A Microwave SQUID Multiplexer Optimized for Bolometric Applications

TL;DR

This paper presents an optimized microwave SQUID multiplexer design for large TES bolometer arrays, demonstrating high yield, low noise, minimal crosstalk, and negligible impact on detector sensitivity in cosmic microwave background experiments.

Contribution

The authors develop and validate a scalable 1820-channel cryogenic multiplexer chip for TES bolometers, improving multiplexing performance in the 4-8 GHz band.

Findings

Median white-noise level of 45 pA/√Hz at 2 Hz

Crosstalk between channels ≤ 0.3%

Sensitivity reduction of only 3% for CMB detectors

Abstract

A microwave SQUID multiplexer ($\mu$MUX) has been optimized for coupling to large arrays of superconducting transition-edge sensor (TES) bolometers. We present the scalable cryogenic multiplexer chip design in a 1820-channel multiplexer configuration for the 4-8 GHz rf band. The key metrics of yield, sensitivity, and crosstalk are determined through measurements of 455 readout channels, which span 4-5 GHz. The median white-noise level is 45 pA/$\sqrt{\textrm{Hz}}$, evaluated at 2 Hz, with a 1/f knee $\leq$ 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 150 GHz by only 3%. The measured crosstalk between any channel pair is $\leq$ 0.3%.