Sub-Wavelength Imaging and Field Mapping via EIT and Autler-Townes   Splitting In Rydberg Atoms
  We present a technique for measuring radio-frequency (RF) electric field strengths with sub-wavelength resolution. We use Rydberg states of rubidium atoms to probe the RF field. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect, and we detect the splitting via electromagnetically induced transparency (EIT). We use this technique to measure the electric field distribution inside a glass cylinder with applied RF fields at 17.04 GHz and 104.77 GHz. We achieve a spatial resolution of $\bf{\approx}$100 $\bf{\mu}$m, limited by the widths of the laser beams utilized for the EIT spectroscopy. We numerically simulate the fields in the glass cylinder and find good agreement with the measured fields. Our results suggest that this technique could be applied to image fields on a small spatial scale over a large range of frequencies, up into the sub-THz regime. 
Christopher L. Holloway, Joshua A. Gordon, Andrew Schwarzkopf, David   A. Anderson, Stephanie A. Miller, Nithiwadee Thaichar...
physics.atom-ph