  At filling factor $\nu=0,\pm1$, the ground state of graphene is a particular
SU(4) ferromagnet which hosts a rich phase diagram along with several spin,
pseudospin or "entanglement" magnon modes. Motivated by recent experiments, we
study a $\nu=-1|0|-1$ Fabry-P\'erot magnonic junction. If the ground state at
$\nu=0$ is spin polarized, there exist two spin modes which interfere and
create a beating pattern, while pseudospin modes are reflected. The same
scenario occurs for pseudospin magnon if the $\nu=0$ ground state is pseudospin
polarized. The observation of such an interference pattern would provide
information on the low-energy anisotropies and thus on the ground state.
