Emergence of Objectivity for Quantum Many-Body Systems

TL;DR

This paper investigates how classical objectivity emerges in quantum many-body systems without an environment, showing that under certain conditions, multiple observers can reliably access consistent classical information.

Contribution

It extends previous results to mixed states and imperfect measurements, introducing new conditions for classicality and demonstrating their natural emergence in quantum dynamics.

Findings

Conditions for classicality are satisfied in many quantum evolutions.

Redundant measurement outcomes lead to classical objectivity.

Theoretical framework applies to mixed states and POVMs.

Abstract

We examine the emergence of objectivity for quantum many-body systems in a setting without an environment to decohere the system's state, but where observers can only access small fragments of the whole system. We extend the result of Reidel (2017) to the case where the system is in a mixed state, measurements are performed through POVMs, and imprints of the outcomes are imperfect. We introduce a new condition on states and measurements to recover full classicality for any number of observers. We further show that evolutions of quantum many-body systems can be expected to yield states that satisfy this condition whenever the corresponding measurement outcomes are redundant.