Superresolution optical magnetic imaging and spectroscopy using   individual electronic spins in diamond
  Nitrogen vacancy (NV) color centers in diamond are a leading modality for both superresolution optical imaging and nanoscale magnetic field sensing. In this work, we solve the remaining key challenge of performing optical magnetic imaging and spectroscopy selectively on multiple NV centers that are located within a diffraction-limited field-of-view. We use spin-RESOLFT microscopy to enable precision nanoscale mapping of magnetic field patterns with resolution down to ~20 nm, while employing a low power optical depletion beam. Moreover, we use a shallow NV to demonstrate the detection of proton nuclear magnetic resonance (NMR) signals exterior to the diamond, with 50 nm lateral imaging resolution and without degrading the proton NMR linewidth. 
Jean-Christophe Jaskula, Erik Bauch, Silvia Arroyo-Camejo, Mikhail D.   Lukin, Stefan W. Hell, Alexei S. Trifonov, Ronald L....
quant-ph cond-mat.mes-hall