  We show how a quantum state in a microwave cavity mode can be transferred to
and stored in a phononic mode via an intermediate magnon mode in a
magnomechanical system. For this we consider a ferrimagnetic yttrium iron
garnet (YIG) sphere inserted in a microwave cavity, where the microwave and
magnon modes are coupled via a magnetic-dipole interaction and the magnon and
phonon modes in the YIG sphere are coupled via magnetostrictive forces. By
modulating the cavity and magnon detunings and the driving of the magnon mode
in time, a Stimulated Raman Adiabatic Passage (STIRAP)-like coherent transfer
becomes possible between the cavity mode and the phonon mode. The phononic mode
can be used to store the photonic quantum state for long periods as it
possesses lower damping than the photonic and magnon modes. Thus our proposed
scheme offers a possibility of using magnomechanical systems as quantum memory
for photonic quantum information.
