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The pursuit of B-mode polarization in the cosmic microwave background (CMB) can be seen as one part of a three-pronged attack to constrain the post-inflationary axion dark matter scenario. This model allows a high inflationary energy and predicts the axion mass in the cm-wave frequency range. This intriguing model is being probed by (1) direct measurements of inflationary energy scale using CMB B-modes, (2) tightening constraints on isocurvature fluctuations from CMB E-modes, and (3) direct searches of QCD axion dark matter in the frequency range between 5 and 50 GHz.
After the intro I will describe three experimental programs, each targeting one of these three probes: (a) the BICEP/SPT program, a South Pole-based CMB observatory that currently leads the measurements in B-modes; (b) the AliCPT program based on the northern hemisphere, which will expand the sky coverage of ground-based CMB and improve constraints on isocurvature modes; (c) ADMX-VERA (Volume Enhanced Resonant Axion) Experiment, which uses novel geometries in the design of axion dark matter detectors to avoid the steep sensitivity degradation toward high frequencies.