How many lives does Schr\"odinger's cat have?

TL;DR

This paper explores the concept of macroscopic quantum superpositions, using Schr"odinger's cat as a pedagogical tool to explain measures, experiments, and their relevance to quantum metrology.

Contribution

It provides a comprehensive, pedagogical overview of macroscopicity in quantum systems, including visualizations and a hands-on activity for educational purposes.

Findings

Introduction of macroscopicity measures

Description of experimental realizations

Connection to quantum metrology

Abstract

Schr\"odinger's cat is an iconic example for the problem of the transition from the microscopic quantum world to the macroscopic, classical one. It opened many interesting questions such as, could a macroscopic superposition like a dead and alive cat ever exist? What would be the characteristic features of such a system? The field of macroscopicity aims at providing answers to those questions, both from a theoretical and an experimental point of view. Here, we present the main concepts in macroscopicity, including macroscopicity measures, experimental realizations and the link to metrology, from a pedagogical perspective. We provide visualizations and intuitive explanations, together with a hands-on activity where students can create their own macroscopic quantum cats from cardboard cells that are in a superposition of being dead and alive.