Coherence Based Characterization of Macroscopic Quantumness

TL;DR

This paper introduces a coherence-based measure to characterize macroscopic quantumness, providing a first-principles framework to understand the quantum-to-classical transition and identify states like GHZ and NOON as maximally quantum.

Contribution

It proposes a novel measure of macroscopic coherence rooted in first principles, enhancing understanding of macroscopic quantum states and their role in the quantum-classical boundary.

Findings

The measure quantifies the collective coherence of quantum states.

GHZ and NOON states are identified as states that maximize this measure.

The approach offers insights into the quantum-to-classical transition.

Abstract

One of the most elusive problems in quantum mechanics is the transition between classical and quantum physics. This problem can be traced back to the Schr\"{o}dinger's cat. A key element that lies at the center of this problem is the lack of a clear understanding and characterization of macroscopic quantum states. Our understanding of Macroscopic Quantumness relies on states such as the Greenberger-Horne-Zeilinger(GHZ) or the NOON state. Here we take a first principle approach to this problem. We start from coherence as the key quantity that captures the notion of quantumness and demand the quantumness to be collective and macroscopic. To this end, we introduce macroscopic coherence which is the coherence between macroscopically distinct quantum states. We construct a measure that quantifies how global and collective the coherence of the state is. Our work also provides a first-principle way to derive well-established states like the GHZ and the NOON state as the states that maximize our measure. This new approach paves the way towards a better understanding of the Quantum-to-Classical transition.