Nanoscale covariance magnetometry with diamond quantum sensors

TL;DR

This paper introduces a novel nanoscale magnetometry technique using diamond NV centers that measures correlations between multiple sensors simultaneously, revealing spatiotemporal magnetic field structures.

Contribution

It proposes and demonstrates a new sensing modality that captures correlations between NV centers, surpassing traditional averaging methods and enabling detailed noise and dynamics analysis.

Findings

Successfully measured correlated noise using spin-to-charge readout.

Developed a spectral reconstruction protocol for local and nonlocal noise sources.

Showed that optimizing readout noise is essential for correlation measurements.

Abstract

Nitrogen vacancy (NV) centers in diamond are atom-scale defects with long spin coherence times that can be used to sense magnetic fields with high sensitivity and spatial resolution. Typically, the magnetic field projection at a single point is measured by averaging many sequential measurements with a single NV center, or the magnetic field distribution is reconstructed by taking a spatial average over an ensemble of many NV centers. In averaging over many single-NV center experiments, both techniques discard information. Here we propose and implement a new sensing modality, whereby two or more NV centers are measured simultaneously, and we extract temporal and spatial correlations in their signals that would otherwise be inaccessible. We analytically derive the measurable two-point correlator in the presence of environmental noise, quantum projection noise, and readout noise. We show that optimizing the readout noise is critical for measuring correlations, and we experimentally demonstrate measurements of correlated applied noise using spin-to-charge readout of two NV centers. We also implement a spectral reconstruction protocol for disentangling local and nonlocal noise sources, and demonstrate that independent control of two NV centers can be used to measure the temporal structure of correlations. Our covariance magnetometry scheme has numerous applications in studying spatiotemporal structure factors and dynamics, and opens a new frontier in nanoscale sensing.