PCB-Based Electrically Tunable Resonator for VHF Band Rydberg Atomic Enhancement Sensing

Highly sensitive detection of very high frequency (VHF) band fields poses a challenge for Rydberg atomic sensing since resonant detection requires exciting atoms to extremely high energy states. We demonstrate a PCB-based electrically tunable resonator (PETR) for enhancing the sensing sensitivity of the Rydberg atomic sensor to VHF band fields. In this approach, the sub-wavelength PETR is made of PCB, which offers improved mechanical strength and miniaturization. During the measurements, a parallel-plate waveguide (PPWG) is utilized as the radio frequency (RF) field launcher to eliminate unintentional scattering from the surroundings. By adjusting the bias voltage applied to the tuning varactor of the PETR, we can continuously tune the resonant frequencies from 187 to 293.6 MHz, corresponding to a relative bandwidth of 44%. There is a fluctuation in the enhancement factor of the PETR, ranging from 17.6 to 60.1, which is primarily caused by misalignment between the laser beam and the resonant area. Furthermore, employing the off-resonant Rydberg atomic heterodyne technique, we investigated the sensitivity of the system. In the absence of the PETR, the sensitivity for an RF signal at 250.5 MHz was found to be
$97.44 ~\mu \text{V}$
/cm
$\sqrt {\text {Hz}}$
. However, with the presence of our PETR, the sensitivity significantly improved to
$1.73 ~\mu \text{V}$
/cm
$\sqrt {\text {Hz}}$
, indicating a remarkable enhancement capacity of 56.23 times or 35 dB. This enhancement resonator holds great potential for improving Rydberg atomic sensing, particularly in the VHF band.