Quantum macroscopicity measure for arbitrary spin systems and its application to quantum phase transitions

TL;DR

This paper introduces a new measure for quantum macroscopicity applicable to any spin system and reveals large-scale superpositions during quantum phase transitions, advancing understanding of macroscopic quantum phenomena in many-body systems.

Contribution

A general, computable measure of quantum macroscopicity for arbitrary spin states is developed and applied to analyze quantum phase transitions.

Findings

Large macroscopic superpositions occur during quantum phase transitions.

The measure distinguishes between different quantum phenomena like superconductivity and superfluidity.

The approach enhances understanding of macroscopic quantum properties in many-body systems.

Abstract

We explore a previously unknown connection between two important problems in physics, i.e., quantum macroscopicity and the quantum phase transition. We devise a general and computable measure of quantum macroscopicity that can be applied to arbitrary spin states. We find that a macroscopic quantum superposition of an extremely large size arises during the quantum phase transition of the transverse Ising model in contrast to some seeming macroscopic quantum phenomena such as superconductivity, superfluidity and Bose-Einstein condensates. Our result may be an important step forward in understanding macroscopic quantum properties of many-body systems.