  The nitrogen-vacancy (N-V) center in diamond is a widely-used platform for
quantum information processing and metrology. The electron-spin state of N-V
center could be initialized and readout optically, and manipulated by resonate
microwave fields. In this work, we analyze the dependence of electron-spin
initialization on widths of laser pulses. We build a numerical model to
simulate this process and verify the simulation results in experiment. Both
simulations and experiments reveal a fact that shorter laser pulses are helpful
to the electron-spin polarization. We therefore propose to use extremely-short
laser pulses for electron-spin initialization. In this new scheme, the
spin-state contrast could be improved about 10% in experiment by using laser
pulses as short as 4 ns in width. Furthermore, we provide a mechanism to
explain this effect which is due to the occupation time in the meta-stable
spin-singlet states of N-V center. Our new scheme is applicable in a broad
range of NV-based applications in the future.
