Realizing $Q$ > 300,000 in diamond microdisks for optomechanics via etch optimization

TL;DR

This paper presents an optimized etching process for diamond microdisks that significantly increases the optical quality factor to over 300,000, enabling advanced optomechanics experiments.

Contribution

The authors develop a new etching technique that enhances the optical quality factor of diamond microdisks by four times, reaching $Q$ > 300,000, suitable for quantum optomechanics.

Findings

Achieved $Q$ ~ 335,000 in diamond microdisks.

Surface imperfections limit the $Q$ despite optimization.

Modified pedestal geometry may reduce mechanical dissipation.

Abstract

Nanophotonic structures in single--crystal diamond (SCD) that simultaneously confine and co-localize photons and phonons are highly desirable for applications in quantum information science and optomechanics. Here we describe an optimized process for etching SCD microdisk structures designed for optomechanics applications. This process allows the optical quality factor, $Q$, of these devices to be enhanced by a factor of 4 over previous demonstrations to $Q \sim 335,000$, which is sufficient to enable sideband resolved coherent cavity optomechanical experiments. Through analysis of optical loss and backscattering rates we find that $Q$ remains limited by surface imperfections. We also describe a technique for altering microdisk pedestal geometry which could enable reductions in mechanical dissipation.