Use of low-noise dc-SQUIDs in fundamental physics experiments

The noise performance of dc-SQUIDs (Superconducting Quantum Interference Devices), which nowadays can reach values close to the quantum limit, makes them very attractive as amplifiers for experiments using low temperatures and demanding for extremely high sensitivity. After reviewing the working principle of the dc-SQUID, we describe a thin-film device with a new structure, which allowed us to reach an energy sensitivity of 5.5 h- at 0.9 K and a good coupling with a large input coil. At last we discuss some fundamental physics experiments which take advantage from the SQUID use.