Entanglement evolution after a global quench across a conformal defect

TL;DR

This paper investigates how entanglement entropy evolves after a global quench in a one-dimensional quantum system with a conformal defect, revealing linear growth and relating it to an effective central charge, with comparisons between field theory and lattice models.

Contribution

It introduces boundary twist fields to connect entanglement growth to effective central charge and compares analytical predictions with lattice model results.

Findings

Entanglement entropy grows linearly after a quench across a conformal defect.

The slope of growth relates to an effective central charge.

Discrepancies exist between field theory and lattice results, even as the gap vanishes.

Abstract

We study the evolution of entanglement after a global quench in a one-dimensional quantum system with a localized impurity. For systems described by a conformal field theory, the entanglement entropy between the two regions separated by the defect grows linearly in time. Introducing the notion of boundary twist fields, we show how the slope of this growth can be related to the effective central charge that emerges in the study of ground-state entropy in the presence of the defect. On the other hand, we also consider a particular lattice realization of the quench in a free-fermion chain with a conformal defect. Starting from a gapped initial state, we obtain the slope via a quasiparticle ansatz and observe small discrepancies between the field theory and lattice results, which persist even in the limit of a vanishing gap.