Radical chiral Floquet phases in a periodically driven Kitaev model and beyond

TL;DR

This paper introduces radical chiral Floquet phases in a driven Kitaev model, revealing fractional topological indices and novel bulk-boundary dynamics involving anyon excitations, expanding the understanding of dynamical topological phases.

Contribution

It presents the concept of radical CF phases with fractional indices, constructs solvable models realizing these phases, and explores their stability and bulk-boundary correspondence.

Findings

Radical CF phases exhibit chiral indices as square roots of rational numbers.

External driving can pump non-Abelian defects, transporting fractional quantum information.

Bulk dynamics exchange electric and magnetic anyons during each period.

Abstract

Time periodic driving serves not only as a convenient way to engineer effective Hamiltonians, but also as a means to produce intrinsically dynamical phases that do not exist in the static limit. A recent example of the latter are 2D chiral Floquet (CF) phases exhibiting anomalous edge dynamics that pump discrete packets of quantum information along one direction. In non-fractionalized systems with only bosonic excitations, this pumping is quantified by a dynamical topological index that is a rational number -- highlighting its difference from the integer valued invariant underlying equilibrium chiral phases (e.g. quantum Hall systems). Here, we explore CF phases in systems with emergent anyon excitations that have fractional statistics (Abelian topological order). Despite the absence of mobile non-Abelian particles in these systems, external driving can supply the energy to pump otherwise immobile non-Abelian defects (sometimes called twist defects or genons) around the boundary, thereby transporting an irrational fractional number of quantum bits along the edge during each drive period. This enables new CF phases with chiral indices that are square roots of rational numbers, inspiring the label: "radical CF phases". We demonstrate an unexpected bulk-boundary correspondence, in which the radical CF edge is tied to bulk dynamics that exchange electric and magnetic anyon excitations during each period. We construct solvable, stroboscopically driven versions of Kitaev's honeycomb spin model that realize these radical CF phases, and discuss their stability against heating in strongly disordered many-body localized settings or in the limit of rapid driving as an exponentially long-lived pre-thermal phenomena.