  Hybrid quantum systems involving solid-state spins and superconducting
microwave cavities play a crucial role in quantum science and technology, but
improving the spin-photon coupling at the single quantum level remains
challenging in such systems. Here, we propose a simple technique to strongly
couple a single solid-state spin to the microwave photons in a superconducting
coplanar waveguide (CPW) cavity via a magnetic microsphere. We show that,
strong coupling at the single spin level can be realized by virtual magnonic
excitations of a nearby micromagnet. The spin-photon coupling strength can be
enhanced up to typically four orders of magnitude larger than that without the
use of the micromagnet. This work can find applications in quantum information
processing with strongly coupled solid-state spin-photonic systems.
