Superconducting Quantum Interference Devices

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Superconducting quantum interference devices (SQUIDs) use so-called "flux quantization" as a quantum-based measurement method. These highly sensitive magnetic sensors consist of two superconducting tunnel contacts separated by a thin insulator. The method is based on the quantum mechanical effects of the Josephson effect. The phase difference between the two superconducting contacts is measured, the discrete value of which is proportional to the penetrating magnetic flux.


  • An Exceptionally sensitive method for measuring magnetic flux and low magnetic fields. (in the range of a few nanoteslas (10^-9 tesla) or even less).
  • SQUIDs can be used to create high-resolution magnetic images or to precisely detect the magnetic properties of materials.


  • The measurement requires deep cold (near absolute zero) and is susceptible to external magnetic fields.

Applications: magnetic resonance imaging (MRI), geophysics, protein biophysics, and materials characterization.

The image shows the pairwise tunneling of electron pairs through a barrier in a SQUID. These are based on cryogenics and have been used for years in SQUID magnetometers to measure minimal magnetic fields. (by courtesy of Physikalisch-Technische Bundesanstalt, image has been taken from the article "Quantum magnetic-field sensors".)