Reporter-spin-assisted T₁ relaxometry with nitrogen-vacancy centers in diamond

Detection of fluctuating magnetic fields lends important insight into the dynamics of condensed-matter systems and decoherence processes. The nitrogen-vacancy (NV) center in diamond constitutes a powerful tool for the noninvasive and quantitative measurement of fluctuating fields, with high spatial resolution down to the nm-scale when combined with scanning probe microscopy. To circumvent the difficulties of engineering arbitrarily shallow and charge stable NVs and to achieve higher spatial resolution, we propose utilizing auxiliary relaxation reporter spins on the diamond surface to detect fluctuating magnetic fields at nanoscale. We present quantitative simulations of the sensitivity and spatial resolution enhancements compared to NV T₁ relaxometry. To benchmark our imaging methods, we synthesize Gd³⁺ spin labels patterned via DNA origami structures and present relaxometry images of these structures, pushing towards molecular-scale imaging.