Fabrication of Sawfish photonic crystal cavities in bulk diamond

TL;DR

This paper presents a fabrication process for Sawfish photonic crystal cavities in diamond, achieving high quality factors and robust design, to enhance photon emission and coupling for quantum photonic applications.

Contribution

It introduces a practical fabrication method for Sawfish cavities in diamond with high Q-factors and demonstrates their robustness against fabrication imperfections.

Findings

Achieved Q-factors up to 3825.

Cavity resonances deviate less than 1.2% from simulations.

Enhanced emission rate by a factor of 46.

Abstract

Color centers in diamond 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 enhance the emission rate by a factor of 46 and couple photons into a single-mode fiber with an efficiency of 88%. The presented process allows for the fabrication of fully suspended devices with a total length of 20.5 $\mu$m and features size 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 3825. 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 0.9 (1.2)% from the corresponding simulated values. This proves that the Sawfish design is robust against fabrication imperfections, which makes it an attractive choice for the development of quantum photonic networks.