Unification of Exceptional Points and Transmission Peak Degeneracies in a Highly Tunable Magnon-Photon Dimer (2506.09141v2)

Abstract: Exceptional points (EPs), spectral singularities arising in non-Hermitian dynamical systems, have drawn widespread attention for their potential to enhance sensor capability by leveraging characteristic square-root frequency splitting. However, the advantages of EP sensors have remained highly contested, primarily due to their inherent hypersensitivity to model errors and loss of precision arising from eigenbasis collapse, quantified by the Petermann noise factor. Recently, it has been suggested that practical sensor implementations should instead utilize transmission peak degeneracies (TPDs), which exhibit square-root transmission splitting while maintaining a complete eigenbasis, potentially mitigating the Petermann noise around EPs. This work presents a microwave magnon-photon dimer with near-universal tunability across all relevant parameters, which we use to investigate various TPDs experimentally. We demonstrate that two-dimensional EP and TPD configurations based on coupled oscillators can be unified into a general theory and experimental framework utilizing synthetic gauge fields, which we present and validate through careful experiments on two representative TPDs. We also introduce practical metrics to quantify the performance and robustness of TPDs beyond just the Petermann noise factor. Our formalism and experimental methods unify previous EP and TPD configurations and may lead to the realization of robust TPD-enhanced sensors.