A SQUID uses Josephson junctions in a loop made from a superconductor to detect changes in magnetic flux.
A superconducting loop containing one Josephson junction and coupled inductively to a radio-frequency resonator. Its flux-dependent nonlinear inductive response changes the resonator signal. A DC SQUID instead uses two junctions and can turn their critical-current interference into a voltage modulation under bias. Inductance, junction dynamics, noise and feedback determine the practical transfer function.
A SQUID with two Josephson junctions in a superconducting loop. For equal junctions, negligible self-inductance and no intrinsic phase offset, adding their sinusoidal currents gives the displayed flux-dependent critical current. An rf SQUID instead has one junction and uses loop inductance.
For an ideal symmetric two-junction interferometer with negligible self-flux, the stable zero-current phase is zero or pi according to the sign of the flux cosine. Linearization about that stable phase gives positive inductance. The stronger small-current condition is , and fails near a half-integer flux quantum where the ideal critical current vanishes.
The 1964 report established quantum interference in superconducting tunneling. It is an experimental counterpart to the phase-sensitive current predicted for coupled superconductors.[ref]
Quantum Interference Effects in Josephson Tunneling by R. C. Jaklevic and others. Primary experimental report, 1964
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SQUID stands for Superconducting Quantum Interference Device. It is a highly sensitive magnetometer used to measure extremely weak magnetic fields, relying on the principles of superconductivity and quantum interference. Here are some key points about SQUIDs: 1. **Principle of Operation**: SQUIDs operate based on the Josephson effect, where two superconductors are separated by a thin insulator, allowing them to share Cooper pairs of electrons.