  Quantum computing, quantum communication and quantum networks rely on hybrid
quantum systems operating in different frequency ranges. For instance, the
superconducting qubits work in the gigahertz range, while the optical photons
used in communication are in the range of hundreds of terahertz. Due to the
large frequency mismatch, achieving the direct coupling and information
exchange between different information carriers is generally difficult.
Accordingly, a quantum interface is demanded, which serves as a bridge to
establish information linkage between different quantum systems operating at
distinct frequencies. Recently, the magnon mode in ferromagnetic spin systems
has received significant attention. While the inherent weak optomagnonic
coupling strength restricts the microwave-to-optical photon conversion
efficiency using magnons, the versatility of the magnon modes, together with
their readily achievable strong coupling with other quantum systems, endow them
with many distinct advantages. Here, we realize the magnon-based
microwave-light interface by adopting an optical cavity with adjustable free
spectrum range and different kinds of magnetostatic modes in two microwave
cavity configurations. By optimizing the parameters, an internal conversion
efficiency of $1.28 \times 10^{-7}$ is achieved. We analyze the impact of
various parameters on the microwave-to-optics conversion. The study provides
useful guidance and insights to further enhancing the microwave-to-optics
conversion efficiency using magnons.
