Tucker Elliott (UCSD) "Characterization of Multiplexed Transition Edge Sensor Bolometers for the POLARBEAR-2 Cosmic Microwave Background Experiment"

ABSTRACT:
Measurements of the Cosmic Microwave Background (CMB) temperature anisotropies and E-mode polarization have proven to be essential to our understanding of early universe cosmology by providing independent and strong evidence in favor of the Lambda-CDM cosmological model. However, there is still untapped information in the CMB. Current-generation CMB experiments aim to measure the very faint B-mode polarization signal in order to find evidence of cosmic inflation and to measure the sum of the neutrino masses.
POLARBEAR-2 (PB-2) is a CMB polarization experiment located in northern Chile’s Atacama Desert at an altitude of 5,200 meters. PB-2 is currently operating with over 7,500 superconducting Transition Edge Sensor (TES) bolometers with a scheduled increase to over 22,000 TES bolometers in the next year. PB-2 uses Digital Frequency Division Multiplexed (DfMux) readout to combine the bias and readout lines for sets of forty detectors onto a single pair of conductors in order to reduce cost and cryogenic complexity.
Superconducting (TES) bolometers are the gold-standard technology for observing the CMB because they can be used to make photon noise limited measurements. This is why CMB experiments continue to increase their detector counts – to achieve higher sensitivity. However in order to achieve optimal sensitivity, the TES and multiplexing system must meet certain specifications. In this talk, I will describe the requirements imposed on the detectors and readout system and the measurements I have performed at the University of California San Diego to characterize the detectors and readout system of the first and second PB-2 cryogenic receivers.