Magnetic field imaging with NV ensembles
  We demonstrate a method of imaging spatially varying magnetic fields using a thin layer of nitrogen-vacancy (NV) centers at the surface of a diamond chip. Fluorescence emitted by the two-dimensional NV ensemble is detected by a CCD array, from which a vector magnetic field pattern is reconstructed. As a demonstration, AC current is passed through wires placed on the diamond chip surface, and the resulting AC magnetic field patterns are imaged using an echo-based technique with sub-micron resolution over a 140 \mu m x 140 \mu m field of view, giving single-pixel sensitivity ~100 nT/\sqrt{Hz}. We discuss ongoing efforts to further improve sensitivity and potential bioimaging applications such as real-time imaging of activity in functional, cultured networks of neurons. 
L. M. Pham, D. Le Sage, P. L. Stanwix, T. K. Yeung, D. Glenn, A.   Trifonov, P. Cappellaro, P. R. Hemmer, M. D. Lukin, H. Pa...
cond-mat.mes-hall quant-ph