A microwave SQUID multiplexer optimized for bolometric applications

A microwave superconducting quantum interference device multiplexer has been optimized for reading out large arrays of superconducting transition-edge sensor (TES) bolometers. We present the scalable cryogenic multiplexer chip design that may be used to construct an 1820-channel multiplexer for the 4-8GHz rf band. The key metrics of yield, sensitivity, and crosstalk are determined through measurements of 455 readout channels, which span 4-5GHz. The median white-noise level is 45pA/root Hz, evaluated at 2Hz, with a 1/f knee <= 20 mHz after common-mode subtraction. The white-noise level decreases the sensitivity of a TES bolometer optimized for detection of the cosmic microwave background at 150GHz by only 3%. The measured crosstalk between any channel pair is <= 0.3%.