Emergence of classical realism under successive noncommuting measurements

TL;DR

This paper demonstrates that classical reality can emerge from quantum systems through successive monitoring of noncommuting observables, without relying on large reservoirs, by establishing elements of reality via a specific realism criterion.

Contribution

It introduces a mechanism for classicality emergence based on successive measurements of incompatible observables, expanding understanding beyond traditional decoherence models.

Findings

Classicality can emerge with a finite number of measurements.

Successive monitoring establishes elements of reality in quantum systems.

A quasi-classical regime is achievable for generic systems.

Abstract

The problem of emergence of classicality from quantum mechanics has been addressed over time through numerous frameworks, from Bohr's correspondence principle to quantum Darwinism. Traditional approaches associate the emergence of classicality with the decoherence process induced by large reservoirs on the system's state. In this work, we present an effective mechanism by which classicality emerges through the establishment of elements of reality. This involves the process of successive monitoring of noncommuting observables. To assess physical reality, we employ the realism criterion introduced by Bilobran and Angelo [EPL, 112 (2015) 40005], as well as their quantifier for the violations of this criterion. With these tools, we formally demonstrate, for generic systems, that a quasi-classical regime can always be reached with a sufficiently large number of incompatible measurements. Thus, instead of diagnosing the emergence of the classical regime in terms of the resulting algebraic characteristics for the density operator under the action of large reservoirs, our results reveal that classicality can emerge, at the level of physical elements of reality, from the coupling of the system with environments of a few degrees of freedom.