  For precision coherent measurements with ensembles of quantum spins the
relevant Figure-of-Merit (FOM) is the product of polarized spin density and
coherence lifetime, which is generally limited by the dynamics of the spin
environment. Here, we apply a coherent spectroscopic technique to characterize
the dynamics of the composite solid-state spin environment of Nitrogen-Vacancy
(NV) centers in room temperature diamond. For samples of very different NV
densities and impurity spin concentrations, we show that NV FOM values can be
almost an order of magnitude larger than previously achieved in other
room-temperature solid-state spin systems, and within an order of magnitude of
the state-of-the-art atomic system. We also identify a new mechanism for
suppression of electronic spin bath dynamics in the presence of a nuclear spin
bath of sufficient concentration. This suppression could inform efforts to
further increase the FOM for solid-state spin ensemble metrology and collective
quantum information processing.
