SQUID noise as a function of temperature: a survey of three SQUID´s

The temperature dependence of SQUID noise was tested over a temperature range from 0.3-4 K for SQUID´s of three different manufactures, two designed for user supplied pick-up coils and one a magnetometer. A SQUID-based picovoltmeter, designed to reduce noise contributions for cables and electronics was used to read out the signal from the SQUID being investigated. The data were taken in support of a physics experiment which will use SQUID´s to measure the precession frequency of spin polarized ³He, acting as a comagnetometer with spin polarized ultra cold neutrons (UCN). The final aim of the experiment is to measure the neutron electric dipole moment to 4×10^-28 ecm. The ³He and UCN will be in a bath at temperatures <0.5 K. The noise performance of the SQUID´s at these temperatures must be well understood before the experiment. The results of the noise studies as a function of temperature are presented for the three SQUID´s and their behavior is compared to theoretical predictions based on SQUID parameters.