Classical and Quantum Correlations of Scalar Field in the Inflationary Universe

TL;DR

This paper studies how quantum and classical correlations of a scalar field evolve during inflation, showing that entanglement and quantum discord diminish beyond the Hubble horizon, indicating a transition to classicality.

Contribution

It provides a detailed analysis of the decay of quantum correlations in an inflationary universe using a particle detector model, highlighting the emergence of classical behavior.

Findings

Entanglement vanishes beyond the Hubble horizon.

Quantum discord approaches zero on super horizon scales.

Supports the classical nature of inflationary quantum fluctuations.

Abstract

We investigate classical and quantum correlations of a quantum field in the inflationary universe using a particle detector model. By considering the entanglement and correlations between two comoving detectors interacting with a scalar field, we find that the entanglement between the detectors becomes zero after their physical separation exceeds the Hubble horizon. Furthermore, the quantum discord, which is defined as the quantum part of total correlation, approaches zero on super horizon scale. These behaviors support appearance of classical nature of the quantum fluctuation generated during the inflationary era.