What set the initial conditions of the Universe? I am interested in understanding the origin of the primordial fluctuations, which evolved after the Big Bang into the complicated structure we see today. The prevailing explanation for the remarkable properties of these fluctuations---especially their extreme uniformity---is that the entire observable Universe began with an inflation of a microscopic volume at the earliest times, during which quantum fluctuations became macroscopic. Cosmological observations have confirmed many of inflation's predictions, but there remain undetected observational signatures that would be unique probes of this process.
The violent inflationary phase would produce a background of gravitational waves and imprint a distinctive "B-mode" pattern in the polarization of the cosmic microwave background (CMB), the first light detectable in the Universe. The simplest inflationary models predict a B-mode level that is detectable by next-generation experiments. Since 2011 I have worked with the BICEP/Keck Array CMB experiments, located at the Amundsen-Scott South Pole station, to produce the world's deepest CMB polarization maps and leading constraints on primordial gravitational waves. I have focused on instrument calibration, and led a recent analysis of instrumental systematics that constrained potential contamination of our polarization maps to a level significantly lower than our statistical sensitivity. These calibration techniques will become even more important in future experiments such as BICEP Array and CMB-S4, for which I am leading an effort to connect the effect of sidelobe pickup to the project's science goals.