Unambiguous scattering matrix for non-Hermitian systems

@article{Novitsky2020UnambiguousSM,
  title={Unambiguous scattering matrix for non-Hermitian systems},
  author={Andrey Novitsky and Dmitry A. Lyakhov and Dominik Ludewig Michels and Alexander A. Pavlov and Alexander S. Shalin and Denis V. Novitsky},
  journal={Physical Review A},
  year={2020}
}
$\mathcal{PT}$ symmetry is a unique platform for light manipulation and versatile use in unidirectional invisibility, lasing, sensing, etc. Broken and unbroken $\mathcal{PT}$-symmetric states in non-Hermitian open systems are described by scattering matrices. A multilayer structure, as a simplest example of the open system, has no certain definition of the scattering matrix, since the output ports can be permuted. The uncertainty in definition of the exceptional points bordering $\mathcal{PT… 

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