A SQUID multiplexer with superconducting-to-normalconducting switches

Abstract

We present a novel multiplexer scheme for time-division multiplexing in superconducting quantum interference device (SQUID) readout configurations. The channels of our SQUID multiplexer (SQMUX) are dc SQUID sensors which are connected in series to form a column. A superconducting-to-normalconducting switch (SN-switch) in parallel with each channel is actuated in order to activate or deactivate an individual channel of the column. With a switch in the normalconducting state, its corresponding SQUID channel is active and sensitive to an input signal. When a switch is in the superconducting state its corresponding SQUID channel is short-circuited. It is then insensitive to input signals and does not generate noise. The addressing sequence is chosen such that only one SQUID channel is active at a time. We suggest employing SN-switches which are based on dc SQUIDs themselves. Doing so enables the addressing signals of the SN-switches to be applied inductively, i.e., galvanically isolated. The SQMUX operation is demonstrated in a configuration where both the SN-switches and the sensing SQUIDs are based on SQUID series arrays.