Nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond exhibit long spin-coherence times, optical initialization, and optical-spin readout under ambient conditions, making them excellent quantum sensors. However, the conventional scheme for charge-state initialization based on off-resonant green excitation results in significant state-preparation errors, typically around $30\mathrm{\%}$. One method for improving charge-state initialization fidelity is to use multicolor excitation, which has been demonstrated to achieve a near-unity preparation fidelity for bulk $\mathrm{N}$-$V$ centers by using a few milliseconds of near-infrared (NIR) (5-mW) and green ($10$-$\text{μ}\mathrm{W}$) excitation. The translation of such schemes to $\mathrm{N}$-$V$ centers near the diamond surface with higher-efficiency optical pumping would enable new applications in nanoscale sensing. Here, we demonstrate a protocol for efficient charge initialization of shallow $\mathrm{N}$-$V$ centers between 5 nm and 15 nm from the diamond surface. By carefully studying the charge dynamics of shallow $\mathrm{N}$-$V$ centers, we identify a region of parameter space that allows for near-unity (95%) charge initialization within $300\text{μ}\mathrm{s}$ of NIR (905-nm, 1-mW) and green (520-nm, $10$-$\text{μ}\mathrm{W}$) excitation. The time to 90% charge initialization can be as fast as $10\text{μ}\mathrm{s}$ for 4 mW of NIR and $39\text{μ}\mathrm{W}$ of green illumination. This fast, efficient charge initialization protocol will especially benefit nanoscale sensing applications in which state-preparation errors currently prohibit scaling, such as measuring higher-order multipoint correlators.

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• Magnetometry
• Quantum information processing
• Quantum sensing
• Quantum state engineering
• Nitrogen vacancy centers in diamond
• Infrared techniques
• Optical microscopy
• Optically detected magnetic resonance