Entanglement-enhanced optimal quantum metrology

TL;DR

This paper introduces an entanglement-enhanced quantum control scheme that improves the sensitivity of quantum metrology under noisy conditions, outperforming traditional unentangled approaches especially in complex Markovian and time-inhomogeneous noise environments.

Contribution

It presents a novel entanglement-based quantum optimal control method that enhances measurement precision under general Markovian and non-Markovian noise models.

Findings

Entanglement-enhanced scheme outperforms unentangled schemes under noise.

The protocol maintains high performance even with noisy ancillas.

Coherent control limitations are mitigated by entanglement in certain scenarios.

Abstract

Quantum optimal control (QOC) schemes can be employed to enhance the sensitivity of quantum metrology (QM) protocols undergoing Markovian noise, which can limit their precision to a standard quantum limit (SQL)-like scaling. In this paper, we propose a QOC scheme for QM that leverages entanglement and optimized coupling interactions with an ancillary system to provide enhanced metrological performance under general Markovian dynamics. We perform a comparative analysis of our entanglement-enhanced scheme against the unentangled scheme conventionally employed in QOC-enabled QM for varying evolution times and decoherence levels, revealing that the entanglement-enhanced scheme enables significantly better noise performance, even when a noisy ancilla is employed. We further extend our investigation to time-inhomogeneous noise models, specifically focusing on a noisy frequency estimation scenario within a spin-boson bath, and evaluate the protocol's performance under completely dissipative and dephasing dynamics. Our findings indicate that, in certain situations, schemes employing coherent control of a single particle are severely limited. In such cases, employing the entanglement-enhanced scheme can provide improved performance.