Quantum entanglement and entropy in particle creation

TL;DR

This paper explores how quantum entanglement and entropy in particle creation depend on measurement choices and background dynamics, highlighting the importance of variable selection in understanding entanglement and entropy generation.

Contribution

It provides a theoretical analysis of entanglement in particle creation, emphasizing the dependence on physical variables and background spacetime, with explicit examples in cosmology.

Findings

Entanglement entropy varies with the choice of physical variables.

Different variable choices lead to different measures of entropy.

Application to cosmological particle production shows the role of particle number and phase.

Abstract

We investigate the basic theoretical issues in the quantum entanglement of particle pairs created from the vacuum in a time-dependent background field or spacetime. Similar to entropy generation from these processes which depends on the choice of physical variables and how certain information is coarse-grained, entanglement dynamics hinges on the choice of measurable quantities and how the two parties are selected as well as the background dynamics of the field or spacetime. We discuss the conditions of separability of quantum states in particle creation processes and point out the differences in how the von Neumann entropy is used as a measure of entropy generation versus for entanglement dynamics. We show by an explicit construction that adoption of a different set of physical variables yields a different entanglement entropy. As an application of these theoretical considerations we show how the particle number and the quantum phase enter the entanglement dynamics in cosmological particle production.