Frequency-domain readout multiplexing of transition-edge sensor arrays

We have demonstrated frequency-domain readout multiplexing of eight channels for superconducting transition-edge sensor bolometer arrays. The multiplexed readout noise is 6.5 pA/√Hz, well below the bolometer dark noise of 15–20 pA/√Hz. We measure an upper limit on crosstalk of 0.004 between channels adjacent in frequency which meets our design requirement of 0.01. We have observed vibration insensitivity in our frequency-domain multiplexed transition-edge sensors, making this system very attractive for telescope and satellite observations. We also discuss extensions to our multiplexed readout. In particular, we are developing a SQUID flux-locked loop that is entirely cold and collaborating on digital multiplexer technology in order to scale up the number of multiplexed channels.