Dynamics of entanglement in expanding quantum fields

TL;DR

This paper introduces a new real-time method for calculating entanglement entropy in quantum field theory, applied to an expanding geometry in the Schwinger model, revealing thermal-like behavior of entanglement in early times.

Contribution

It presents a novel real-time approach to entanglement in quantum fields and applies it to an expanding geometry, linking entanglement entropy to thermal properties in the Schwinger model.

Findings

Entanglement entropy becomes extensive in rapidity at early times.

The local reduced density matrix is thermal with a time-dependent temperature.

Results suggest a thermal interpretation of multiparticle production in e+ e- collisions.

Abstract

We develop a novel real-time approach to computing the entanglement between spatial regions for Gaussian states in quantum field theory. The entanglement entropy is characterized in terms of local correlation functions on space-like Cauchy hypersurfaces. The framework is applied to explore an expanding light cone geometry in the particular case of the Schwinger model for quantum electrodynamics in 1+1 space-time dimensions. We observe that the entanglement entropy becomes extensive in rapidity at early times and that the corresponding local reduced density matrix is a thermal density matrix for excitations around a coherent field with a time dependent temperature. Since the Schwinger model successfully describes many features of multiparticle production in $e^+ e^-$ collisions, our results provide an attractive explanation in this framework for the apparent thermal nature of multiparticle production even in the absence of significant final state scattering.