The Quantum Information of Cosmological Correlations

TL;DR

This paper investigates the quantum nature of cosmological correlations, showing that quantum discord quantifies the non-classical information retained after decoherence of primordial perturbations.

Contribution

It introduces quantum discord as a measure of the quantumness of cosmological correlations and models the system as a Gaussian state to analyze basis dependence.

Findings

Quantum discord captures non-classical correlations beyond entanglement.

Decoherence basis influences the quantum discord in cosmological perturbations.

Primordial information loss is quantified by the discord of the perturbations-environment system.

Abstract

It has been shown that the primordial perturbations sourced by inflation are driven to classicality by unitary evolution alone. However, their coupling with the environment such as photons and subsequent decoherence renders the cosmological correlations quantum, losing primordial information in the process. We argue that the quantumness of the resulting cosmological correlations is given by quantum discord, which captures non-classical behavior beyond quantum entanglement. By considering the environment as a quantum channel in which primordial information contained in the perturbations is transmitted to us, we can then ask how much of this information is inaccessible. We show that this amount of information is given by the discord of the joint primordial perturbations-environment system. To illustrate these points, we model the joint system as a mixed bi-modal Gaussian state, and show that quantum discord is dependent on the basis which decoherence occurs.