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Nonlinear tuning of PT symmetry and non-Hermitian topological states

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Science  02 Apr 2021:
Vol. 372, Issue 6537, pp. 72-76
DOI: 10.1126/science.abf6873

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Nonlinear control of topology

Controlling the topological properties of physical systems provides a platform for developing devices and technology that are robust to defects. Xia et al. present a photonic platform in which the underlying dynamics are driven and tuned by the interplay among topology, non-Hermiticity, and nonlinearity (see the Perspective by Roztocki and Morandotti). Using photonic lattices consisting of laser-written waveguides that are continuous (“gain”) and sectioned (“loss”) and coupled to an interface defect, they demonstrate the nonlinear control of parity-time symmetry and nonlinearity-induced restoration and/or destruction of non-Hermitian topological states. Such concepts are applicable to a broad spectrum of non-Hermitian systems that have intensity-dependent gain or loss and may enable new approaches for light manipulation.

Science, this issue p. 72; see also p. 32

Abstract

Topology, parity-time (PT) symmetry, and nonlinearity are at the origin of many fundamental phenomena in complex systems across the natural sciences, but their mutual interplay remains unexplored. We established a nonlinear non-Hermitian topological platform for active tuning of PT symmetry and topological states. We found that the loss in a topological defect potential in a non-Hermitian photonic lattice can be tuned solely by nonlinearity, enabling the transition between PT-symmetric and non–PT-symmetric regimes and the maneuvering of topological zero modes. The interaction between two apparently antagonistic effects is revealed: the sensitivity close to exceptional points and the robustness of non-Hermitian topological states. Our scheme using single-channel control of global PT symmetry and topology via local nonlinearity may provide opportunities for unconventional light manipulation and device applications.

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