Quantum sensing with nitrogen-vacancy centers in diamond: from correlated magnetometry to novel spin dynamics in 2D magnets

Speaker: Xuan Hoang Le

Affiliation: Harvard University

Abstract: The magnetic dynamic structure factor and its Fourier conjugate, the two-point spatio-temporal spin correlation function, fundamentally characterize the magnetic orders and properties of materials. Established scattering-based techniques to probe this quantity often require spatially averaging across a macroscopic sample volume, thus incompatible with atomically thin samples.
In the first part (1), we demonstrate locally measuring correlations of wideband magnetic signals with sub diffraction resolution and sensitivity compatible with two-dimensional samples. Our technique employs two nitrogen-vacancy (NV) centers in diamond as nanoscale magnetometers, spectrally resolved by inhomogeneous optical transitions. Using high-fidelity optical readout and long spin coherence time, we probe correlated MHz-range noise with sensitivity of 15 nT Hz−1/4. In addition, we use this system for correlated T1 relaxometry, enabling correlation measurements of GHz-range noise. Under such externally applied noise, while individual NV centers exhibit featureless relaxation, their correlation displays rich coherent and incoherent dynamics reminiscent of superradiance physics. This capability to probe high frequency correlations provides a powerful tool for investigating various condensed-matter phenomena characterized by nonlocal correlations.
In the second part (2), we leverage various NV-based quantum sensing protocols for noise spectroscopy of criticality and spin dynamics in the van der Waals magnet Cr2Ge2Te6. Ensemble-averaged measurements reveal strong critical fluctuations and slowing down near the ferromagnetic phase transition. Furthermore, in the ferromagnetic phase, we observe evidence of low-frequency coherent spin dynamics that arise from motions of skyrmionic bubbles. We expect spatio-temporal correlation measurements to shed light on the characteristic lengthscales and effect of dimensionality on these critical and skyrmionic dynamics.

(1) X. H. Le et al. “Wideband covariance magnetometry below the diffraction limit.” Phys. Rev. Lett.
135 (17), 170803 (2025).

(2) X. H. Le et al. “Critical and skyrmionic dynamics in a two-dimensional magnet probed by quantum
sensors”, in prep (2026).