Quantum discord determines the interferometric power of quantum states

TL;DR

This paper demonstrates that quantum discord quantifies the worst-case precision in quantum interferometric sensing, with experimental validation showing discordant states outperform classically correlated ones in parameter estimation.

Contribution

It introduces a new measure linking quantum discord to interferometric sensing performance and provides the first experimental proof of discord's role in quantum metrology.

Findings

Quantum discord determines the worst-case precision in quantum interferometry.

Discordant states enable nonzero estimation precision across various Hamiltonians.

Classically correlated states fail to guarantee estimation in the worst-case scenario.

Abstract

Quantum metrology exploits quantum mechanical laws to improve the precision in estimating technologically relevant parameters such as phase, frequency, or magnetic fields. Probe states are usually tailored on the particular dynamics whose parameters are being estimated. Here we consider a novel framework where quantum estimation is performed in an interferometric configuration, using bipartite probe states prepared when only the spectrum of the generating Hamiltonian is known. We introduce a figure of merit for the scheme, given by the worst case precision over all suitable Hamiltonians, and prove that it amounts exactly to a computable measure of discord-type quantum correlations for the input probe. We complement our theoretical results with a metrology experiment, realized in a highly controllable room-temperature nuclear magnetic resonance setup, which provides a proof-of-concept demonstration for the usefulness of discord in sensing applications. Discordant probes are shown to guarantee a nonzero precision in the estimation procedure for different generating Hamiltonians, while classically correlated probes are unable to accomplish the estimation in a worst case setting. This work establishes a rigorous and direct operational interpretation for general quantum correlations, shedding light on their potential for quantum technology.