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.

中文翻译：

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控制非Hermitian时间反转对称Floquet阶梯中的拓扑传输方向

我们提出了一种一维浮球梯，它具有两个不同的，方向相反的拓扑运输通道。发生运输通道的原因是${\mathbb{ž}}_2$受时间反转对称性保护的非Hermitian Floquet拓扑阶段。此阶段的特征是两对Kramers简并的Floquet准能带，它们之间的间隔是虚构的。我们讨论了如何在光子波导晶格中实现Floquet阶梯，并表明可以通过将两个光束聚焦到相邻的波导中来外部控制最终波导结构中的传输方向。两个光束之间的相对相位选择两个传输通道中的哪个为主，而两个光束的入射角确定非赫米特损耗抑制了哪个传输通道。