Design of Varactor Diode-Based Frequency-Tunable Electric Field Local Enhancement Resonator for Quantum Microwave Measurements

The quantum microwave measurement technique based on Rydberg atoms enables the measurement of microwave electric field over an ultrawide frequency range. To improve the sensitivity while maintaining its broadband characteristics, we propose a tunable local electric field enhancement resonator loaded with varactor diodes. Simulation results show that the tunable frequency covers from 305 MHz to 455 MHz and the electric field enhancement multiplier is higher than 40 dB. Experimental test results based on the AC Stark effect demonstrate that the resonator has the electric field enhancement capability from 323 MHz to 443 MHz by changing the bias voltage of the varactor diode. This tunable electric field enhancement resonator is expected to improve the ability of quantum microwave technology in broadband measurements.