Fig. 1. Radio wave response sensitivity of rubidium atoms in the full frequency band^［50］

Fig. 2. Comparison of measurement sensitivity based on electromagnetically induced transparency with that based on standard quantum limit. (a) Schematic diagram of the ladder type three-level structure of the Rydberg electromagnetic induced transparent sensor; (b) variation of rubidium atomic detection sensitivity with optical depth (dot horizontal curve represents the detection sensitivity value under the quantum standard limit, while the solid line represents the sensitivity value under the electromagnetic induced transparency detection method); (c) contrast value between the measurement sensitivity based on electromagnetically induced transparency and the measurement sensitivity based on the standard quantum limit under different optical depth (solid line represents the calculation result in the ladder three-level structure, and the dotted line represents the calculation result in the three-level $\mathrm{\Lambda }$ structure)^［11］

Fig. 3. Schematic diagram of sensitivity enhancement technology. (a) Optical homodyne device; (b) superheterodyne detection device; (c) schematic diagram of optical repumping energy levels^［46］

Fig. 4. Enhancing detection sensitivity using a resonant cavity. (a) Coupling of Rydberg atoms with microstrip line structures^［29］; (b) coupling of Rydberg atoms with flat plate structures^［28］; (c) coupling of Rydberg atoms with split ring structures^［30］; (d) coupling of Rydberg atoms with optical cavities^［23］; (e) an integrated structure of a ring resonant cavity atomic pool^［52］