A three channel SQUID-system using a multiplexed readout

Conventional multichannel SQUID systems require a number of wires connecting the individual SQUIDs and feedback coils to room-temperature electronics. In order to reduce the heat transport by these wires and avoid the accompanied increased helium losses, the possibility of using a multiplexed readout requiring only a fraction of feed lines than needed by conventional systems was studied. RF SQUIDs were used in the experiments to avoid additional wires for DC bias currents. A bias frequency of 100 MHz was chosen to achieve a sufficiently low flux noise. The influence of modulation frequency and multiplexing frequency on the stability of the flux-locked loop and on the slew rate of the system was studied. Careful optimization of these parameters can lead to a multichannel system which requires only one coaxial cable between room-temperature electronics and all SQUIDs.