Nonlocal pseudospin dynamics in a quantum Ising chain

TL;DR

This paper explores how topological zero modes in a quantum Ising chain respond to Hermitian perturbations, revealing pseudospin dynamics and methods to identify quantum phases through quench experiments and Loschmidt echo measurements.

Contribution

It provides a pseudospin-based single-particle description of the response of topological zero modes to Hermitian perturbations in a quantum Ising chain.

Findings

String operators induce effective magnetic fields on pseudospin.

Quench dynamics can be used to probe degeneracy spectrum responses.

Loschmidt echo measurements help identify quantum phases.

Abstract

The existence of topological zero modes in nontrivial phase of quantum Ising chain results in not only the Kramers-like degeneracy spectrum, but also dynamic response for non-Hermitian perturbation in the ordered phase (2021 Phys. Rev. Lett. 126 116401). In this work, we investigate the possible response of the degeneracy spectrum for Hermitian perturbations. We provide a single-particle description of the model in the ordered phase, associating with an internal degree of freedom characterized as a pseudospin. The effective magnetic field, arising from both local and nonlocal perturbations in terms of string operators, acts on the pseudospin. We show that the action of string operator can be realized via a quench under the local perturbations. As an application, any ground states and excited states for the Hamiltonian with perturbation can be selected to identify the quantum phase, by adding the other perturbations to trigger a quench and measuring the Loschmidt echo.