Fig. 1. Basic principle of the Rydberg atom detection system. (a) Schematic diagram of Rydberg atom system for 0.17 THz detection, which includes the probe laser, dressing laser, and Rydberg laser. All lasers overlap within the Cs133 vapor cell. (b) The five-level energy structure of Cs133. The red, orange, and blue arrows correspond to probe laser, dressing laser, and Rydberg laser excitations, respectively. The green arrow represents the detected THz wave. ΔR is the frequency detuning of the Rydberg laser. (c) Schematic diagram of the EIT signal and EIT-AT signal.

Fig. 2. Impact of the Rabi frequencies of the probe laser on the EIT/EIA signal. (a) Probe laser’s transmission as a function of Rydberg laser detuning ΔR. The different colors represent the applied probe lasers with different Ωp, as labeled in the legend. (b) ρ11 (blue line) and ρ14 (olive dashed line) at different Rabi frequencies of probe laser Ωp. The gray lines refer to the area where ρ14 equals 0. In the calculation, the resonance frequencies of the probe laser, dressing laser, and THz electric field are zero (Δp=Δd=ΔTHz=0) and Ωd=20×2π  MHz, ΩR=3×2π  MHz, and ΩTHz=4×2π  MHz.

Fig. 3. Impact of the Rabi frequencies of the dressing laser on the EIT/EIA signal. (a) Probe laser’s transmission as a function of Rydberg laser detuning ΔR in the region of Ωd=(3–15)×2π  MHz, and the vertical axis is represented by logarithmic coordinates due to the small value of transmittance. (b) EIT/EIA signals within the range of Ωd=(22–26)×2π  MHz. (c) ρ11 as a function of Ωd. (d) ρ11 (blue line) and ρ14 (olive dashed line) vary with Ωd within the range of Ωd=(22–26)×2π  MHz. The gray lines refer to the area where ρ14 equals 0. In the calculation, Δp=Δd=ΔTHz=0 and Ωp=4×2π  MHz, ΩR=3×2π  MHz, and ΩTHz=4×2π  MHz.

Fig. 4. Impact of the Rabi frequencies of the Rydberg laser on the EIT/EIA signals. (a) EIT and EIA curves with a single peak without THz electric field. Inset: the EIT signals at ΩR=1×2π  MHz, ΩR=1.5×2π  MHz, and ΩR=2×2π  MHz. (b) AT splitting curves with the application of the THz electric field (ΩTHz=4.0×2π  MHz). (c) ρ11 as a function of ΩR. The blue curve shows the relationship between ΩR and ρ11 when the Rabi frequency of the THz electrical field is 4.0×2π  MHz. The red-dashed curve represents a variation of ρ11 with respect to ΩR when the THz Rabi frequency is zero. (d) ρ11 (blue line) and ρ14 (olive dashed line) as functions of the ΩR. The gray lines refer to the area where ρ14 equals 0. In the calculation, Δp=Δd=ΔTHz=0 and Ωp=4.0×2π  MHz and Ωd=20×2π  MHz.

Fig. 5. Impact of the Rabi frequencies of the THz electric field. (a) Probe laser’s transmission as a function of Rydberg laser detuning ΔR for different Rabi frequencies of THz electric field in the case of Δp=Δd=ΔTHz=0, Ωp=5×2π  MHz, Ωd=20×2π  MHz, and ΩR=3×2π  MHz. (b) Relationship between AT splitting interval Δf and Rabi frequencies of THz electric field ΩTHz. Black squares denote calculated results of Δf at different ΩTHz, and the red solid line is the fitting curve. The fitting equation is marked in the figure.

Fig. 6. Absolute peaks of the EIT and EIA signals for different probe, dressing, and Rydberg Rabi frequencies. (a) Three-dimensional scatter plot. Red scatters indicate the EIA region, white scatters show transitional area from EIA to EIT, and blue scatters represent the EIT region. (b) Two-dimensional contour fill plot of absolute peak of the EIT and EIA signals versus Ωp and Ωd. (c) Absolute peak of EIT and EIA signals versus Ωp and ΩR. (d) Absolute peak of EIT and EIA signals versus ΩR and Ωd.

Fig. 7. Calculated sensitivity of the Cs133 five-level system. (a) Influence of temperature on the number of atoms in the vapor cell. Inset: tendency of the atomic number in the temperature range of −10°C to 50°C. The red square area denotes the temperature range of 28°C to 29°C. The red line indicates the phase transition region. (b) Impact of temperature on S. Inset: the temperature range of −10°C to 50°C, and the black-square area indicates a temperature range of 28°C to 29°C, where the green line represents the phase transition region. (c) Influence of the vapor cell length on S.