Fabrication of Sawfish photonic crystal cavities in bulk diamond

Abstract

Color centers in diamonds are quantum systems with optically active spin-states that show long coherence times and are, therefore, a promising candidate for the development of efficient spin–photon interfaces. However, only a small portion of the emitted photons is generated by the coherent optical transition of the zero-phonon line (ZPL), which limits the overall performance of the system. Embedding these emitters in photonic crystal cavities improves the coupling to the ZPL photons and increases their emission rate. Here, we demonstrate the fabrication process of “Sawfish” cavities, a design recently proposed that has the experimentally realistic potential to simultaneously provide a high waveguide coupling efficiency and significantly enhance the emission rate. The presented process allows for the fabrication of fully suspended devices with a total length of 20.5 μm and feature sizes as small as 40 nm. The optical characterization shows fundamental mode resonances that follow the behavior expected from the corresponding design parameters and quality (Q) factors as high as (3800 ± 1200). Finally, we investigate the effects of nanofabrication on the devices and show that, despite a noticeable erosion of the fine features, the measured cavity resonances deviate by only 0.8 (1.2)% from the values estimated by simple inspection via scanning electron microscopy. This proves that the Sawfish design is robust against fabrication imperfections, which makes it an attractive choice for the development of quantum photonic networks.