Enhancement of optomagnonic coupling and microwave-optical conversion via magnetic anisotropy

Efficient microwave-optical frequency conversion is critical for building long-distance quantum networks. Magnons in ferromagnets offer a promising mediator for this conversion, owing to their ability to couple to both microwave and optical fields. However, the magnon-mediated microwave-optical conversion efficiency is severely limited by the inherently weak optomagnonic coupling. Here, we propose a scheme to enhance the optomagnonic coupling by utilizing the intrinsic magnetic anisotropy in a yttrium iron garnet (YIG) thin film. The presence of magnetic anisotropy establishes a squeezed vacuum for the magnonic ground state, which enhances the effective optomagnonic coupling strength by a factor of $\cosh (r)$, where r is the squeezing parameter. This results in a significant boost of the corresponding cooperativities and, consequently, the microwave-to-optical conversion efficiency by several orders of magnitude for large squeezing. Our approach harnesses magnon squeezing as an intrinsic resource to strengthen optomagnonic interactions, creating opportunities for high-efficiency microwave-optical conversion.