Fig. 1. (a) Four-level diagram of Rb Rydberg atom used to sense microwave electric field;(b) Schematic diagram of experimental setup^[22]

Fig. 2. (a) Experimental setup used to measure 100 Hz electric field; (b) Measurement result ^[26]

Fig. 3. Electromagnetic shielding effect under low-frequency electric field

Fig. 4. The amplitude spectrum of the kHz electric field measured by atomic antennas^[27]

Fig. 5. (a) Experimental setup for measuring strong electric field; (b) Sidebands of atomic energy levels under a strong electric field ^[28].

Fig. 6. Experimental (a) and calculated (b) spectral maps of the 60S_1/2 state modulated by 50 MHz RF field^[28]

Fig. 7. (a) Level diagram used to measure 30 MHz electric field; (b) Experimental setup;(c) Dependence of signal transmission power on measurement sensitivity^[31]

Fig. 8. (a) Experimental apparatus used to measure kHz electric field; (b) Measurement result