Progress in understanding of high-transition-temperature SQUIDs

In this overview, we compare experimental results with predictions of analytical theories of rf SQUIDs and dc SQUIDs, valid up to the limit of high thermal fluctuations, and also with extensive dc SQUIDs simulations. Data derived from measurements of amplitude-frequency characteristics of rf SQUIDs, plus direct characterization of junctions after opening the SQUID loop, gave a satisfactory quantitative agreement with theory. For dc SQUIDs, white noise was typically higher and the transfer function lower than predicted by analytical theory and by simulations. The origin of these discrepancies remains unknown.