Photonic crystal cavities based on suspended yttrium iron garnet nanobeams

Abstract

We report the fabrication and optical characterization of an air-suspended photonic crystal nanobeam cavity in yttrium-iron-garnet (YIG) realized by focused-ion-beam milling. YIG's combination of low optical loss and ferrimagnetism makes it highly attractive for quantum technologies, yet prior work has largely been focused on millimeter-scale spheres and simple microstructures, hindering true on-chip integration. Demonstrating nanometer-scale patterning in a suspended geometry therefore represents an important advance. Finite-element simulations predict that the same structure supports a flapping-type mechanical mode at $\Omega / 2\pi \approx 1.52 \,\text{GHz}$ and a backward-volume spin-wave mode at $\Omega / 2\pi = 11.59 \,\text{GHz}$ under an in-plane bias field. Although we measure only the photonic resonance (intrinsic $Q \sim 2 \times 10^{3}$) in this study, the device lays the groundwork for future exploration of coupled photon-phonon-magnon dynamics once higher optical quality factors are achieved.