Title: Higher-order scattering phenomena in generic complex non-Hermitian systems
Abstract: Multi-port scattering systems have many interesting phenomena and allow for unique applications not possible in two-port systems. We show that there is an abundance of topologically protected singularities that exist in generic complex scattering systems and that they are easily manipulatable with tunable parameters.
We demonstrate that with just a few tunable parameters we are able to create the conditions for nearly any scattering singularity at arbitrary frequencies in these systems. With five tunable parameters, we demonstrate that more complex scenarios can be accomplished, such as creating coincident singularities in parameter space or placing singularities at different frequencies under the same system conditions.
A benefit of this approach is that a generic system can be manipulated into exhibiting numerous different phenomena solely by reconfiguring its tunable parameters. A particularly interesting scattering phenomenon is coherent perfect absorption, where a specific wavefront injected into the system is completely absorbed with no reflection or transmission. After creating the conditions for this singularity, we can find and inject the coherent perfect absorption wavefront into a multi-port quarter bowtie billiard and demonstrate a near complete absorption of the input wavefront.