Wide-Field Dynamic Magnetic Microscopy Using Double-Double Quantum Driving of a Diamond Defect Ensemble

Wide-field magnetometry can be realized by imaging the optically detected magnetic resonance of diamond nitrogen-vacancy ($\mathrm{N}$-$V$) center ensembles. However, $\mathrm{N}$-$V$ ensemble inhomogeneities significantly limit the magnetic field sensitivity of these measurements. We demonstrate a double-double quantum (DDQ) driving technique to facilitate wide-field magnetic imaging of dynamic magnetic fields at a micron scale. DDQ imaging employs four-tone radio-frequency pulses to suppress inhomogeneity-induced variations of the $\mathrm{N}$-$V$ resonance response. As a proof of principle, we use the DDQ technique to image the dc magnetic field produced by individual magnetic nanoparticles tethered by single DNA molecules to a diamond-sensor surface. This demonstrates the efficacy of the diamond $\mathrm{N}$-$V$ ensemble system in high-frame-rate magnetic microscopy, as well as single-molecule biophysics applications.