Liu Ran, Wu Ze, Yang Xiaodong, Li Yuchen, Zhou Hui, Li Zhaokai, Chen Yuquan, Yuan Haidong, Peng Xinhua
CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China.
Anhui Province Key Laboratory of Scientific Instrument Development and Application, University of Science and Technology of China, Hefei 230026, China.
Natl Sci Rev. 2025 Mar 10;12(5):nwaf091. doi: 10.1093/nsr/nwaf091. eCollection 2025 May.
By leveraging quantum effects, such as superposition and entanglement, quantum metrology promises higher precision than classical strategies. It is, however, a challenging task to achieve the higher precision on practical systems. This is mainly due to difficulties in engineering nonclassical states and performing nontrivial measurements on the system, especially when the number of particles is large. Here we propose a variational scheme with the Loschmidt echo for quantum metrology. By utilizing hardware-efficient ansatzes in the design of variational quantum circuits, the quantum Fisher information (QFI) of the probe state can be extracted from the experimentally measured Loschmidt echo in a scalable manner. This QFI is then used to guide the online optimization of the preparation of the probe state. We experimentally implement the scheme on an ensemble of 10-spin quantum processors and achieve a 12.4-dB enhancement of the measurement precision over the uncorrelated states, which is close to the theoretical limit. The scheme can also be employed on various other noisy intermediate-scale quantum devices, which provides a promising protocol to demonstrate quantum advantages.
通过利用诸如叠加和纠缠等量子效应，量子计量学有望实现比经典策略更高的精度。然而，在实际系统上实现更高的精度是一项具有挑战性的任务。这主要是由于在工程非经典态以及对系统进行非平凡测量方面存在困难，特别是当粒子数量很大时。在此，我们提出一种用于量子计量学的基于洛施密特回波的变分方案。通过在变分量子电路设计中使用硬件高效的量子态近似，探测态的量子费希尔信息（QFI）可以从实验测量的洛施密特回波中以可扩展的方式提取出来。然后，该QFI用于指导探测态制备的在线优化。我们在一个由10个自旋的量子处理器组成的系综上通过实验实现了该方案，并相对于不相关态实现了测量精度12.4分贝的提升，这接近理论极限。该方案还可以应用于各种其他有噪声的中尺度量子设备，这为证明量子优势提供了一个有前景的方案。
