Observing complex bound states in the spin-1/2 Heisenberg XXZ chain using local quantum quenches

TL;DR

This paper investigates non-equilibrium dynamics in the spin-1/2 XXZ Heisenberg chain after a local quench, revealing signatures of spinon and bound state excitations that persist beyond integrability, with implications for cold atom experiments.

Contribution

It demonstrates that local quantum quenches can effectively reveal bound states in the XXZ chain, even with integrability-breaking perturbations, providing a new approach to observe these states.

Findings

Strong signatures of spinon and bound state excitations observed

Bound states persist under integrability-breaking perturbations

Local quenches are effective probes for bound states in quantum spin chains

Abstract

We consider the non-equilibrium evolution in the spin-1/2 XXZ Heisenberg chain for fixed magnetization after a local quantum quench. This model is equivalent to interacting spinless fermions. Initially an infinite magnetic field is applied to n consecutive sites and the ground state is calculated. At time t=0 the field is switched off and the time evolution of observables such as the z-component of spin is computed using the Time Evolving Block Decimation (TEBD) algorithm. We find that the observables exhibit strong signatures of linearly propagating spinon and bound state excitations. These persist even when integrability-breaking perturbations are included. Since bound states ("strings") are notoriously difficult to observe using conventional probes such as inelastic neutron scattering, we conclude that local quantum quenches are an ideal setting for studying their properties. We comment on implications of our results for cold atom experiments.