A superconducting quantum interference device (SQUID) is a highly sensitive magnetometer used to measure extremely small magnetic fields. It operates based on the principles of quantum mechanics and superconductivity, utilizing a loop of superconducting material with one or two weak links, known as Josephson junctions. These junctions allow for the observation of quantum interference effects, which are crucial for detecting minute changes in magnetic flux. SQUIDs are widely used in various fields, including medical imaging through magnetoencephalography (MEG), geophysics for mineral exploration, and fundamental physics research. Their ability to detect magnetic fields at the femtotesla level makes them invaluable tools in both scientific and industrial applications.