The full coherent control of hybridized systems such as strongly coupled cavity photon-magnon states is a crucial step to enable future information processing technologies. Thus, it is particularly interesting to engineer deliberate control mechanisms such as the full control of the coupling strength as a measure for coherent information exchange. In this work, we employ cavity resonator spectroscopy to demonstrate the complete control of the coupling strength of hybridized cavity photon-magnon states. For this, we use two driving microwave inputs which can be tuned at will. Here, only the first input couples directly to the cavity resonator photons, whilst the second tone exclusively acts as a direct input for the magnons. For these inputs, both the relative phase φ and amplitude δ0 can be independently controlled. We demonstrate that for specific quadratures between both tones we can increase the coupling strength, close the anticrossing gap, and enter a regime of level merging. At the transition, the total amplitude is enhanced by a factor of 1000 and we observe an additional linewidth decrease of 13% at resonance due to level merging. Such control of the coupling, and hence linewidth, open up an avenue to enable or suppress an exchange of information and bridging the gap between quantum information and spintronics applications.Polaritons are the quasiparticles associated with the coupling of electromagnetic waves with an excited state of matter [1,2]. Such hybridized systems are promising candidates for applications as they can combine the advantages of the different physical systems and overcome the limitations of a single one [3][4][5]. While hybrid quantum circuits represent a tool for the deliberate control of quantum states, light-matter interactions can be thought as an equivalent for macroscopic systems through various types of polaritons such as exciton-photon, or magnon polaritons (MPs) [6][7][8][9][10][11][12][13]. For instance, MPs enable examining the spin-photon interaction, where the magnons are the associated quanta of a collective spin excitation [14]. Thus, the study and manipulation of spin-photon interaction could lead to the development of spintronic applications [15][16][17][18][19][20]. However, the realization of applications based on such hybrid systems also requires full control over the coupling strength g eff which is a measure for the coherent exchange of information. Therefore, such control would enable a deliberate enhancement or suppression of the information exchange [21]. This is of broad interest, and has been studied for various systems such as single atoms, optomechanical circuits, exciton or surface plasmon polaritons, and quantum dots strongly coupled to a nanocavity [22][23][24][25][26].

Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of current challenges and the outlook of further development for each research direction.

Science and Technology, NO-7491 Trondheim, Norway ‡ These two authors contribute equally to this work Keywords: Magnetic insulator, SOT switching, Dzyaloshinskii-Moriya interaction, Chiral domain wall, Skyrmion. The interfacial Dzyaloshinskii-Moriya interaction (DMI) in multilayers of heavy metal and ferromagnetic metals enables the stabilization of novel chiral spin structures such as skyrmions. Magnetic insulators, on the other hand can exhibit enhanced dynamics and properties such as lower magnetic damping and therefore it is of interest to combine the properties enabled by interfacial DMI with insulating systems. Here, we demonstrate the presence of interfacial DMI in heterostructures that include insulating magnetic layers. We use a bilayer of perpendicularly magnetized insulating thulium iron garnet (TmIG) and the heavy metal platinum, and find a surprisingly strong interfacial DMI that, combined with spin-orbit torque results, in efficient switching. The interfacial origin is confirmed through thickness dependence measurements of the DMI, revealing the characteristic 1/thickness dependence with one order of magnitude longer decay length compared to metallic layers. We combine chiral spin structures and spinorbit torques for efficient switching and identify skyrmions that allow us to establish the GGG/TmIG interface as the origin of the DMI.The Dzyaloshinskii-Moriya interaction (DMI), an asymmetric exchange interaction, has been intensely studied due to the formation of chiral spin textures such as magnetic