Centro S3, CNR-Istituto di Nanoscienze, I-41125 Modena, Italy.
Quantum Technology Lab, Dipartimento di Fisica dell'Università degli Studi di Milano, I-20133 Milano, Italy.
Phys Rev Lett. 2018 Jun 29;120(26):260503. doi: 10.1103/PhysRevLett.120.260503.
We address metrological protocols for the estimation of the intensity and the orientation of a magnetic field, and show that quantum-enhanced precision may be achieved by probing the field with an arbitrary spin at thermal equilibrium. A general expression is derived for the ultimate achievable precision, as given by the quantum Fisher information. The optimal observable is shown to correspond to the spin projection along a temperature-dependent direction, and allows a maximally precise parameter estimation also through ensemble measurements. Finally, we prove the robustness of our scheme against deviations of the measured spin projection from optimality.
我们介绍了用于估计磁场强度和方向的计量学协议，并表明通过用处于热平衡状态的任意自旋探测磁场，可以实现量子增强的精度。推导出了由量子 Fisher 信息给出的最终可达到的精度的一般表达式。最优可观测量对应于沿温度相关方向的自旋投影，并且还允许通过整体测量进行最大精度的参数估计。最后，我们证明了我们的方案对测量的自旋投影偏离最优状态的稳健性。
