Noise measurements in a composite niobium/YBCO SQUID and determination of the magnetic noise by direct measurement

The noise performance of a composite niobium/YBCO point contact two-hole SQUID was measured at 4.2 K in both RF and DC bias modes. The noise was measured by a technique which allowed the flux noise component to be measured. The flux noise was found to be the same in both bias modes. A direct measurement of the noise in a single hole in the same sample was made as a function of temperature and was found to display two peaks. Possible causes are discussed.