  We investigate a hybrid quantum system where an ensemble of nitrogen-vacancy
(NV) centers in diamond is interfaced with a piezomagnetic superlattice that
supports surface phonon polaritons (SPhPs). We show that the strong magnetic
coupling between the collective spin waves in the NV spin ensemble and the
quantized SPhPs can be realized, thanks to the subwavelength nature of the
SPhPs and relatively long spin coherence times. The magnon-polariton coupling
allows different modes of the SPhPs to be mapped and orthogonally stored in
different spatial modes of excitation in the solid medium. Because of its easy
implementation and high tunability, the proposed hybrid structure with NV spins
and piezoactive superlattices could be used for quantum memory and quantum
computation.
