Operational Resource Theory of Nonclassicality via Quantum Metrology

TL;DR

This paper introduces the first operational resource measure of nonclassicality in quantum states, directly linking it to quantum-enhanced precision in phase-space displacement measurements, with practical experimental implications.

Contribution

It develops a novel resource measure of nonclassicality that is operationally meaningful and directly related to quantum metrology performance, bridging theory and experiment.

Findings

The measure equals quantum enhancement for pure states.

It provides a tight upper bound for mixed states.

A simple interferometer can experimentally estimate the measure.

Abstract

The nonclassical properties of quantum states are of tremendous interest due to their potential applications in future technologies. It has recently been realized that the concept of a "resource theory" is a powerful approach to quantifying and understanding nonclassicality. To realize the potential of this approach one must first find resource theoretic measures of nonclassicality that are "operational", meaning that they also quantify the ability of quantum states to provide enhanced performance for specific tasks, such as precision sensing. Here we achieve a significant milestone in this endeavor by presenting the first such operational resource theoretic measure. In addition to satisfying the requirements of a resource measure, it has the closest possible relationship to the quantum-enhancement provided by a non-classical state for measuring phase-space displacement: it is equal to this enhancement for pure states, and is a tight upper bound on it for mixed states. We also show that a lower-bound on this measure can be obtained experimentally using a simple Mach-Zehnder interferometer.