From atom-based RF metrology to quantum RF receivers and emitters

Recent research in Rydberg atom-based RF metrology and RF receivers is briefly summarized. Main focus of the paper is on a novel Rydberg atom-based emitter which holds significant promise across various applications. Quantum emitters offer well-known advantages, including a high degree of coherence, superradiance, and single photon sources. A particularly intriguing possibility is a low-frequency Rydberg atom-based emitter, which could overcome the Chu-Harrington limit on the Q-factor of electrically small RF antennas. A compact very low frequency (VLF) quantum emitter could have diverse applications ranging from establishing RF links between submerged submarines and air platforms to sounding the ionosphere and magnetosphere from space platforms. Additionally, it could play a role in controlling the population of relativistic electrons in radiation belts, ensuring the safety of space assets during space weather events. Naturally occurring in space, low-frequency Rydberg atom-based emitters manifest themselves through phenomena like radio recombination lines (RRL) and astrophysical masers.