Probing bandwidth and sensitivity in Rydberg atom sensing via optical homodyne and rf heterodyne detection

Rydberg atom based sensors allow for SI traceable measurements and show promise for applications in the field of communication and radar technologies. In this article, we investigate the bandwidth and sensitivity of a Rydberg atom-based sensor in a rubidium vapor cell using Rydberg electromagnetically induced transparency (EIT) spectroscopy. We employ a radio-frequency (RF) heterodyne measurement technique in combination with an optical homodyne setup to extend the achievable range between sensitivity and bandwidth in a Rydberg sensor. While the bandwidth of Rydberg sensors are limited by the transit time of atoms and the Rabi frequency of the coupling field, achieving higher bandwidth through smaller beam sizes is thought to compromise sensitivity due to reduced EIT signal strength. Using optical homodyne detection, we demonstrate that sensitivity is preserved while achieving a response bandwidth of 8 MHz. In addition, using the Rydberg sensor, we receive digital communication signals and present error vector magnitude (EVM) measurements as a function of varying symbol rates and bandwidth of the Rydberg sensor. Furthermore, the sensor's performance is compared with a conventional RF mixer. We establish that the bandwidth of a Rydberg sensor when receiving a pure tone is not the same as the bandwidth of the sensor when receiving a modulated signal. This difference results from the spreading of symbols in the frequency domain, leading to a reduction of the signal to noise ratio (SNR) and an accumulation of noise over the total span of the modulated signal.