Coherent excitation dynamics of single spins in diamond

The spin dynamics of nitrogen vacancy (NV) centers in diamond during non-resonant optical excitation are fundamentally important for both optical initialization and fluorescence-based spin read-out. While such processes rely on the preservation of the longitudinal spin projection, an NV center's lack of orbital coherence at room temperature might suggest that its quantum phase would be destroyed during excitation. We address this question using Ramsey experiments, quantum process tomography and theoretical modeling and establish limits on the coherence loss of an NV center during optical excitation [1]. By treating the excitation and spin precession as a quantum process, we measure a process fidelity of $F=0.87\pm0.03$, which includes excited state dephasing during measurement. Extrapolation to the moment of optical excitation yields $F\approx0.95$. These results provide a new understanding of NV centers' spin coherence during optical excitation and are crucial for efforts to use coherent evolution in the excited state for spin control. \\[4pt] [1] G. D. Fuchs, A. L. Falk, V. V. Dobrovitski, and D. D. Awschalom, \emph{submitted} (2011)