  In this paper we demonstrate the detection of millimeter waves via
Autler-Townes splitting in 85Rb Rydberg atoms. This method may provide an
independent, atom-based, SI-traceable method for measuring mm-wave electric
fields, which addresses a gap in current calibration techniques in the mm-wave
regime. The electric- field amplitude within a rubidium vapor cell in the WR-10
waveguide band is measured for frequencies of 93 GHz, and 104 GHz. Relevant
aspects of Autler-Townes splitting originating from a four-level
electromagnetically induced transparency scheme are discussed. We measure the
E-field generated by an open-ended waveguide using this technique. Experimental
results are compared to a full-wave finite element simulation.
