A general framework for quantum macroscopicity in terms of coherence

TL;DR

This paper introduces a universal framework for quantifying macroscopic quantum coherence, linking it to resource theory and validating the quantum Fisher information as an effective measure.

Contribution

It develops a set of criteria for macroscopic coherence measures, connects them to resource theory, and evaluates existing measures against these criteria.

Findings

Quantum Fisher information effectively measures macroscopic coherence.

Some existing measures fail to meet the proposed criteria.

The framework unifies different approaches to macroscopicity.

Abstract

We propose a universal language to assess macroscopic quantumness in terms of coherence, with a set of conditions that should be satisfied by any measure of macroscopic coherence. We link the framework to the resource theory of asymmetry. We show that the quantum Fisher information gives a good measure of macroscopic coherence, enabling a rigorous justification of a previously proposed measure of macroscopicity. This picture lets us draw connections between different measures of macroscopicity and evaluate them; we show that another widely studied measure fails one of our criteria.