Microwave SQUID multiplexer demonstration for cosmic microwave background imagers

Abstract

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 is white over a range of frequencies down to ~ 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.

Simons Observatory large aperture telescope receiver design overview

“…Thus the warm SMuRF electronics will be used to read out the LATR arrays using cold microwave SQUID multiplexers (µmux) manufactured by National Institute of Standards and Technology (NIST), which target much higher multiplexing factors (∼2000 detectors per transmission line pair). 16 The readout electronics for the LATR µmux system include four sets of readout harness inserts that will penetrate the vacuum shell (square cutouts in Fig. 3).…”

BoloCalc: a sensitivity calculator for the design of Simons Observatory

“…34,35 Therefore, amplifier-induced readout noise can be modeled as a noise-equivalent current (NEI), referred to the power at the detector by the inverse of the detector responsivity. For a voltage-biased bolometer operating with negative feedback and high loop gain L 1, responsivity is ≈ 1/V bias , 36,37 and readout NEP is given by…”

Prime-Cam: a first-light instrument for the CCAT-prime telescope

“…26,27 These arrays will be based on TES detectors read out using superconducting quantum interference device (SQUID) multiplexers ( Figure 5). 28 In both TES arrays, lithographically defined superconducting microwave components separate the two polarizations and four frequencies onto different microstrip lines. For the broadband detectors, the change in optical power for each polarization and frequency is converted to heat and measured with a superconducting TES bolometer.…”

“…The Prime-Cam TES arrays will be read out using microwave SQUID (µSQUID) readout, in which each TES is inductively coupled through an RF-SQUID to its own microresonator at a unique microwave frequency 35,48 (between 4 and 8 GHz). 28,36 Thousands of TES-coupled resonators are then coupled to a shared feedline and read out simultaneously using standard RF readout techniques. KID arrays can use the same readout electronics as the TES arrays, but for KIDs, the KID itself is the resonator, 30 which greatly simplifies the array design.…”