Variational-State Quantum Metrology

TL;DR

This paper introduces a variational approach to identify near-optimal quantum states for metrology under noise, demonstrating significant advantages over known states through extensive simulations of up to 9 qubits.

Contribution

It develops a novel variational method to find highly entangled, non-symmetric states for quantum metrology, outperforming previous states under noise conditions.

Findings

Discovered new entangled states outperforming known states by up to a factor of 2.

Demonstrated quantum advantage persists under various noise models.

Proposed an experimental setup suitable for near-term quantum hardware.

Abstract

Quantum technologies exploit entanglement to enhance various tasks beyond their classical limits including computation, communication and measurements. Quantum metrology aims to increase the precision of a measured quantity that is estimated in the presence of statistical errors using entangled quantum states. We present a novel approach for finding (near) optimal states for metrology in the presence of noise, using variational techniques as a tool for efficiently searching the classically intractable high-dimensional space of quantum states. We comprehensively explore systems consisting of up to 9 qubits and find new highly entangled states that are not symmetric under permutations and non-trivially outperform previously known states up to a constant factor 2. We consider a range of environmental noise models; while passive quantum states cannot achieve a fundamentally superior scaling (as established by prior asymptotic results) we do observe a significant absolute quantum advantage. We finally outline a possible experimental setup for variational quantum metrology which can be implemented in near-term hardware.