Spatially-resolved potential measurement with ion crystals
  We present a method to measure potentials over an extended region using one-dimensional ion crystals in a radio frequency (RF) ion trap. The equilibrium spacings of the ions within the crystal allow the determination of the external forces acting at each point. From this the overall potential, and also potentials due to specific trap features, are calculated. The method can be used to probe potentials near proximal objects in real time, and can be generalized to higher dimensions. 
Michael Brownnutt, Maximilian Harlander, Wolfgang H\"ansel, Rainer   Blatt
quant-ph