  Spin complexes comprising the nitrogen-vacancy (NV) center and neighboring
spins are being considered as a building block for a new generation of
spintronic and quantum information processing devices. Because assembling
identical spin clusters is difficult, new strategies are in order to determine
individual node structures with the highest precision. Here we use a pulse
protocol to monitor the time evolution of the 13C ensemble in the vicinity of a
NV center. We observe long-lived time correlations in the nuclear spin
dynamics, limited by NV spin-lattice relaxation. We use the host 14N spin as a
quantum register, and demonstrate that hyperfine-shifted resonances can be
separated upon proper NV initialization. Intriguingly, we find that the
amplitude of the correlation signal exhibits a sharp dependence on the applied
magnetic field. We discuss this observation in the context of the
quantum-to-classical transition proposed recently to explain the field
dependence of the spin cluster dynamics.
