Improving bandwidth and sensitivity of Rydberg atom terahertz detectors by frequency detuning

Broadband and sensitive terahertz (THz) detectors are essential for advancing applications in THz technology. Rydberg atoms were proven to be a promising THz detector, but its detection bandwidth and sensitivity still remain challenging. In this paper, a four-level cesium Rydberg atom system was designed, and it can be operated using electromagnetically induced transparency (EIT). Above all, a high-performance THz detection scheme was demonstrated by introducing frequency detuning of the THz wave relative to the atomic resonance and analyzing the asymmetric splitting between the EIT main peak and the off-resonant Autler–Townes (AT) peak. This method exploits the linear dependence of Rydberg eigenfrequencies on THz detuning and allows us to resolve weak THz electric fields even in the nonlinear regime. Furthermore, the probe laser power was found to influence the EIT signal, with low power producing a narrow but weak signal and high power yielding a stronger yet broader signal; therefore, under a probe power of 20 μW, a minimum detectable field of 2.43 V/m at 108.9 GHz was achieved, while a probe power of 500 μW allowed the detection bandwidth to be extended to 14 GHz. That means that the sensitivity was improved by 50% and the bandwidth was improved by three orders compared with the conventional EIT–AT method. Theoretical modeling results based on the Lindblad master equation are consistent with the experimental results. This frequency-detuning-based strategy offers a physically traceable and scalable approach to advancing quantum-enhanced THz sensing under ambient conditions.