Emergence of classical realism under successive noncommuting measurements

Department of Physics, Federal University of Paraná - P. O. Box 19044, 81531-980 Curitiba, PR, Brazil

Received: 19 November 2024
Accepted: 24 March 2025

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 (see Bilobran A. L. O. and Angelo R. M., 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.