== See Also ==
* [[Quantum Computing]]
* [[Superconductivity]]
* [[Magnetometer]]

[[Category:Physics]]
[[Category:Superconductivity]]
[[Category:Quantum Mechanics]]
[[Category:random]]