Improving the Sensitivity and Bandwidth of a Rydberg Receiver using Optical Homodyne Detection

Rydberg atom-based electric field sensors are setting new benchmarks compared to conventional antennas in sensing applications. In this work, we investigate the bandwidth and sensitivity of Rydberg atom sensors in a room-temperature rubidium vapor cell using Rydberg electromagnetically induced transparency (EIT) spectroscopy. We employ the measurement technique of radio frequency (RF) superheterodyne along with optical homodyne to overcome the trade-off between sensitivity and the bandwidth of a Rydberg sensor. While the bandwidth of Rydberg sensors is limited by the transit time of atoms and the Rabi frequency of the coupling field, achieving higher bandwidth through smaller beam sizes is generally thought to compromise sensitivity due to a reduction in EIT signal strength. However, by utilizing optical homodyne detection, we demonstrate thatsensitivity is preserved regardless of beam size while achieving a response bandwidth of 10 MHz.

Additionally, we study the effects of the probe and coupling laser beam sizes, as well as the temperature, on the sensitivity and bandwidth of the Rydberg receiver. We show that the sensitivity of the Rydberg sensor is not strictly tied to the interaction volume. Furthermore, we find that the total signal-to-noise ratio (SNR) is not affected by beam size but rather by the Rabi frequency of the coupling field. Improved bandwidth with higher sensitivity in Rydberg receivers has promising application towards communication and radar technologies.