# Emerging dynamics arising from coarse-grained quantum systems

## TL;DR

This paper investigates how coarse-grained quantum systems exhibit emergent dynamics, revealing that effective descriptions can deviate from standard forms and may include non-Markovian features, with implications for thermalization and measurement processes.

## Contribution

It introduces a framework for understanding the dynamics of coarse-grained quantum systems, highlighting non-Kraus maps and potential increases in state distinguishability.

## Key findings

- Effective maps can deviate from Kraus form due to correlations.
- Distance between states may increase under effective dynamics.
- Framework applicable to quantum thermalization and measurement analysis.

## Abstract

The purpose of physics is to describe nature from elementary particles all the way up to cosmological objects like cluster of galaxies and black holes. Although a unified description for all this spectrum of events is desirable, this would be highly impractical. To not get lost in unnecessary details, effective descriptions are mandatory. Here we analyze the dynamics that may emerge from a full quantum description when one does not have access to all the degrees of freedom of a system. More concretely, we describe the properties of the dynamics that arise from quantum mechanics if one has access only to a coarse-grained description of the system. We obtain that the effective maps are not necessarily of Kraus form, due to correlations between accessible and nonaccessible degrees of freedom, and that the distance between two effective states may increase under the action of the effective map. We expect our framework to be useful for addressing questions such as the thermalization of closed quantum systems, as well as the description of measurements in quantum mechanics.