Shortwave Ultrahigh-Sensitivity Rydberg Atomic Electric Field Sensing Based on a Subminiature Resonator

Rydberg atomic electric field sensors have attracted the attention of international researchers due to their powerful electric field measurement capabilities. Especially in the shortwave (SW) frequency band (3–30 MHz), using only millimeter-level sensors to receive SW signals is undoubtedly attractive. However, due to the extremely difficult excitation of the Rydberg atoms that resonate with the SW frequency, the sensitivity of the Rydberg atoms SW measurement is low. Here, we report that a method to improve the SW sensitivity by using an SW resonator, which is extremely small in electrical size ( $0.0043\lambda \times 0.0035\lambda \times 0.007\lambda $ ), can achieve continuous resonant frequency coverage from 9.365 to 10.223 MHz and can increase the sensitivity of electric field measurement by a factor of 8633. In the state of far off-resonant, we have achieved a detectable field strength as low as $2.41~\mu $ V/m with a sensitivity of $1.71~\mu $ V/mHz $^{1/2}$ using the heterodyne Rydberg atom-based mixer method, which realizes ultrahigh-sensitivity measurement of SWs. In addition, for the first time outside the laboratory, we directly received an amplitude-modulated broadcast signal with 880 km (the straight-line distance between Changsha and Baoji) at 9.81 MHz in the form of a subminiature resonator combined with a Rydberg field probe (RFP), which verified the powerful ability of this sensing scheme.