Hybrid quantum-classical approach to enhanced quantum metrology

Xiaodong Yang, Xi Chen, Jun Li, Xinhua Peng, Raymond Laflamme

Published 2020-08-14Version 1

Quantum metrology plays a fundamental role in many scientific areas, and it concerns how to manipulate the given resources to achieve the best precision of the to-be-estimated parameter. Usually, the highest precision can be reached by performing optimal probe states and the corresponding optimal measurements under prefixed dynamics. However, the complexity of engineering entangled probes and the external noise raise technological barriers for its realization. Here, we address this problem by introducing adjustable controls into the encoding process and then utilizing a hybrid quantum-classical approach to automatically optimize the controls online. Our scheme does not require any complex or intractable off-line design, and it can inherently correct certain errors during the learning procedure. We also report the first experimental demonstration of this promising scheme for the task of frequency estimation on a nuclear magnetic resonance (NMR) processor. The proposed scheme paves the way to experimentally auto-search optimal protocol for improving the metrology precision.