BICEP2. II. Experiment and three year data set
We report on the design and performance of the BICEP2 instrument and on its three year data set. BICEP2 was designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 1deg 5deg(l 40 200) near the expected peak of the B mode polarization signature of primordial gravitational waves from cosmic inflation. Measuring B modes requires dramatic improvements in sensitivity combined with exquisite control of systematics. The BICEP2 telescope observed from the South Pole with a 26 cm aperture and cold, on axis, refractive optics. BICEP2 also adopted a new detector design in which beam defining slot antenna arrays couple to transition edge sensor (TES) bolometers, all fabricated on a common substrate. The antenna coupled TES detectors supported scalable fabrication and multiplexed readout that allowed BICEP2 to achieve a high detector count of 500 bolometers at 150 GHz, giving unprecedented sensitivity to B modes at degree angular scales. After optimization of detector and readout parameters, BICEP2 achieved an instrument noise equivalent temperature of $15.8\ \mu \mathrm{K}\sqrt{\mathrm{s} The full data set reached Stokes Q and U map depths of 87.2 nK in square degree pixels (5farcm2 mK) over an effective area of 384 deg2 within a 1000 deg2 field. These are the deepest CMB polarization maps at degree angular scales to date. The power spectrum analysis presented in a companion paper has resulted in a significant detection of B mode polarization at degree scales.