Coherent states and the classical-quantum limit considered from the point of view of entanglement

TL;DR

This paper explores how coherent states serve as classical pointer states in quantum systems, especially in regimes where particles interact without entanglement, shedding light on the quantum-classical transition and decoherence.

Contribution

It demonstrates that under general conditions, coherent states naturally emerge as classical states due to their entanglement-free interactions with the environment.

Findings

Coherent states do not entangle with the environment when exchanging one quantum at a time.

The entanglement-free regime models classical islands and preferred bases in decoherence.

Bosonic symmetry plays a key role in the classicality of coherent states.

Abstract

Three paradigms commonly used in classical, pre-quantum physics to describe particles (that is: the material point, the test-particle and the diluted particle (droplet model)) can be identified as limit-cases of a quantum regime in which pairs of particles interact without getting entangled with each other. This entanglement-free regime also provides a simplified model of what is called in the decoherence approach "islands of classicality", that is, preferred bases that would be selected through evolution by a Darwinist mechanism that aims at optimising information. We show how, under very general conditions, coherent states are natural candidates for classical pointer states. This occurs essentially because, when a (supposedly bosonic) system coherently exchanges only one quantum at a time with the (supposedly bosonic) environment, coherent states of the system do not get entangled with the environment, due to the bosonic symmetry.