Physical significance of encircling absorbing exceptional points

Ascertain the physical significance of tuning the parameters of the four-port, three-mode cavity-magnonics platform (two inductively coupled transmission-line resonators each coupled to a common yttrium–iron–garnet Kittel magnon mode and driven by two independently phase- and amplitude-tunable microwave inputs) around a closed loop that encircles an absorbing exceptional point in the antimode spectrum, given that the eigenvectors associated with these absorbing exceptional points are not eigenstates of the full driven-dissipative system.

Background

The paper demonstrates interference-based exceptional points in a multi-drive cavity magnonics device, where antimodes (antiresonances) are associated with zeros of a submatrix of the scattering matrix and can be tuned via relative drive phase and amplitude. Unlike resonant exceptional points tied to poles of the full scattering matrix, these absorbing exceptional points arise in the antimode spectrum at a single output port and are linked to non-Hermitian degeneracies of an effective matrix describing antiresonances.

In conventional non-Hermitian systems, encircling resonant exceptional points can yield topological mode transfer. Here, however, the authors note that for absorbing exceptional points the relevant eigenvectors do not represent actual eigenstates of the full system, raising an unresolved question about the physical meaning and observable consequences of parameter loops around such points.