Quantum Limited Spatial Resolution of NV-Diamond Magnetometry

TL;DR

This paper introduces a novel optical mode demultiplexing protocol that significantly improves the spatial resolution and brightness estimation of NV-diamond magnetometry beyond the diffraction limit, enhancing atomic-scale sensing capabilities.

Contribution

The work develops a two-stage sensing protocol using spatial mode demultiplexing to enhance localization and brightness estimation accuracy in NV-diamond magnetometry.

Findings

Localization accuracy improved by 6 times

Brightness estimation accuracy doubled

Performance surpasses conventional imaging methods

Abstract

Optically addressable ensembles of solid-state defects, such as nitrogen vacancy (NV) centers, are a leading modality for imaging-based magnetometry, thermometry and strain sensing. However, monitoring the fluorescence of individual defects within a sub-diffraction ensemble remains an outstanding challenge that currently limits access to atomic-scale features and dynamics. For compact clusters of NVs, imaging-based atomic sensing may be formulated as a low-dimensional multiparameter estimation task in which one seeks to localize each defect and quantify the field strength in its immediate vicinity. In this work, we employ optical spatial mode demultiplexing (SPADE) to enhance localization and brightness estimation accuracy at sub-diffraction scales. Specifically, we develop a two-stage sensing protocol that augments direct imaging by projecting the incoming optical field onto point spread function (PSF)-adapted spatial modes and Yuen-Kennedy-Lax (YKL) spatial modes, enabling efficient extraction of emitter positions and brightnesses. We numerically evaluate the statistical performance of our protocol for sub-diffraction optically detected magnetic resonance (ODMR) and Rabi sensing experiments. Compared to conventional focal plane intensity measurements, our protocol improves emitter localization accuracy by $6\times$ and brightness estimation accuracy by $2\times$ for tightly confined ensembles, residing well below the diffraction limit.