Design and fabrication of robust hybrid photonic crystal cavities.

Heterogeneously integrated hybrid photonic crystal cavities enable strong light-matter interactions with solid state, optically addressable quantum memories. A key challenge to realizing high quality factor () hybrid photonic crystals is the reduced index contrast on the substrate compared to suspended devices in air. This challenge is particularly acute for color centers in diamond because of diamond's high refractive index, which leads to increased scattering loss into the substrate. Here, we develop a design methodology for hybrid photonic crystals utilizing a detailed understanding of substrate-mediated loss, which incorporates sensitivity to fabrication errors as a critical parameter. Using this methodology, we design robust, high-Q, GaAs-on-diamond photonic crystal cavities, and by optimizing our fabrication procedure, we experimentally realize cavities with approaching 30,000 at a resonance wavelength of 955 nm.