# Frequency Locking Method for Frequency Standards Based on Diamond NV Centers

## TL;DR

This paper introduces a new method for stabilizing microwave frequencies using diamond NV centers, which is less affected by magnetic field changes.

## Contribution

A novel frequency locking method using the central peak of ODMR spectra, improving stability in diamond-based quantum frequency standards.

## Key findings

- The central-peak locking method achieves a short-term frequency stability of 1.73 × 10−7 at 200 s.
- Central-peak locking significantly reduces frequency drift under varying magnetic fields compared to side-peak methods.

## Abstract

In this study, frequency locking technology is investigated for high-stability microwave frequency standards based on diamond nitrogen-vacancy (NV) centers. Conventional locking methods typically utilize the side peaks induced via Zeeman splitting; however, this approach renders the frequency output highly susceptible to ambient magnetic field fluctuations. To address this limitation, a robust frequency locking method based on the central peak of the Optically Detected Magnetic Resonance (ODMR) spectrum is proposed. By systematically optimizing the bias magnetic field, the proposed method exploits the central peak’s inherent insensitivity to magnetic field variations and its narrower linewidth in environments with weak magnetic fields, thereby enhancing the quality factor of the frequency discrimination curve. The experimental results demonstrate that the proposed scheme achieves closed-loop locking of the 2.87 GHz microwave frequency, reaching short-term frequency stability (Allan deviation) of 1.73 × 10−7 at 200 s. Comparative tests under gradient magnetic fields further confirm that central-peak locking significantly suppresses frequency drift compared to side-peak methods. This study provides a vital technical pathway for the development of miniaturized, interference-resistant solid-state quantum frequency standards.