| Summary: | We study, both theoretically and experimentally, the free induction decay (FID) of the electron spin associated with a single nitrogen–vacancy defect in high-purity diamond, where the main source of decoherence is the hyperfine interaction with a bath of ^13 C nuclear spins. In particular, we report a systematic study of the FID signal as a function of the strength of a magnetic field oriented along the symmetry axis of the defect. On average, an increment of the coherence time by a factor of $\sqrt {5/2}$ is observed at high magnetic field in diamond samples with a natural abundance of ^13 C nuclear spins, in agreement with numerical simulations and theoretical studies. Further theoretical analysis shows that this enhancement is independent of the concentration of nuclear-spin impurities. By dividing the nuclear-spin bath into shells and cones, we theoretically identify the nuclear spins responsible for the observed dynamics.
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