Sub-wavelength microwave electric field imaging using Rydberg atoms   inside atomic vapor cells
  We have recently shown that Alkali atoms contained in a vapor cell can serve as a highly accurate standard for microwave electric field strength as well as polarization using the principles of Rydberg atom electromagnetically induced transparency. Here, we show, for the first time, that Rydberg atom electromagnetically induced transparency can be used to image microwave electric fields with unprecedented precision. The spatial resolution of the method is far into the sub-wavelength regime. The electric field resolutions are similar to those we have demonstrated in our prior experiments. Our experimental results agree with finite element calculations of test electric field patterns. 
H.Q. Fan, S. Kumar, R. Daschner, H. K\"ubler, and J. P. Shaffer
physics.atom-ph physics.optics quant-ph