The quasi-particle picture and its breakdown after local quenches: mutual information, negativity, and reflected entropy

TL;DR

This paper investigates the dynamics of quantum information measures after local excitations in conformal field theories, revealing a structure dependent on chaos and identifying the breakdown of the quasi-particle picture.

Contribution

It uncovers a conjectured structure linking mutual information, negativity, and reflected entropy in excited states, and distinguishes behaviors in integrable versus chaotic theories.

Findings

Quantum dimensions in RCFTs relate to all measures.

Correlation measures grow unbounded in theories with c > 1.

Breakdown of the quasi-particle picture in 2D CFTs is identified.

Abstract

We study the dynamics of (R\'enyi) mutual information, logarithmic negativity, and (R\'enyi) reflected entropy after exciting the ground state by a local operator. Together with recent results from Ref. [1], we are able to conjecture a close-knit structure between the three quantities that emerges in states excited above the vacuum, including both local and global quantum quenches. This structure intimately depends on the chaoticity of the theory i.e. there exist distinct sets of equivalences for integrable and chaotic theories. For rational conformal field theories (RCFT), we find all quantities to compute the quantum dimension of the primary operator inserted. In contrast, we find the correlation measures to grow (logarithmically) without bound in all $c > 1$ conformal field theories with a finite twist gap. In comparing the calculations in the two classes of theories, we are able to identify the dynamical mechanism for the breakdown of the quasi-particle picture in 2D conformal field theories. Intriguingly, we also find preliminary evidence that our general lessons apply to quantum systems considerably distinct from conformal field theories, such as integrable and chaotic spin chains, suggesting a universality of entanglement dynamics in non-equilibrium systems.