AI 中文总结
研究在实际与标称自旋频率有未知失谐时的直流磁场单比特拉姆齐磁力测量，分析失谐对估计的偏差影响，构建复合脉冲制备和读出方法抵消失谐到一阶，评估其性能并证明能抑制失谐诱导偏差。
AI 中文摘要
量子传感估计探针状态中编码的物理参数；对于独立自旋探针，精度遵循标准量子极限。传感精度研究通常假设模型中的参数（如噪声）是已知的。但实际中这些参数并不总是已知，假设值与实际值的不匹配会引发系统误差。本文研究了在实际与标称自旋频率之间存在未知失谐情况下的直流磁场单比特拉姆齐磁力测量：第一个脉冲使量子比特进入其两个状态的叠加，待感测磁场在曝光阶段添加相对相位，第二个脉冲实现读出。在该设置中，磁场仅在曝光阶段起作用，而失谐在整个协议过程中起作用。分析了失谐如何使估计产生偏差，阻碍总估计误差遵循标准量子极限。接着构建了一种复合脉冲制备和读出方法，利用磁场和失谐作用区间的差异将失谐抵消到一阶。评估了该复合脉冲协议的性能，表明其抑制了失谐诱导偏差。
英文摘要
Quantum sensing estimates a physical parameter encoded in the state of a probe; with independent spin probes the precision follows the standard quantum limit. Studies of sensing precision often assume that the parameters entering the model, such as the noise, are known. In practice these parameters are not always known, and a mismatch between the assumed and actual values induces a systematic error. Here we study single-qubit Ramsey magnetometry of a DC magnetic field under an unknown detuning between the actual and nominal spin frequencies: A first pulse puts the qubit into a superposition of its two states, the field to be sensed then adds a relative phase during an exposure stage, and a second pulse enables the readout. In our setting, the field acts only during the exposure stage, whereas the detuning acts throughout the whole protocol. We analyze how the detuning biases the estimate, preventing the total estimation error from following the standard quantum limit. We then construct a composite-pulse preparation and readout that exploits the difference in the intervals over which the field and the detuning act to cancel the detuning to first order. We evaluate the performance of this composite-pulse protocol and show that it suppresses the detuning-induced bias.
Comments9 pages, 3 figures
