Sensitivity Comparison of Rydberg Atom-Based Radio-Frequency Electric Field Detection: Ionization Current Versus Optical Readout

We investigate a technique for detecting radio-frequency (RF) electric fields in a Cesium (Cs) vapor cell at room temperature by collecting charge from ionized Rydberg atoms and compare its performance with the established method of electromagnetically induced transparency (EIT). By applying a known RF field, we measure the response from both the electrical (ionization current-based) and optical (EIT-based) readouts. The ionization current-based method yields a sensitivity of 22~$\mu$Vm$^{-1}$Hz$^{-1/2}$, while the EIT-based method achieves 3.7~$\mu$Vm$^{-1}$Hz$^{-1/2}$. The sensitivity of the ionization current-based method is limited by thermal noise arising from a 2.2~k$\Omega$ resistance between the collection electrodes, attributed to a thin Cs film on the inner surfaces of the vapor cell. Controlling or eliminating the Cs layer can significantly improve the sensitivity of this ionization approach.