Saturating the quantum Cram\'er-Rao bound and measuring the related quantum Fisher information in a nitrogen-vacancy center in diamond.
Yu Liu, Min Yu, Pengcheng Yang, Musang Gong, Qingyun Cao, Shao‐Liang Zhang, Haibin Liu, Markus Heyl, Tomoki Ozawa, Nathan Goldman, Jianming Cai · arXiv (Cornell University) · 2020
The quantum Cramer-Rao bound sets a fundamental limit on the accuracy of unbiased parameter estimation in quantum systems, relating the uncertainty in determining a parameter to the inverse of the quantum Fisher information. We experimentally demonstrate near saturation of the quantum Cramer-Rao bound in the phase estimation of a solid-state spin system, provided by a nitrogen-vacancy center in diamond. This is achieved by comparing the experimental uncertainty in phase estimation with an independent measurement of the related quantum Fisher information. The latter is finely extracted from coherent dynamical responses of the system under weak parametric modulations, without performing any quantum-state tomography. Our method offers a versatile and powerful tool to explore the fundamental role of the quantum Fisher information in quantum technologies.