  Spin relaxometry with nitrogen-vacancy (NV) centers in diamond offers a
spectrally selective, atomically localized, and calibrated measurement of
microwave-frequency magnetic noise, presenting a versatile probe for condensed
matter and biological systems. Typically, relaxation rates are estimated with
curve-fitting techniques that do not provide optimal sensitivity, often leading
to long acquisition times that are particularly detrimental in systems prone to
drift or other dynamics of interest. Here we show that adaptive Bayesian
estimation is well suited to this problem, producing dynamic relaxometry pulse
sequences that rapidly find an optimal operating regime. In many situations
(including the system we employ), this approach can speed the acquisition by an
order of magnitude. We also present a four-signal measurement protocol that is
robust to drifts in spin readout contrast, polarization, and microwave pulse
fidelity while still achieving near-optimal sensitivity. The combined technique
offers a practical, hardware-agnostic approach for a wide range of NV
relaxometry applications.
