An insight into voltage-biased superconducting quantum interference devices

Abstract

We experimentally studied two important parameters of helium-cooled superconducting quantum interference devices (SQUIDs) in the voltage bias mode: the dynamic resistance Rd and the flux-to-current transfer coefficient ?i/?phi, with different junction shunt resistors RJ. We investigated a voltage-biased SQUID using the direct readout current-to-voltage converter scheme involving an operational amplifier. At higher RJ, the flux-to-voltage conversion coefficient ?V/?phi becomes sufficiently large to effectively suppress the room-temperature amplifier´s noise without any need for additional feedback circuits. The McCumber parameter limits the rise of ?V/?phi. We discuss the performance of voltage-biased SQUIDs at different effective McCumber parameters.