Ashley J. Tyler | Searcharxiv

arXiv2026

Quantum Sensing for Spatial Spin Noise Mapping via Nitrogen-Vacancy Magnetic Quenching in Diamond

Detecting and mapping spin noise can reveal spatial variations in surface defect states, catalytic residues, free radicals, and spintronic materials. However, bulk measurements average over spatial heterogeneity, while scanning-probe maps require sequential rastering. Here, we demonstrate a microwave-free magnetic quenching (MQ) method for wide-field spin-noise mapping using nitrogen-vacancy (NV) centres in diamond. The protocol combines continuous LED illumination with a low-frequency, amplitude-modulated magnetic field, avoiding resonant microwave delivery or pulsed optical hardware. Field-induced spin-state mixing reduces NV photoluminescence, providing the primary contrast mechanism. We examine the response as a function of optical power and magnetic modulation amplitude, interpreting the results using a spin-state mixing model. The method is validated with aqueous gadobutrol concentration series, showing trends consistent with optically detected magnetic resonance (ODMR) measurements. We map spin-noise variations across boron nitride and single-walled carbon nanotube samples with differing defect and metallic catalyst contributions, supported by electron microscopy and spectroscopy. Notably, MQ detects a spin-noise response in boron nitride nanotubes that is silent in bulk EPR spectroscopy. This approach provides a practical framework for spatially resolved spin-noise sensing across quantum technologies and advanced functional materials.

physics.app-ph↗

arXiv2024

Determining sensor geometry and gain in a wearable MEG system

Optically pumped magnetometers (OPMs) are compact and lightweight sensors that can measure magnetic fields generated by current flow in neuronal assemblies in the brain. Such sensors enable construction of magnetoencephalography (MEG) instrumentation, with significant advantages over conventional MEG devices including adaptability to head size, enhanced movement tolerance, lower complexity and improved data quality. However, realising the potential of OPMs depends on our ability to perform system calibration, which means finding sensor locations, orientations, and the relationship between the sensor output and magnetic field (termed sensor gain). Such calibration is complex in OPMMEG since, for example, OPM placement can change from subject to subject (unlike in conventional MEG where sensor locations or orientations are fixed). Here, we present two methods for calibration, both based on generating well-characterised magnetic fields across a sensor array. Our first device (the HALO) is a head mounted system that generates dipole like fields from a set of coils. Our second (the matrix coil (MC)) generates fields using coils embedded in the walls of a magnetically shielded room. Our results show that both methods offer an accurate means to calibrate an OPM array (e.g. sensor locations within 2 mm of the ground truth) and that the calibrations produced by the two methods agree strongly with each other. When applied to data from human MEG experiments, both methods offer improved signal to noise ratio after beamforming suggesting that they give calibration parameters closer to the ground truth than factory settings and presumed physical sensor coordinates and orientations. Both techniques are practical and easy to integrate into real world MEG applications. This advances the field significantly closer to the routine use of OPMs for MEG recording.

physics.med-ph↗