Next-generation CMB cosmology with high-density superconducting sensor readouts

Significantly tighter cosmological constraints on inflation, thermal relics and neutrino mass, as well as searches for departure from Lambda-CDM can be accomplished by advancing towards cosmic-variance-limited measurements of CMB TT, EE, BB power and their cross spectra. I will share a glimpse of the work that my colleagues and I are undertaking towards this goal with new experiments such as BICEP Array, SPT-3G and Simons Observatory. All of these experiments are entering a new era of foreground-, instrument-systematics- and/or gravitational-lensing-dominated searches, requiring new analysis machinery and tricks. Raw sensitivity needs to be scaled another 5-7x to really reach cosmic-variance limits in CMB polarization -- the goal of a next-generation CMB experiment proposed for the late 2020s, called CMB-S4. Since CMB bolometer technology is photon-noise-limited, a sheer 25-50x scaling needs to occur in pixel counts of CMB cameras to enable CMB-S4.  I will discuss RF-SQUID-modulated microwave-multiplexing of transition-edge sensor bolometers as a promising path to achieving high-density readouts for these cameras and will present initial results from proof-of-concept tests of this technology.