Novel Topology and Manipulation of Scattering Singularities in Complex non-Hermitian Systems

Abstract

The control of wave scattering in complex non-Hermitian settings is an exciting subject -- often challenging the creativity of researchers and stimulating the imagination of the public. Successful outcomes include invisibility cloaks, wavefront shaping protocols, active metasurface development, and more. At their core, these achievements rely on our ability to engineer the resonant spectrum of the underlying physical structures which is conventionally accomplished by carefully imposing geometrical and/or dynamical symmetries. In contrast, by taking active control over the boundary conditions in complex scattering environments which lack artificially-imposed geometric symmetries, we demonstrate via microwave experiments the ability to manipulate the spectrum of the scattering operator. This active control empowers the creation, destruction and repositioning of exceptional point degeneracies (EPD's) in a two-dimensional (2D) parameter space. The presence of EPD's signifies a coalescence of the scattering eigenmodes, which dramatically affects transport. The scattering EPD's are partitioned in domains characterized by a binary charge, as well as an integer winding number, are topologically stable in the two-dimensional parameter space, and obey winding number-conservation laws upon interactions with each other, even in cases where Lorentz reciprocity is violated; in this case the topological domains are destroyed. Ramifications of this understanding is the proposition for a unique input-magnitude and phase-insensitive 50:50 in-phase/quadrature (I/Q) power splitter. Our study establishes an important step towards complete control of scattering processes in complex non-Hermitian settings.

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• Coherent Perfect Absorbers: Time-reversed Lasers
• Observation of coherent perfect absorption at an exceptional point
• Exceptional Points in a Microwave Billiard with Time-Reversal Invariance Violation
• Observation of Chiral State Transfer Without Encircling an Exceptional Point
• Topological Modes in a Laser Cavity through Exceptional State Transfer
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Cited by in corpus (8)

• Ultrasensitive Higher-Order Exceptional Points via Non-Hermitian Zero-Index Materials
• A Physical Interpretation of Imaginary Time Delay
• Complex energy structures of exceptional point pairs in two level systems
• Arbitrary-Order Scattering Exceptional Points in Configurable Non-Hermitian Zero-Index Materials
• Joint control of coherent transmission, reflection, and absorption
• Superuniversal Statistics with Topological Origins for non-Hermitian Scattering Singularities
• Robust Wave Splitters Based on Scattering Singularities in Complex non-Hermitian Systems
• Universal Frequency Correlations and Recurrence Statistics of Complex Impedance Matrices