Quantum dimensions from local operator excitations in the Ising model

TL;DR

This paper investigates how local operator excitations in the critical Ising model influence entanglement measures, revealing connections to quantum dimensions and highlighting subtleties in conformal field theory correspondence.

Contribution

It demonstrates that entanglement evolution after local excitations encodes quantum dimensions and exposes discrepancies in operator identification between lattice models and conformal field theory.

Findings

Renyi entropies increase by the log of the quantum dimension for spin operators.

Small deviations occur for energy operators, indicating operator identification issues.

Universal features in entanglement evolution are observed away from criticality and with multiple excitations.

Abstract

We compare the time evolution of entanglement measures after local operator excitation in the critical Ising model with predictions from conformal field theory. For the spin operator and its descendants we find that Renyi entropies of a block of spins increase by a constant that matches the logarithm of the quantum dimension of the conformal family. However, for the energy operator we find a small constant contribution that differs from the conformal field theory answer equal to zero. We argue that the mismatch is caused by the subtleties in the identification between the local operators in conformal field theory and their lattice counterpart. Our results indicate that evolution of entanglement measures in locally excited states not only constraints this identification, but also can be used to extract non-trivial data about the conformal field theory that governs the critical point. We generalize our analysis to the Ising model away from the critical point, states with multiple local excitations, as well as the evolution of the relative entropy after local operator excitation and discuss universal features that emerge from numerics.