» For other uses, see Squid (disambiguation). Superconducting Quantum Interference Devices (SQUID) are very sensitive magnetometers used to measure extremely small magnetic fields, based on superconducting loops containing Josephson junctions. They are sensitive enough to measure fields as low as 5 aT within a few days of averaged measurements. Their noise levels are as low as 3 fT·Hz-½. For comparison, a typical refrigerator magnet produces 0.01 tesla (10-2 T), and some processes… (More on Squid)