Double dc SQUID for flux-locked-loop operation

Abstract

A novel double dc superconducting quantum interference device (SQUID) is proposed. It consists of two SQUIDs with different geometries in cascade configuration. The structure makes the device particularly suitable for flux-locked-loop operation without need of a room-temperature heterodyne modulation circuitry and a matching network between the SQUID and the preamplifier, thus simplifying the readout electronic system. The noise performance is calculated as a function of the electrical parameters of the device. The noise contribution of the room-temperature preamplifier can be made negligible using appropriate SQUID parameters while the slew rate of the system can approach 106Φ0/s.