Quasiparticle origin of dynamical quantum phase transitions

TL;DR

This paper links quasiparticle excitations to nonanalyticities in the Loschmidt return rate in quantum Ising chains, showing how bound domain walls cause anomalous cusps, revealing new out-of-equilibrium critical phenomena.

Contribution

It demonstrates the connection between quasiparticle bound states and dynamical quantum phase transitions in nonintegrable quantum chains, highlighting differences from integrable models.

Findings

Bound domain walls lead to anomalous cusps in the return rate.

Nearest-neighbor models lack anomalous cusps due to freely propagating domain walls.

Models in the same equilibrium class can show different out-of-equilibrium criticality.

Abstract

Considering nonintegrable quantum Ising chains with exponentially decaying interactions, we present matrix product state results that establish a connection between low-energy quasiparticle excitations and the kind of nonanalyticities in the Loschmidt return rate. When domain walls in the spectrum of the quench Hamiltonian are energetically favored to be bound rather than freely propagating, anomalous cusps appear in the return rate regardless of the initial state. In the nearest-neighbor limit, domain walls are always freely propagating, and anomalous cusps never appear. As a consequence, our work illustrates that models in the same equilibrium universality class can still exhibit fundamentally distinct out-of-equilibrium criticality. Our results are accessible to current ultracold-atom and ion-trap experiments.