Toward a 10,000-element B-Mode Experiment

In this paper, we introduce two compact, large-throughput CMB polarimeter designs (POLAR1 and BICEP3). These pathfinder experiments will pave the way for a comprehensive multi-frequency South Pole B-mode survey that, when jointly analyzed with arcminute-scale polarization data, can conclusively answer the question whether there is an appreciable fraction (>1%) of the primordial perturbations in the form of tensor modes (gravitational waves).