Fundamental Sensitivities of Electrically Small Antennas and Rydberg Quantum Receivers.

Rydberg Sensors hold promise for highly sensitive RF measurements in the high frequency (HF) band of 3 –30 MHz and are of interest for a multitude of reasons including their ability to make non-perturbing measurements and their compact size. In the HF band, their mm to cm scale sensor heads are significantly smaller than traditional impedance matched antennas. We evaluate the fundamental sensitivities of electrically small loop and dipole antennas coupled to unmatched loads and quantum Rydberg-atom sensors in the HF regime. Although Rydberg sensors are fundamentally 10 dB more sensitive than unmatched electrically small dipoles, with currently available techniques, Rydberg sensors are approximately 50 dB less sensitive than classical antennas. Our results indicate there is room for growth within the field and more research is needed to advance Rydberg sensors towards their fundamental limits.