Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control

Abstract

Quantum spin dephasing is caused by inhomogeneous coupling to the environment, with resulting limits to the measurement time and precision of spin-based sensors. The effects of spin dephasing can be especially pernicious for dense ensembles of electronic spins in the solid state, such as nitrogen-vacancy (NV) color centers in diamond. We report the use of two complementary techniques, spin-bath driving, and double quantum coherence magnetometry, to enhance the inhomogeneous spin dephasing time (T_{2}^{*}) for NV ensembles by more than an order of magnitude. In combination, these quantum control techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing mechanisms, including crystal strain gradients and dipolar interactions with paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio by a factor of two. Applied independently, spin-bath driving and double quantum coherence magnetometry elucidate the sources of spin ensemble dephasing over a wide range of NV and bath spin concentrations. These results demonstrate the longest reported T_{2}^{*} in a solid-state electronic spin ensemble at room temperature and outline a path towards NV-diamond dc magnetometers with broadband femtotesla sensitivity.