Quench spectroscopy of amplitude modes in a one-dimensional critical phase

TL;DR

This paper reveals a symmetry-preserving amplitude mode in a one-dimensional XXZ spin chain, detectable via quench spectroscopy, expanding understanding of collective excitations in quantum many-body systems.

Contribution

It identifies a novel amplitude mode in a gapless phase without symmetry breaking using quench spectroscopy and Bethe-ansatz analysis.

Findings

Amplitude mode observed as oscillations in U(1)-symmetric observables

Mode traced to specific string excitations via Bethe-ansatz

Potential detection in quantum magnets and simulators

Abstract

We investigate the emergence of an amplitude (Higgs-like) mode in the gapless phase of the $(1+1)$D XXZ spin chain. Unlike conventional settings where amplitude modes arise from spontaneous symmetry breaking, here, we identify a symmetry-preserving underdamped excitation on top of a Luttinger-liquid ground state. Using nonequilibrium quench spectroscopy, we demonstrate that this mode manifests as oscillations of U(1)-symmetric observables following a sudden quench. By combining numerical simulations with Bethe-ansatz analyses, we trace its microscopic origin to specific families of string excitations. We further discuss experimental pathways to detect this mode in easy-plane quantum magnets and programmable quantum simulators. Our results showcase the utility of quantum quenches as a powerful tool to probe collective excitations, beyond the scope of linear response.