Fig. 1. Experimental scheme and main result. (a) Experimental setup and a single N-V center in diamond. (b) Electron-spin energy-level of N-V center and the spin dynamics of the pumping process at room temperature. The transition of pumping laser (532 nm) is indicated by the green solid line, while the radiative (nonradiative) transition is the red solid (gray dashed) line. (c) Pulse sequence of the electron-spin Rabi oscillation using repeatedly pulse-width-modulated laser. (d) Effect of pulse-width modulation in electron-spin Rabi oscillation. Blue (red) points are experimental data with 300 ns (4 ns) laser pulses with the pulse sequence shown in (c). The number 33.3% (37.1%) noted in the plot is the contrast value between the ms=0 and ms=−1 spin states using the corresponding scheme. Each data point is obtained from 1010 Rabi sequence repetitions for signal accumulation.

Fig. 2. Numerical simulations and their corresponding experimental results. (a) For laser pulses with three different widths, the highest polarization that can be achieved in simulation is dependent on the repeating times N. (b) The measured contrast using different pulse widths and repetitions in Rabi experiment. (c) There is a continuous decrease of the highest polarization when the pulse width ts is increasing from 4 to 200 ns in simulation. (d) Measured polarization (contrast) for pulse widths from 4 to 50 ns. Each experimental point is obtained from 1010 Rabi sequence [Fig. 1(c)] repetitions for signal accumulation.

Fig. 3. Measured Rabi oscillation in terms of spin contrast for (a) different wait time tw and (b) different laser powers. Each data point is obtained from 1010 Rabi sequence [Fig. 1(c)] repetitions for signal accumulation.

Fig. 4. Mechanism and simulation results. (a) The population transfer P21 and P12 eventually converge to the same value as the repetition N increases. Here, Pij denotes the population transfer from |i⟩ to |j⟩. (b) Difference between P21 and P12, which indicates the net transfer between |1⟩ and |2⟩. (c) Probability (blue) at meta-stable spin-singlet states (|5⟩ and |6⟩) and the corresponding final polarization (red) with the occupation of the laser over all the process ts/(ts+tw). (d) Direct relation between the final polarization and the probability at meta-stable spin-singlet states.