# Diamond Phononic Crystal Spin-Mechanical Resonators with Spectrally Stable Nitrogen Vacancy Centers

## TL;DR

This paper presents the design and fabrication of diamond spin-mechanical resonators embedded in a 2D phononic crystal lattice, achieving spectrally stable nitrogen vacancy centers with narrow optical linewidths.

## Contribution

It introduces a membrane-in-bulk fabrication approach and graded soft oxygen etching to improve NV center stability in 2D diamond resonators.

## Key findings

- Resonators exhibit GHz in-plane compression modes within a phononic band gap.
- Optical linewidth of NV centers reduced to as narrow as 330 MHz.
- The fabrication method overcomes limitations of previous approaches.

## Abstract

We report the design and fabrication of diamond spin-mechanical resonators embedded in a two-dimensional (2D) phononic crystal square lattice. The rectangular resonator features GHz in-plane compression modes protected by the phononic band gap of the square lattice. A membrane-in-bulk approach is developed for the fabrication of the suspended 2D structure. This approach overcomes the limitations of the existing approaches, which are either incompatible with the necessary high-temperature thermal annealing or unsuitable for 2D structures with the required feature size. Graded soft oxygen etching, with the etching rate decreased gradually to below 1 nm/minute, is used to remove defective surface layers damaged by reactive ion etching. Combining the graded etching with other established surface treatment techniques reduces the optical linewidth of nitrogen vacancy centers in resonators with a thickness below 1 micron to as narrow as 330 MHz.

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Source: https://tomesphere.com/paper/1905.01251