Dynamically Polarizing Spin Register of N-V Centers in Diamond Using Chopped Laser Pulses

Nuclear spins nearby nitrogen-vacancy (N-V ) centers in diamond are excellent quantum memory for quantum computing and quantum sensing, but are difficult to initialize due to their weak interactions with the environment. Here, we propose and demonstrate a magnetic-field-independent, deterministic, and highly efficient polarization scheme by introducing chopped laser pulses into the double-resonance initialization method. With this method, we demonstrate the initialization of a single-nuclear-spin system approaching 98.1 % and a ¹⁴N-1³C double-nuclear-spin system approaching 96.8 % at room temperature. The initialization is limited by a nuclear-spin depolarization effect due to chopped laser excitation. Our approach could be extended to N-V systems with more nuclear spins and would be a useful tool in future applications such as nano-magnetic resonance imaging and single-cell NMR.