Quasi-normal modes empowered coherent control of electromagnetic interactions

Quasi-normal modes (QNMs) and coherent control of light-matter interactions (through synchronized multiple coherent incident waves) are profound and pervasive concepts in and beyond photonics, making accessible photonic manipulations with extreme precision and efficiency. Though each has been playing essential roles in its own, these two sweeping concepts remain largely segregated with little interactions, blocking vast opportunities of cross-fertilization to explore. Here we unify both concepts into a novel framework of coherent control for light interacting with open photonic systems. From the QNM perspective, scattered waves are superimposed radiations from all QNMs excited, and thus coherent controls can be mapped into another problem of QNM excitation manipulations. Within our framework, all incident properties (amplitudes, phases and polarizations) of waves from different directions can be exploited simultaneously in a synchronous manner, facilitating independent manipulations of each QNM and thus unlocking enormous flexibilities for coherent controls of both scattering intensity and polarization: (i) A visible structure under a single incident wave can be made invisible through shining extra waves; (ii) Along a direction where QNMs' radiation polarizations are identical, scattering along this direction can be fully eliminated, thus generalizing Kerker effects from a distinct QNM perspective; (iii) Along a direction of distinct QNM radiation polarizations, arbitrary scattering polarizations can be obtained. Given the ubiquity and profundity of QNMs and coherent control in almost all branches of wave physics, our framework and its underlying principles will inspire further fundamental explorations and practical applications beyond photonics, opening new opportunities for various forms of wave-matter interactions.