To isolate the Autler-Townes splitting induced by a single selected THz transition in a Cs Rydberg atom, a Zeeman-resolved EIT (electromagnetically induced transparency) signal was obtained in a high magnetic field. The electronic state was controlled by the polarizations of two lasers exciting the Cs atoms and the chosen magnetic quantization axis. Applying a THz wave with controlled polarization then enabled an observation of the Autler-Townes splitting induced by its coupling to a single dipole transition.
We report on rubidium vapor-cell Rydberg electromagnetically induced transparency (EIT) in a 0.7~T magnetic field where all involved levels are in the hyperfine Paschen-Back regime, and the Rydberg state exhibits a strong diamagnetic interaction with the magnetic field. Signals from both
85Rb and
87Rb are present in the EIT spectra. This feature of isotope-mixed Rb cells allows us to measure the field strength to within a
±0.12\% relative uncertainty. The measured spectra are in excellent agreement with the results of a Monte Carlo calculation and indicate unexpectedly large Rydberg-level dephasing rates. Line shifts and broadenings due to small inhomogeneities of the magnetic field are included in the model.