Interpreting Quantum Discord in Quantum Metrology

TL;DR

This paper explores how quantum discord, a type of quantum correlation present even in nonentangled states, influences the precision of phase estimation in quantum metrology, providing a physical interpretation of this informational measure.

Contribution

It establishes a direct link between quantum discord and the minimum achievable precision in quantum interferometric phase estimation.

Findings

Quantum discord quantifies the lower bound of estimation precision.

Nonentangled states with quantum discord can outperform classical states in metrology.

Provides a physical interpretation of quantum discord in the context of quantum measurement.

Abstract

Multipartite quantum systems show properties which do not admit a classical explanation. In particular, even nonentangled states can enjoy a kind of quantum correlations called quantum discord. I discuss some recent results on the role of quantum discord in metrology. Given an interferometric phase estimation protocol where the Hamiltonian is initially unknown to the experimentalist, the quantum discord of the probe state quantifies the minimum precision of the estimation. This provides a physical interpretation to a widely investigated information-theoretic quantity.