Detection of long-wavelength signal is of importance for diverse sensing and communication applications. Conventional metal antennas are limited in this regime, particularly when compactness and high sensitivity are both required. Despite intrinsic advantages for electric-field sensing across an ultra-broad range from DC to terahertz, Rydberg atoms still face challenges in practical long-wavelength signal detection, motivating the development of more sensitive and scalable approaches. In this work, we experimentally show that such a signal acting on the Rydberg state can be converted into a polarization variation of the probe laser, and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio of 17% where the Rb 87 atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 μV cm −1 Hz −1/2 in sensitivity and 1.0 μV cm −1 in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.
Detection of long-wavelength signal is of importance for diverse sensing and communication applications. Conventional metal antennas are limited in this regime, particularly when compactness and high sensitivity are both required. Despite intrinsic advantages for electric-field sensing across an ultra-broad range from DC to terahertz, Rydberg atoms still face challenges in practical long-wavelength signal detection, motivating the development of more sensitive and scalable approaches. In this work, we experimentally show that such a signal acting on the Rydberg state can be converted into a polarization variation of the probe laser, and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio of 17% where the Rb 87 atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 μV cm −1 Hz −1/2 in sensitivity and 1.0 μV cm −1 in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.
Recently, Rydberg atom has emerged as an attractive choice to realize quantum sensing of low-frequency electric field. The progress so far has mostly utilized the intensity and phase changes in probe laser and the corresponding detection mechanism still remains classical. Nevertheless, external field acting on the Rydberg state can induce the polarization variation of probe laser in the Rydberg electromagnetically induced transparency (EIT) system embedded in realistic multi-state atoms. We experimentally observe this phenomenon and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio 17\% where the 87Rb atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 μVcm-1Hz-1/2 in sensitivity and 1.0 μV/cm in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.
Rydberg atoms have emerged as a versatile and efficient platform for high-sensitivity quantum sensing of free-space electric fields, with remarkable progress in detecting low-frequency signals. To date, low-frequency Rydberg receivers have relied on a constant bias field, typically realized via intra-cell electrodes or Rydberg plasmas generated by photoelectric effects or inter-atomic interactions. While these approaches improve sensitivity, they suffer from inherent challenges in calibration, long-term stability, and robustness, hindering practical deployment. Here, we propose, design, and experimentally demonstrate a quantum sensing scheme for low-frequency electric signals using modulated auxiliary fields in Rydberg atoms. Unlike conventional methods that employ external DC electric fields that are often fully shielded by adsorbed atom layers on the cell walls, we introduce an AC-field modulation strategy. The incoming low-frequency signal mixes with the auxiliary field, and together they induce Stark shifts of the Rydberg level. These shifts are mapped onto the probe laser via electromagnetically induced transparency (EIT), in a manner analogous to heterodyne detection. We demonstrate a sensitivity of 7.5±2.6μV/(cm⋅Hz1/2) at 5 kHz and a minimal detectable field of 0.26±0.04μV/cm with an integration time of 1000 s. Furthermore, we extend this approach to systematically analyze the performance of generalized auxiliary fields containing multiple frequency components. By virtue of modulated auxiliary field and quantum frequency mixing, our results establish a robust and systematic framework for quantum sensing of low-frequency electric fields with Rydberg atoms, offering improved sensitivity, stability, and immunity to environmental drifts.
An antenna is a key component of E-field signal pickup. However, an antenna has major limitations due to the metal-based probes, the geometry it carries, and the use of metal transmission lines; this can lead to perturbations or disturbance of the fields which limits the precision for field sensing. Rydberg atoms such as Cesium (Cs) or Rubidium (Rb) are utilized for Rydberg sensing. This can be utilized over a large range of frequencies from DC MHz and THz upto (>100 GHz) to measure amplitude, polarization, power, phase, and Angle-of-Arrival of RF Efield. Rydberg sensor detection scheme provides a multitude of applications, including far field characterization using near field or subwavelength imaging, strong RF E-field measurements, weak field detections, mapping of microwave circuitry, Binary Phase Shift Keying (BPSK), Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK) signals, metrology, and radars. Recently, practical RF E-field probes such as the RFP and movable probe have been prototyped for application specific RF sensing and measurement needs, further, antenna and waveguide embedded Rydberg sensors have also been developed. Few limitations in the Rydberg sensing scheme are due to lasers, EIT line-width, earth magnetic effects, photodiode circuit noise, and vapor cell in-homogeneity. The purpose of the review is to brief about the thematic work done across the Rydberg atom domain and its applications as RF E-field sensors. The findings of this review indicate the advantages and applications of Rydberg atom sensing as well as the gaps and uncertainties the scheme carries.
Rydberg atom-based microwave electric field sensing has attracted growing interest owing to its inherent advantages, such as absolute calibration, wideband operability, and compatibility with room-temperature devices. A critical bottleneck that limits sensitivity is the inefficient coupling between the Rydberg atoms and the incident microwave field, particularly when detecting weak signals propagating in free space. Here we propose and experimentally validate a scheme that integrates a horn antenna with a resonant microwave cavity to significantly improve this coupling for free-space signal reception in the S-band. Using a two-photon excitation scheme in a cesium vapor cell, we systematically characterize the sensing performance under three configurations: a bare cell, direct cavity injection, and a cavity coupled to a horn antenna that captures free-space microwave signals over a 1 m distance. In the antenna-coupled cavity configuration, we achieve an optimal sensitivity of 2.33 nV/cm/Hz at the receiving antenna, which corresponds to an enhancement of approximately 17.9 dB compared to the optimized bare vapor cell configuration. Our findings offer a practical and effective route to boost the sensitivity of Rydberg atomic sensors, facilitating their adoption in real-world microwave metrology and wireless communication applications where weak free-space electric fields must be reliably measured.
We demonstrate the measurement of super low-frequency electric field using Rydberg atoms in an atomic vapor cell with inside parallel electrodes, thus overcoming the low-frequency electric-field-screening effect at frequencies below a few kHz. Rydberg electromagnetically induced transparency (EIT) spectra involving 52 D 5/2 state is employed to measure the signal electric field. An auxiliary DC field is applied to improve the sensitivity. A DC Stark map is demonstrated, where the utilized 52 D 5/2 exhibits m j = 1/2, 3/2, 5/2 Stark shifts and splittings. The m j = 1/2 state is employed to detect the signal field because of its larger polarizability than that of m j = 3/2, 5/2. Also, we show that the strength of the spectrum is dependent on the angle between the laser polarizations and the electric field. With optimization of the applied DC field to shift the m j = 1/2 Rydberg energy level to a high sensitivity region and the laser polarizations to obtain the maximum m j = 1/2 signal, we achieve the detection of the signal electric field with a frequency of 100 Hz down to 214.8 µ V/cm with a sensitivity of 67.9 µ V cm −1 Hz −1/2 , and the linear dynamic range is over 37 dB. Our work extends the measurement frequency of Rydberg sensors to super low frequency with high sensitivity, which has the advantages of high sensitivity and miniaturization for receiving super low frequency.
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.