# Determination of Intrinsic Effective Fields and Microwave Polarizations by High-Resolution Spectroscopy of Single NV Center Spins

## TL;DR

This study uses high-resolution spectroscopy to analyze the intrinsic effective fields affecting single NV center spins in diamond, revealing strain as the dominant factor and introducing a method for microwave polarization analysis relevant for quantum sensing.

## Contribution

It provides a detailed model and experimental method to determine the strength and direction of intrinsic fields and microwave polarization at the single-spin level.

## Key findings

- Strain dominates the intrinsic effective field in the studied diamond.
- A new method for microwave polarization analysis is demonstrated.
- Insights into low-field quantum sensing applications are provided.

## Abstract

We present high-resolution optically detected magnetic resonance (ODMR) spectroscopy on single nitrogen-vacancy (NV) center spins in diamond at and around zero magnetic field. The experimentally observed transitions depend sensitively on the interplay between the microwave (MW) probing field and the local intrinsic effective field comprising strain and electric fields, which act on the NV spin. Based on a theoretical model of the magnetic dipole transitions and the MW driving field, we extract both the strength and the direction of the transverse component of the effective field. Our results reveal that for the diamond crystal under study, strain is the dominant contribution to the effective field. Our experiments further yield a method for MW polarization analysis in a tunable, linear basis, which we demonstrate on a single NV spin. Our results are of importance to low-field quantum sensing applications using NV spins and form a relevant addition to the ever-growing toolset of spin-based quantum sensing.