Key performance characteristics are demonstrated for the microwave SQUID multiplexer (μMUX) coupled to transition edge sensor (TES) bolometers that have been optimized for cosmic microwave background (CMB) observations. In a 64-channel demonstration, we show that the μMUX produces a white, input referred current noise level of 29~pA/Hz at -77~dB microwave probe tone power, which is well below expected fundamental detector and photon noise sources for a ground-based CMB-optimized bolometer. Operated with negligible photon loading, we measure 98~pA/Hz in the TES-coupled channels biased at 65% of the sensor normal resistance. This noise level is consistent with that predicted from bolometer thermal fluctuation (i.e., phonon) noise. Furthermore, the power spectral density exhibits a white spectrum at low frequencies (∼~100~mHz), which enables CMB mapping on large angular scales that constrain the physics of inflation. Additionally, we report cross-talk measurements that indicate a level below 0.3%, which is less than the level of cross-talk from multiplexed readout systems in deployed CMB imagers. These measurements demonstrate the μMUX as a viable readout technique for future CMB imaging instruments.
@article{arxiv.1710.04326,
title = {Microwave SQUID Multiplexer demonstration for Cosmic Microwave Background Imagers},
author = {B. Dober and D. T. Becker and D. A. Bennett and S. A. Bryan and S. M. Duff and J. D. Gard and J. P. Hays-Wehle and G. C. Hilton and J. Hubmayr and J. A. B. Mates and C. D. Reintsema and L. R. Vale and J. N. Ullom},
journal= {arXiv preprint arXiv:1710.04326},
year = {2017}
}