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Rotating frame spin dynamics of a Nitrogen-Vacancy center in a diamond nanocrystal

We investigate the spin dynamics of a Nitrogen-Vacancy (NV) center contained in an individual diamond nanocrystal in the presence of continuous microwave excitation. Upon periodic reversal of the microwave phase, we observe a train of 'Solomon echoes' that effectively extends the system coherence lifetime to reach several tens of microseconds, depending on the microwave power and phase inversion rate. Starting from a model where the NV center interacts with a bath of paramagnetic defects on the nanocrystal surface, we use average Hamiltonian theory to compute the signal envelope from its amplitude at the echo maxima. Comparison between the effective Rabi and Solomon propagators shows that the observed response can be understood as a form of higher-order decoupling from the spin bath.