Classification of macroscopic quantum effects

TL;DR

This paper reviews experiments demonstrating quantum effects in large-scale systems, categorizes these systems based on key parameters, and proposes a theoretical framework for comparing their macroscopic quantum features.

Contribution

It provides a comprehensive classification of macroscopic quantum systems and introduces a theoretical basis for systematic comparison of their quantum properties.

Findings

Identified three broad classes of macroscopic quantum systems

Reviewed key experiments across different system types

Proposed a framework for quantifying macroscopic quantum features

Abstract

We review canonical experiments on systems that have pushed the boundary between the quantum and classical worlds towards much larger scales, and discuss their unique features that enable quantum coherence to survive. Because the types of systems differ so widely, we use a case by case approach to identifying the different parameters and criteria that capture their behaviour in a quantum mechanical framework. We find it helpful to categorise systems into three broad classes defined by mass, spatio-temporal coherence, and number of particles. The classes are not mutually exclusive and in fact the properties of some systems fit into several classes. We discuss experiments by turn, starting with interference of massive objects like macromolecules and micro-mechanical resonators, followed by self-interference of single particles in complex molecules, before examining the striking advances made with superconducting qubits. Finally, we propose a theoretical basis for quantifying the macroscopic features of a system to lay the ground for a more systematic comparison of the quantum properties in disparate systems.