What are SQUIDS in physics?

The Superconducting Quantum Interference Device, or SQUID, is an extremely sensitive magnetic flux-to-voltage transducer. The SQUID may be the most sensitive detector of any physical quantity, with an energy resolution that approaches the quantum limit. The extreme sensitivity of the SQUID has caused it to be incorporated into a great variety of systems. SQUIDs have been used to measure cortical activity in the human brain and to search for gravity waves.