Decoupling magnetic dipolar interactions between electron spins in diamond

Synthetic diamond produced by high-pressure, high-temperature (HPHT) techniques is known to contain inhomogeneous distributions of substitutional nitrogen (P1) defects. Electron irradiation of these samples creates nitrogen-vacancy (NV) centers with a range of local P1 concentrations which determine their coherence times. Extending the coherence times of ensembles of P1 or NV spins requires decoupling both local Zeeman disorder and the magnetic dipolar interactions between spins. While the CPMG pulse sequence can simultaneously decouple disorder and dipolar interactions between dissimilar spins, it does not decouple interactions between spins of the same species. Decoupling such interactions is becoming important as systems of interacting P1 and NV centers are increasingly used for many-body physics and ensemble quantum sensing. Here we explore the performance of a series of dipolar decoupling sequences such as epsilon-CPMG and WAHUHA on both weakly and strongly interacting spins using inductively detected bulk electron spin resonance experiments. We find that for the weakly dipolar coupled NV centers, epsilon-CPMG shows enhancement of coherence for slight over and under rotations, while WAHUHA has little effect. For the strongly dipolar coupled P1 centers, epsilon-CPMG shows a small enhancement of coherence, while WAHUHA shows a dramatic increase in coherence.