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APL Photonics

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

Junnan Wang, Lei Hou, Qihui He, Xi Chen, Lei Yang, Wei Shi

Published Apr 1, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1063/5.0320920

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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.
With the rapid advancement of terahertz (THz) technology, there is an urgent demand for highly sensitive, broadband THz detectors that can operate at room temperature to support the evolving applications. Due to the high sensitivity of Rydberg atoms to external electric fields, detectors based on Rydberg quantum coherence offer great potential for highperformance THz detection. This paper proposed a ambient temperature electrometry approach for THz detection using probe laser spectroscopy of Rb Rydberg atoms and carry out a comprehensive study of a four-level system involving electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting in Rb cascades. By solving the Lindblad master equation, the influences of the THz electric field, probe laser, and coupling laser on the populations of the ground and Rydberg states were analyzed. Furthermore, the effects of temperature and vapor cell dimensions on the Rb atomic density are examined, revealing their critical impact on detection sensitivity. The results predict that the proposed quantum coherence based THz detection method can achieve a sensitivity as low as 10−9^{-9}−9V/m/Hz1/2^{1/2}1/2at ambient temperature. This paper provides a solid theoretical foundation for the implementation and optimization of Rydbergatom- based quantum coherence techniques for high-sensitivity, ambient temperature THz wave detection.
As terahertz (THz) technology rapidly develops, room temperature THz detectors with high sensitivity and wide bandwidth are urgently required. Rydberg atoms are very sensitive to external electric fields, and offer a promising approach for THz detection with exceptional sensitivity. In this paper, we propose a method for measuring the THz field with the frequency of 0.17 THz using 85Rb Rydberg atoms. By analyzing the probe laser transmission spectrum and atomic population, the electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effect are explained by the presence and splitting of the Rydberg dark states; the THz field, coupling laser and probe laser play a crucial role in the EIT signal; and the EIT spectral transmission will increase when the atomic population of the excited state decreases. Moreover, a method was demonstrated to improve the THz detection sensitivity by changing the eigenfrequencies of the Rydberg dark states with THz detuning. This work finds the relationship between EIT-AT effect and atomic population of Rydberg atoms caused by THz wave and provides what we believe to be a new method to improve the detection efficiency.
In recent years, terahertz (THz) technology has made significant progress in numerous applications; however, the highly sensitive, room-temperature THz detectors are still rare, which is one of the bottlenecks in THz research. In this paper, we proposed a room-temperature electrometry method for THz detection by laser spectroscopy of cesium ( Cs 133) Rydberg atoms, and conducted a comprehensive investigation of the five-level system involving electromagnetically induced transparency (EIT), electromagnetically induced absorption (EIA), and Autler–Townes (AT) splitting in Cs 133 cascades. By solving the Lindblad master equation, we found that the influence of the THz electric field, probe laser, dressing laser, and Rydberg laser on the ground state atomic population as well as the coherence between the ground state and the Rydberg state, plays a crucial role in the transformation and amplitude of the EIT and EIA signals. Temperature and the atomic vapor cell’s dimensions affect the number of Cs 133 atoms involved in the detection, and ultimately determine the sensitivity. We predicted the proposed quantum coherence THz detection method has a remarkable sensitivity of as low as 10 −9 V m −1 Hz −1/2 . This research offers a valuable theoretical basis for implementing and optimizing quantum coherence effects based on Rydberg atoms for THz wave detection with high sensitivity and room-temperature operation.
A comprehensive study of three-photon electromagnetically induced transparency (EIT) on the cesium (133Cs) cascade is performed. When a THz electric field is applied on the133CS atoms, the EIT peak splits into a doublet, known as Autler-Townes (AT) splitting, and the AT splitting interval is proportional to the strength of the applied THz field. At the same time, we explored the impact of Rabi frequencies of various light fields on EIT-AT signal by numerically solving the Lindblad master equation. Due to the relative simplicity and cryogen-free nature of this system, it has the potential to provide a route to the high-sensitivity detection across the THz frequency range, and provide an alternative to calorimetric methods.
A Rydberg atom detector provides a promising approach for characterizing terahertz (THz) electric fields. Electric field polarization detection is crucial for accurately characterizing THz wave propagation, identifying signal sources and interference, and so on. This paper demonstrates a method for accurate measurement of THz polarization using a four-level cesium Rydberg-atom system. By analyzing the evolution of electromagnetically induced transparency and Autler-Townes spectra under different polarization configurations, the THz polarization angle is quantitatively determined from the relative intensities and asymmetry of the spectral peaks. The results show that the spectral response exhibits a clear dependence on the polarization angle with symmetry about 90°, enabling unambiguous angle determination, and a polarization resolution of 1.28° is achieved. Furthermore, compared with a Schottky diode detector, the proposed method exhibits comparable sensitivity while providing improved fitting consistency and robustness. This approach simplifies both theoretical analysis and experimental implementation for THz polarization measurement, and is promising for applications in THz sensing and spectroscopy.
The bandwidth and sensitivity of traditional terahertz detection devices are limited by material properties and working temperature. Here, we proposed a four-level Rydberg atom detection method, which can realize real-time detection for the absolute strength of the terahertz electric field under room temperature with the detection bandwidth of 0-5 THz. By theoretical analysis and formula derivation, the relation among the terahertz electric field strength, excitation energy level, coupling photoelectric field strength, gas cell temperature and electromagnetically induced transparency (EIT) signal are studied in detailed. The NEP of this method is proven to be 10−17W/Hz1/2in the range of 0-1 THz, which is three orders of magnitude smaller than that of the traditional optimal thermal detection system. This research has important reference value for the later high-sensitivity detection and application development of terahertz waves