Variational quantum state preparation for quantum-enhanced metrology in noisy systems

TL;DR

This paper explores how to optimize quantum state preparation in noisy environments for enhanced quantum metrology, identifying key state regimes that maximize sensitivity despite dephasing noise.

Contribution

It introduces a variational quantum circuit approach optimized for noisy conditions and classifies resulting states into three main regimes based on dephasing rates.

Findings

Optimal states are categorized into three regimes: cat-like, squeezed-like, and product states.

The VQC parameters can be tuned to maximize quantum Fisher information under noise.

Results inform design of quantum sensors resilient to dephasing noise.

Abstract

We investigate optimized quantum state preparation for quantum metrology applications in noisy environments. Using the QFI-Opt package, we simulate a low-depth variational quantum circuit (VQC) composed of a sequence of global rotations and entangling operations applied to a chain of qubits that are subject to dephasing noise. The parameters controlling the VQC are numerically optimized to maximize the quantum Fisher information, which characterizes the ultimate metrological sensitivity of a quantum state with respect to a global rotation. We find that regardless of the details of the entangling operation implemented in the VQC, the optimal quantum states can be broadly classified into a trio of qualitative regimes--cat-like, squeezed-like, and product states--associated with different dephasing rates. Our findings are relevant for designing optimal state-preparation strategies for next-generation quantum sensors exploiting entanglement, such as time and frequency standards and magnetometers, aimed at achieving state-of-the-art performance in the presence of noise and decoherence.