  We investigate the sensitivity of three-photon EIT in Rydberg atoms to radio
frequency detection and compare it against conventional two-photon systems.
Specifically, we model the 4-level and 5-level atomic system and compare how
the transmission of the probe changes with different powers of the lasers used
and strengths of the RF field. In this model, we also define a sensitivity
metric to best relate to the operation of the current best experimental
implementation based on shot noise limited detection. We find that the
three-photon system boasts much narrower line widths compared to the
conventional two-photon EIT. However, these narrow line features do not align
with the regions of the best sensitivity. In addition to this, we calculate the
expected sensitivity for the two-photon Rydberg sensor and find that the best
achievable sensitivity is over an order of magnitude better than the current
measured values of 5 uV/m/Hz. However, by accounting for the additional noise
sources in the experiment and the quantum efficiency of the photo-detectors,
the values are in good agreement.
