Electromagnetically induced transparency spectroscopy of cesium Rydberg atoms in radio-frequency fields

The large electric dipole moment of the Rydberg atom allows strong coupling to weak electric fields and is widely used in electric field measurements because of its reproducibility, precision and stability. The combination of Rydberg atoms and electromagnetically induced transparency (EIT) technology has been used for the detection and characterisation of radio-frequency (RF) electric fields． In this work, the preparation of the Rydberg state (49P_3/2) of the Cs atom was achieved using three-photon excitation with a scheme of all-infrared light excitation of the Rydberg atom by selecting the probe light (852 nm), the dressing light (1470 nm) and the coupling light (780 nm). We have experimentally observed the electromagnetically induced transparency (EIT) spectra of the Rydberg states decorated with radio-frequency electric fields, which optically detects Rydberg atoms. The effect of the amplitude and frequency of the RF electric field on the spectrum is explored in the light of changes in the EIT spectrum. It has been demonstrated that in the region of weak electric field amplitude, only the ac Stark energy shift and spectral broadening occur. As the electric field is further enhanced, the sideband phenomenon occurs in both the primary and secondary peaks of the EIT. In the region of strong field, the Rydberg energy level produces a series of Floquet states with higher-order terms, as well as state shifting and mixing, resulting in asymmetry in the spectra of the EIT sideband peaks. We further discuss the study of the effect of frequency on the shielding effect of the Cs vapor cell based on the shift of the main peak of the EIT. The demodulation of the electric field in the range of 50 Hz ~ 1 kHz with a fidelity of 95% is achieved by using the modulation of the low-frequency electric field to the RF electric field. The results can provide valuable references for spectral detection and traceable measurements of low-frequency electric fields.