  The spin excitations of ordered magnets - magnons - mediate transport in
magnetic insulators. Their bosonic nature makes them qualitatively distinct
from electrons. These features include quantum properties traditionally
realized with photons. In this perspective, we present an intuitive discussion
of one such phenomenon. Equilibrium magnon-squeezing manifests unique
advantageous with magnons as compared to photons, including properties such as
entanglement. Building upon the recent progress in the fields of spintronics
and quantum optics, we outline challenges and opportunities in this emerging
field of quantum magnonics.
