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 $\mathbf{S}$ and momentum $\mathbf{q}$ of microwaves emitted by an excited magnetic particle are locked by $\mathbf{q}\ensuremath{\cdot}\mathbf{S}=0$ with a fixed chirality $\stackrel{^}{\mathbf{n}}\ensuremath{\cdot}(\stackrel{^}{\mathbf{S}}\ifmmode\times\else\texttimes\fi{}\stackrel{^}{\mathbf{q}})=1$ when evanescent along $\stackrel{^}{\mathbf{n}}\ensuremath{\perp}\mathbf{q}$. 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.