New readout scheme for superconducting tunnel junction arrays

We report on the design and testing of a new readout scheme for Superconducting Tunnel Junction (STJ) arrays. This method drastically reduces the number of connections and electronic circuits required for reading out an array of pixelated detectors. In the specific case of STJs, it eases the manufacturing process and connectivity problems. It is a generic scheme in that it could also be applied to different kinds of detector arrays. The experiments reported are simply a proof of principle and were carried out on a two-by-two array of STJs using optical photon excitation on tantalum-based detectors. If one uses charge sensitive amplifiers with junction field-effect transistors (JFETs) we verify that the resolution degrades mainly due to capacitance increase at the input node. However, since each detector is read-out by two independent circuits, these two outputs can be combined to increase the signal-to-noise level. We show that the equivalent noise charge at the input worsens by about a factor <N as compared to individual read-out and for a N×N array, consistent with our theoretical predictions. If one uses Superconducting Quantum Interference Devices (SQUIDs) as pre-amplifying stage, there should be no considerable increase in electronic noise related to this new readout scheme.