Materials Optimization for Low-Damping Magnons in Hybrid-Magnon Quantum Devices
Abstract: Magnons, also called spin waves, are collective excitations of spins in magnetic materials. They have intrinsic advantages for quantum information science and technology, such as microwave bandwidth, short wavelength (for device miniaturization) and nonreciprocity. Integrating magnetic materials into hybrid quantum systems has gained increased attention in recent years. One breakthrough from Tabuchi et al. (Science 349, 405 (2015)) demonstrated coherent coupling between a magnon and a superconducting qubit mediated by a microwave cavity, which opens possibility for magnons to transfer quantum information. Later in 2019, Li et al. (Phys. Rev. Lett. 123, 107701 (2019)) observed strong coupling between ferromagnetic permalloy thin film and a coplanar superconducting resonator, showing feasibility for all-on-chip hybrid magnon-photon platforms. One main challenge in the community is to reduce magnon damping such that the hybrid system can possess longer coherence. In this talk, I will discuss some perspectives on materials optimization for low-damping magnons. The direction of efforts depends on the material category. For the well-known low-damping ferrimagnetic insulator yttrium iron garnet (YIG), the main effort is to improve the material perfection with better fabrication strategy. For metallic ferromagnets, magnon-conduction electron scattering plays a dominant role. Therefore, any factor (such as temperature, doping, alloy composition, amorphization, etc.) that can affect electronic structure can in principle affect magnon damping as well. In this scenario, first-principles simulations, such as density functional theory (DFT), a powerful tool for calculating electronic structure of materials, can provide useful guidance for optimizing damping properties of materials. Some simulation results from our group will be presented.