  Magnons, the quanta of spin waves, could be used to encode information in
beyond-Moore computing applications, and magnonic device components, including
logic gates, transistors, and units for non-Boolean computing, have already
been developed. Magnonic directional couplers, which can function as circuit
building blocks, have also been explored, but have been impractical because of
their millimetre dimensions and multi-mode spectra. Here, we report a magnonic
directional coupler based on yttrium iron garnet single-mode waveguides of 350
nm width. We use the amplitude of a spin-wave to encode information and to
guide it to one of the two outputs of the coupler depending on the signal
magnitude, frequency, and the applied magnetic field. Using micromagnetic
simulations, we also propose an integrated magnonic half-adder that consists of
two directional couplers and processes all information within the magnon domain
with aJ energy consumption.
