Non-Hermitian scattering in Su-Schrieffer-Heeger superconducting waveguides: Exact Green's-function reduction and dimerization-sensitive microwave functionalities
Phys. Rev. A 113, 062466 – Published 29 June, 2026
DOI: https://doi.org/10.1103/kg2v-dsdn
Abstract
We formulate an exact Green's function theory for non-Hermitian single-microwave-photon scattering by finite superconducting circuit subsystems embedded in an Su-Schrieffer-Heeger (SSH) waveguide. The structured SSH environment is integrated out exactly and enters the local scattering problem as an energy-dependent matrix self-energy, reducing the full open system to a finite-dimensional effective non-Hermitian Hamiltonian. This reduction places scattering amplitudes, exceptional-point diagnostics, coherent-perfect-absorption conditions, and lasing thresholds within one unified framework. Within this approach we analyze two superconducting devices. A flux-controlled two-qubit interferometric scatterer exhibits a broad bright branch and a narrow quasidark branch whose interference is reshaped by the SSH environment and changes qualitatively across the two dimerizations. A mediator-assisted two-qubit scatterer generates an additional energy-dependent complex coupling, reorganizes the dressed spectrum, and produces clearer dimerization-sensitive transparency-versus-absorption windows together with a pronounced separation between zerolike and polelike scattering branches. In the active regime, near-exceptional-point hybridization enhances the pole-dominated response while deepening the singular-value valley associated with near-coherent perfect absorption. These results show how structured topological waveguides can be used not only to host scattering but also to design non-Hermitian superconducting microwave functionalities.
