Dynamical phase transitions in quantum spin models with antiferromagnetic long-range interactions

TL;DR

This study investigates dynamical phase transitions in antiferromagnetic quantum spin chains with long-range interactions, revealing differences from ferromagnetic cases and connecting cusps in return rates to local order parameter dynamics.

Contribution

It provides a detailed analysis of dynamical phase transitions in antiferromagnetic long-range interacting spin models using advanced numerical methods, highlighting the absence of anomalous cusps and their relation to domain-wall binding.

Findings

Anomalous cusps are absent in antiferromagnetic cases within simulation timescales.

Regular cusps appear when quenching across the quantum critical point.

Long-range interactions alone do not guarantee anomalous cusps.

Abstract

In recent years, dynamical phase transitions and out-of-equilibrium criticality have been at the forefront of ultracold gases and condensed matter research. Whereas universality and scaling are established topics in equilibrium quantum many-body physics, out-of-equilibrium extensions of such concepts still leave much to be desired. Using exact diagonalization and the time-dependent variational principle in uniform martrix product states, we calculate the time evolution of the local order parameter and Loschmidt return rate in transverse-field Ising chains with antiferromagnetic power law-decaying interactions, and map out the corresponding rich dynamical phase diagram. \textit{Anomalous} cusps in the return rate, which are ubiquitous at small quenches within the ordered phase in the case of ferromagnetic long-range interactions, are absent within the accessible timescales of our simulations in the antiferromagnetic case, showing that long-range interactions are not a sufficient condition for their appearance. We attribute this to much weaker domain-wall binding in the antiferromagnetic case. For quenches across the quantum critical point, \textit{regular} cusps appear in the return rate and connect to the local order parameter changing sign, indicating the concurrence of two major concepts of dynamical phase transitions. Our results consolidate conclusions of previous works that a necessary condition for the appearance of anomalous cusps in the return rate after quenches within the ordered phase is for topologically trivial local spin flips to be the energetically dominant excitations in the spectrum of the quench Hamiltonian. Our findings are readily accessible in modern trapped-ion setups, and we outline the associated experimental considerations.