The Chern Number Governs Soliton Motion in Nonlinear Thouless Pumps

TL;DR

This paper demonstrates that the quantized motion of solitons in nonlinear Thouless pumps is governed by the Chern number of the underlying band, linking topological invariants to nonlinear soliton dynamics.

Contribution

It establishes a theoretical connection between the Chern number and soliton transport in nonlinear topological pumps, expanding understanding beyond linear band theory.

Findings

Transport is dictated by the Chern number for low power solitons.

Soliton position follows Wannier state throughout the pump cycle.

Describes soliton pumping in two-dimensional systems.

Abstract

Nonlinear Thouless pumps for bosons exhibit quantized pumping via soliton motion, despite the lack of a meaningful notion of filled bands. However, the theoretical underpinning of this quantization, as well as its relationship to the Chern number, has thus far been lacking. Here we show that for low power solitons, transport is dictated by the Chern number of the band from which the soliton bifurcates. We do this by expanding the discrete nonlinear Schr\"odinger equation (equivalently, the Gross-Pitaevskii equation) in the basis of Wannier states, showing that the soliton's position is dictated by that of the Wannier state throughout the pump cycle. Furthermore, we describe soliton pumping in two dimensions.