Low frequency noise in flux-locked DC squids

We present the results of measurements of the noise of open loop and flux-locked DC SQUIDs at frequencies from 100 kHz to 10-4 Hz. The SQUIDs studied in this work were low l/f noise devices fabricated at IBMs East Fishkill facility. Measurements were made in DC magnetic fields of 2x103 G using conventional shielding and also in an ultra-low magnetic field environment of 10-7 G using expanded superconducting foil shields and a feedback-controlled slow cooling technique. The open-loop results are consistent with the earier work of Teschel. We include a description of the apparatus used for obtaining the various noise measurements. © 1989 IEEE