Light-cone and local front dynamics of a single-particle extended quantum walk

Abstract

We study the light-cone and front dynamics of a single-particle continuous time extended quantum walk on a one-dimensional lattice with finite range hopping. We show that, in general, for an initially localized state, propagating wave fronts can be characterized as ordinary or extremal fronts with the latter exhibiting an anomalous subdiffusive scaling behavior in the front region. We investigate the dynamical global and local scaling properties of the cumulative probability distribution function for the extended walk with nearest- and next-nearest-neighbor hopping using analytical and numerical methods. The global scaling shows the existence of a ``causal light-cone'' corresponding to excitations traveling with a velocity smaller than a maximal ``light velocity.'' Maximal fronts moving with fixed light velocity bound the causal cone. The front regions spread with time subdiffusively exhibiting a local Airy scaling which leads to an internal staircase structure. At a certain critical next-nearest-neighbor hopping strength, there is a transition from a phase with one `causal cone' to a phase with two nested `causal cones' and the existence of an internal staircase structure in the corresponding cumulative distribution profiles. We also connect the study to that in spin chain systems and indicate that a single-particle quantum walk on the one-dimensional lattice already captures the many-body physics of a spin chain system. In particular, we suggest that the time evolution of a single-particle quantum walk on the one-dimensional lattice with an initially localized state is equivalent to the time evolution of a domain-wall initial state in a corresponding spin chain system.