Spin-orbit-locked coupling of localized microwaves to magnons

We address the photonic spin-orbit coupling known from nano-optics and plasmonics in the microwave regime. The spin S and momentum q of microwaves emitted by an excited magnetic particle are locked by q⋅S=0 with a fixed chirality n^⋅(S^×q^)=1 when evanescent along n^⊥q. This field excites magnons in a nearby magnetic film in the form of directional beams that rotate with the magnetization direction. The exchange of these magnons between two distant nanomagnets leads to a highly tunable strong coupling and entangles their excited states.