Budker is a pioneer of optically pumped atomic magnetometry, having developed SERF and other high-sensitivity vapor-cell magnetometers used across fundamental-symmetry tests, the GNOME global magnetometer network searching for exotic physics, and the CASPEr NMR-based search for axion dark matter. This body of work sits alongside, and directly informs, the field of NV-diamond ensemble sensing (DEER, NMR, T1 relaxometry) that has reached pT/sqrt(Hz)-class sensitivities, since Budker's atomic-vapor techniques set many of the benchmark protocols that solid-state spin sensors now aim to match or exceed.

O'Hare is a dark-matter phenomenologist whose work sits unusually close to instrumentation: he is the principal theorist of the 'neutrino fog' that limits direct-detection experiments, of directional dark matter detection (using the daily modulation of the WIMP wind to distinguish signal from background), and of the axion and ultralight dark-matter searches that increasingly rely on quantum sensors — haloscopes, comagnetometers, NMR-based searches and atomic magnetometers. He writes the sensitivity projections that tell experimentalists which quantum sensor to build. Positioned against the established body of NV-ensemble quantum sensing work — DEER, nanoscale NMR and T1 relaxometry protocols operating at pT/sqrt(Hz) field sensitivity — the axion/ALP search programme he works on consumes spin-ensemble magnetometry directly: CASPEr-class experiments are, in effect, precision NMR magnetometers operating far below pT/sqrt(Hz), and his phenomenology sets the sensitivity targets they aim at. Theory PI with strong experimental engagement.