A Quantum-Based Microwave Attenuation Standard: Direct Comparison Between Rabi Attenuation and the National Standard

Microwave (MW) quantum sensors have attracted attention due to their promising applications in precision measurements and standards. Recently, we demonstrated the measurement of Rabi attenuation—a quantum-based MW attenuation—using cesium atomic vapor. Rabi attenuation offers several potential advantages over conventional standards; however, the previous study encountered issues with nonlinearity. In this study, we improved the linearity of Rabi attenuation by reducing detuning as one of the nonlinearity factors. We combined the precise determination of resonant frequency using the first-order term of Rabi resonance with the accurate measurement of the MW field using the second-order term. Furthermore, we conducted a direct comparison of Rabi attenuation with the national standard in the National Metrology Institute of Japan (NMIJ) for the first time, allowing for a quantitative evaluation of Rabi attenuation’s linearity. The Rabi attenuation was consistent with the national standard within a range of 33 dB, accounting for the uncertainty due to MW field nonuniformity. Further optimization of Rabi attenuation measurements paves the way for the next-generation quantum-based MW attenuation standards based on qubit Rabi frequency measurements.