Controlling the direction of topological transport in a non-Hermitian time-reversal symmetric Floquet ladder

TL;DR

This paper introduces a non-Hermitian Floquet ladder with two topological transport channels of opposite directions, controllable via light beams, and demonstrates robustness against disorder in a photonic waveguide implementation.

Contribution

It presents a novel non-Hermitian Floquet topological phase with controllable transport directionality in a photonic system.

Findings

Two topological transport channels with opposite directions identified.

Transport direction can be externally controlled by light beam parameters.

Robustness of transport control demonstrated against disorder.

Abstract

We propose a one-dimensional Floquet ladder that possesses two distinct topological transport channels with opposite directionality. The transport channels occur due to a $\mathbb Z_2$ non-Hermitian Floquet topological phase that is protected by time-reversal symmetry. The signatures of this phase are two pairs of Kramers degenerate Floquet quasienergy bands that are separated by an imaginary gap. We discuss how the Floquet ladder can be implemented in a photonic waveguide lattice and show that the direction of transport in the resulting waveguide structure can be externally controlled by focusing two light beams into adjacent waveguides. The relative phase between the two light beams selects which of the two transport channels is predominantly populated, while the angles of incidence of the two light beams determine which of the transport channels is suppressed by non-Hermitian losses. We identify the optimal lattice parameters for the external control of transport and demonstrate the robustness of this mechanism against disorder.