High-Q Nanophotonic Resonators on Diamond Membranes using Atomic Layer Deposition TiO₂

Nanophotonic resonators are critical elements in solid-state quantum networks, as they can enable coherent light-matter interactions and enhance zero-photon line emission. In diamond, current techniques to fabricate these devices often introduce significant surface roughness, lattice strain, and poorly controlled surface states which limit device performance and scalability. Here, using atomic layer deposition of TiO₂, we developed a nanophotonic fabrication platform that avoids substrate and sidewall etching while retaining the potential for high-cooperativity interfacing with color centers in thin diamond membranes. The resulting devices are exceptionally smooth and can be built on arbitrary substrates. In this work, we fabricated ring resonators and 1D photonic crystal cavities (PhCCs) with quality factors exceeding 10^4 and integrated high-Q PhCCs with diamond membranes.