  Strong long-distance spin-magnon coupling is essential for solid-state
quantum information processing and single qubit manipulation. Here, we propose
an approach to realize strong spin-magnon coupling in a hybrid optomechanical
cavity-spin-magnon system, where the optomechanical system, consisting of two
cavities coupled to a common high-frequency mechanical resonator, acts as
quantum interface. By eliminating the mechanical mode, a position-position
coupling and two-mode squeezing of two cavities are induced. In the squeezing
presentation, the spin-photon, magnon-photon and photon-photon coupling
strengths are exponentially amplified, thus lower- and upper-branch polaritons
(LBP and UBP) are generated by strongly coupled squeezed modes of two cavities.
Utilizing the critical property of the LBP, the coupling between the spin qubit
(magnon) and LBP is greatly enhanced, while the coupling between the spin qubit
(magnon) and UBP is fully suppressed. In the dispersive regime, strong and
tunable spin-magnon coupling is induced by the virtual LBP, allowing quantum
state exchange between them. Our proposal provides a promising platform to
construct magnon-based hybrid systems and realize solid-state quantum
information processing with optomechanical interfaces.
