Recent Developments of Commercially Fabricated Horn Antenna-Coupled Transition-Edge Sensor Bolometer Detectors for Next-Generation Cosmic Microwave Background Polarimetry Experiments
Aritoki Suzuki, Elijah Kane, Adrian Tae-Jin Lee, Tiffany Liu, Christopher Raum, Mario Renzullo, Patrick Truitt, John A. Vivalda, Benjamin Westbrook, Daniel T. Yohannes
For the next generation of Cosmic Microwave Background (CMB) experiments, kilopixel arrays of Transition Edge Sensor (TES) bolometers are necessary to achieve the required sensitivity and their science goals. We are developing read-out electronics for POLARBEAR-2 CMB experiment, which multiplexes 32-TES bolometers through a single superconducting quantum interface device (SQUID). To increase both the bandwidth of the SQUID electronics and the multiplexing factor, we are modifying cold wiring and developing LC filters, and a low-inductance superconducting cable. Using these components, we will show frequency domain multiplexing up to 3 MHz.
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.