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, current is passed through wires placed on the diamond chip surface, and the resulting magnetic field patterns are imaged with sub- micron resolution over a 140 $\rm{\mu m}$ $\times$ 140 $\rm{\mu m}$ field of view, giving single-pixel sensitivity $\sim 100$ $\rm{nT/\sqrt{Hz}}$. We discuss ongoing efforts to further improve sensitivity, such as using dynamical decoupling techniques in order to extend coherence times.