Frequency- and Power-Dependent Optical Response of a Cesium Rydberg Microwave Receiver

We show experimentally obtained frequency- and power-dependent optical response of a room-temperature cesium vapor cell used as a Rydberg microwave receiver based on electromagnetically induced transparency. An applied microwave field couples the 70S1/2 Rydberg state to the nearby 70P1/2, 70P3/2, 69P1/2, and 69P3/2 states, modifying the probe-transmission spectrum. Probe transmission is recorded over an 800 MHz range of coupling laser detunings. These EIT spectra are measured for RF frequencies from 9 to 13.5 GHz and over a 40 dB range of RF power. We analyze the RF induced splittings in the recorded EIT spectra. We observe both limiting cases, where the EIT peak separation is either dominated by the RF detuning or by the RF power. At higher powers we are also able to observe complex features due to coupling of multiple nearby Rydberg states. We further analyze the probe-transmission signal at zero coupling-laser detuning. Sigmoidal fits to the power-response curves are used to determine the midpoint power and the 10–90% transition interval as functions of RF frequency. We observe a nearly uniform transition interval across the measured frequency range away from resonances, while near the degenerate two-photon resonances the interval is larger, yielding a larger dynamic range at the cost of lower responsivity.