  We theoretically investigate spin decoherence of a single nitrogen-vacancy
(NV) center in diamond. Using the spin coherent state P-representation method,
coherence evolution of the NV center surrounded by nitrogen electron spins (N)
is simulated. We find that spin decoherence time as well as free-induction
decay of the NV center depend on the spatial configuration of N spins. Both the
spin decoherence rate (1/T2) and dephasing rate (1/T2*) of the NV center
increase linearly with the concentration of the N spins. Using the
P-representation method, we also demonstrate extracting noise spectrum of the N
spin bath, which will provide promising pathways for designing an optimum pulse
sequence to suppress the decoherence in diamond.
