NV electronic spin coherence time approaching one second

We demonstrate an improvement of more than two orders of magnitude in the spin coherence time (T2) of NV centers compared to previous measurements: T2 $\sim$ 0.5 s at 77K. By employing dynamical decoupling pulse sequences to suppress NV spin decoherence due to magnetic noise, we found that T2 is limited to approximately half of the longitudinal spin relaxation time (T1) over a wide range of temperatures, which we attribute to phonon-induced decoherence. Our results apply to ensembles of NV spins and do not depend on the optimal choice of a specific NV, which could advance quantum sensing, enable squeezing and many-body entanglement in solid-state spin ensembles, and open a path to simulating a wide range of driven, interaction-dominated quantum many-body Hamiltonians.