# Causal Emergence in Quantum Mechanics

## TL;DR

This paper demonstrates causal emergence in a quantum system, showing that a coarse-grained description can be more effective than a fine-grained one in predicting atomic positions in an interferometer.

## Contribution

It provides the first evidence of causal emergence in a quantum system, linking coarse-grained models to increased effectiveness over fine-grained models.

## Key findings

- Coarse-grained model predicts atomic positions more effectively.
- Quantum eraser measurements induce causal emergence.
- First demonstration of causal emergence in quantum mechanics.

## Abstract

Causal emergence is brought about when a coarse-grained description of a physical system is more effective (more deterministic and/or less degenerate) than the fine-grained corresponding model. We show, for the first time to our knowledge, a causal emergence in a quantum system: a atomic Mach-Zehnder interferometer with two which-path detectors. The atomic wave-like or particle-like descriptions are related, respectively, to \textit{coarse-grained} and \textit{fine-grained} models. The predictions of the atomic position after the passage through the interferometer when the to \textit{coarse-grained} description is considered are more effective than the corresponding \textit{fine-grained} model. We conclude that quantum eraser measurements yields the causal emergence in this system.