  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.
