Performance of a SQUID read-out system for superconducting tunnel junctions

Superconducting Tunnel Junctions (STJs) have traditionally been read-out using low noise JFET based charge sensitive amplifiers. In some applications, low temperature SQUIDs could be used instead. The advantages are that the first amplification stage is also cooled to cryogenic temperatures and can be physically closer to the STJ, the detector can be voltage biased by means of a small fixed resistor and the detected current pulse shapes can be measured more directly. This work will outline the actual SQUID amplifier configuration and explain its virtues as well as its limitations