Precise control of the resonant frequency of a spin qubit is of fundamental importance to quantum sensing protocols. We demonstrate a control technique on a single nitrogen-vacancy (NV) centre in diamond where the applied magnetic field is modified by fine-tuning a permanent magnet's magnetisation via temperature control. Through this control mechanism, nanoscale cross-relaxation spectroscopy of both electron and nuclear spins in the vicinity of the NV centre are performed. We then show that through maintaining the magnet at a constant temperature an order of magnitude improvement in the stability of the NV qubit frequency can be achieved. This improved stability is tested in the polarisation of a small ensemble of nearby $^{13}$C spins via resonant cross-relaxation and the lifetime of this polarisation explored. The effectiveness and relative simplicity of this technique may find use in the realisation of portable spectroscopy and/or hyperpolarisation systems.

中文翻译：

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通过热磁场控制进行高精度单量子位调谐

精确控制自旋量子位的谐振频率对于量子传感协议至关重要。我们展示了对金刚石中单个氮空位 (NV) 中心的控制技术，其中通过温度控制微调永磁体的磁化强度来修改施加的磁场。通过这种控制机制，在 NV 中心附近进行了电子和核自旋的纳米级交叉弛豫光谱。然后我们表明，通过将磁铁保持在恒定温度，可以实现 NV 量子位频率稳定性的数量级改进。这种改进的稳定性在附近 $^{13}$C 自旋的小集合的极化中通过共振交叉弛豫进行了测试，并探索了这种极化的寿命。