Antenna gain reflects the ability to concentrate input power and radiate electromagnetic waves in a specific direction, and is a key indicator for evaluating antenna performance. In this paper, a high-accuracy Rydberg-atom-assisted gain-transfer measurement method is proposed for Ku -band microwave antenna gain calibration. The microwave electric field (E-field) intensity is precisely measured via electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effects. Under the same experimental conditions, the microwave intensity distributions of a standard gain antenna (SGA) and the antenna under test (AUT) are systematically compared, enabling gain calibration of the AUT at 12.007 GHz through the proposed method. Furthermore, a Rydberg atom microwave sensor with multi-level transitions ( \(nD_{5/2}\) - \((n+1)P_{3/2}\) , n =50 \(\sim\) 55), is employed to extend the calibration over a wide frequency range within 12.694 \(\sim\) 17.041 GHz, achieving a measurement uncertainty below 0.38 dB. This work establishes a systematic framework for microwave device calibration, providing both theoretical support and experimental validation for precision metrology of high-performance microwave components.
Antenna gain reflects the ability to concentrate input power and radiate electromagnetic waves in a specific direction, and is a key indicator for evaluating antenna performance. In this paper, a high-accuracy Rydberg-atom-assisted gain-transfer measurement method is proposed for Ku -band microwave antenna gain calibration. The microwave electric field (E-field) intensity is precisely measured via electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effects. Under the same experimental conditions, the microwave intensity distributions of a standard gain antenna (SGA) and the antenna under test (AUT) are systematically compared, enabling gain calibration of the AUT at 12.007 GHz through the proposed method. Furthermore, a Rydberg atom microwave sensor with multi-level transitions ( (nD_{5/2}) - ((n+1)P_{3/2}) , n =50 (\sim) 55), is employed to extend the calibration over a wide frequency range within 12.694 (\sim) 17.041 GHz, achieving a measurement uncertainty below 0.38 dB. This work establishes a systematic framework for microwave device calibration, providing both theoretical support and experimental validation for precision metrology of high-performance microwave components.
Significant progress has been made in atom-based measurements of length, time, gravity and electromagnetic fields in recently years. Rydberg atom-based microwave electric field measurement, using electromagnetically induced transparency (EIT) in room temperature alkali-metal vapors, has been extensively investigated and aroused the broad interest. This approach may establish a new standard for the measurements of microwave (MW) and radio frequency (RF) electric fields.In this review, we describe the work on a new method of measuring electric fields based on quantum interference by using either cesium or rubidium atoms contained in a dielectric vapor cell. Rydberg atoms with principal quantum number n >>1 have large direct current (DC) polarizabilities and microwave transition dipole moments, thereby making them extremely sensitive to external electric fields. Using the Rydberg three-level EIT to detect the level splitting and shift that is induced by the external field, we can realize a rapid and robust self-calibration method of measuring the electric field in a frequency range from 0.01 GHz to 1000 GHz. For the MW electric field (frequency range > 1 GHz), the MW field causes the Rydberg states to split, known as an Autler-Townes splitting (A-T) effect when the applied microwave can resonate with adjacent Rydberg states. The MW coupled A-T splitting is proportional to the applied electric field strength, from which the field strength is measured. Using the EIT window, a high sensitivity of 3 μV·cm-1·Hz-1/2 and small electric field of 1 μV/cm are expected to be achieved with a modest setup, and the limitations of the sensitivity are also addressed in the review. For the RF field at frequency mj EIT lines, and avoided crossings formed with the fine-structure levels of equal mj and different J's, which is used to calibrate and measure the RF field amplitude. On the other hand, the dependence of the EIT-line strength on the RF field polarization provides a fast and robust polarization measurement of RF fields based on matching experimental data with a theoretical simulation. The measurements of minimum strengths and sensitivity of RF fields based on Rydberg atoms are one order magnitude below the values obtained by traditional antenna methods. The atom-based field measurement paves the way for determining fields through calibration-free, invariable atomic properties and miniaturization. We also propose its various potential applications in the future.
The Rydberg-based microwave detection is an all-optical technology that uses the strong coherent interaction between Rydberg atoms and microwave field. Different from the traditional microwave meter, the Rydberg atomic sensing is a new-type microwave detector that transforms the microwave spectrum into a coherent optical spectrum, and arouses increasingly the interests due to its high sensibility. For this kind of sensor, the coherence effect induced by coupling atoms with microwave plays a key role, and the decoherence may reduce the sensitivity. A multi-level Rydberg atomic scheme with optimized quantum coherence, which enhances both the bandwidth and the sensitivity for 4 GHz microwave sensing, is demonstrated experimentally in this work. The enhanced quantum coherence of Rydberg electromagnetically induced transparency (EIT) and microwave induced Autler-Townes (AT) splitting in EIT windows are shown using optical pumping at D1 line. The enhanced sensitivity at 3.4 GHz with 0.3 GHz bandwidth can be realized, based on the enhanced EIT-AT spectrum. The experimental results show that in the stepped Rydberg EIT system, the spectral width of EIT and microwave field EIT-AT can be narrowed by optical pumping (OP), so the sensitivity of microwave electric field measurement can be improved. After optimizing the EIT amplitude and adding single-frequency microwaves, the sensitivity of the microwave electric field measurement observed by the AT splitting interval is improved by 1.3 times. This work provides a reference for utilizing atomic microwave detection.
The Rydberg-based microwave detection is an all-optical technology that uses the strong coherent interaction between Rydberg atoms and microwave field. Different from the traditional microwave meter, the Rydberg atomic sensing is a new-type microwave detector that transforms the microwave spectrum into a coherent optical spectrum, and arouses increasingly the interests due to its high sensibility. For this kind of sensor, the coherence effect induced by coupling atoms with microwave plays a key role, and the decoherence may reduce the sensitivity. A multi-level Rydberg atomic scheme with optimized quantum coherence, which enhances both the bandwidth and the sensitivity for 4 GHz microwave sensing, is demonstrated experimentally in this work. The enhanced quantum coherence of Rydberg electromagnetically induced transparency (EIT) and microwave induced Autler-Townes (AT) splitting in EIT windows are shown using optical pumping at D1 line. The enhanced sensitivity at 3.4 GHz with 0.3 GHz bandwidth can be realized, based on the enhanced EIT-AT spectrum. The experimental results show that in the stepped Rydberg EIT system, the spectral width of EIT and microwave field EIT-AT can be narrowed by optical pumping (OP), so the sensitivity of microwave electric field measurement can be improved. After optimizing the EIT amplitude and adding single-frequency microwaves, the sensitivity of the microwave electric field measurement observed by the AT splitting interval is improved by 1.3 times. This work provides a reference for utilizing atomic microwave detection.
A novel antenna gain measurement method based on quantum interaction of highly excited alkali Rydberg atoms and radiated radio frequency electric field from an antenna under test is proposed in this letter. The method allows gain value to be determined by measuring RF field induced splitting frequency of an electromagnetically induced transparency window, antenna feeding power, and finite measurement range. The antenna gain measurement for a K -band standard gain horn antenna is presented to demonstrate the measurement setup and process, and the results are consistent with conventional measurements. The method is promising due to its advantages of simplicity, accuracy, and low cost. This work is of major significance for developing atom-based RF field and antenna characterization.
The determination of the angle of arrival (AoA) of Ku-band microwave signals is of great significance in satellite communications, spectrum monitoring, and national defense security, which has created an urgent demand for high-precision and interference-resistant passive detection techniques. In this study, we propose a Rydberg-atom-based passive measurement method for estimating the AoA of Ku-band incident signals. Based on well-established quantum optical techniques, the proposed method converts the EIT-AT splitting intervals induced by waves or signals incident from different directions in Rydberg atoms within a single vapor cell into the electric-field intensity at the atomic sensor. An electric-field-intensity-angle response model is then established for AoA estimation of a 13.6 GHz wave or signal. Simulation results demonstrate that the proposed method can determine the incident direction within a certain angular range, with an estimation error of less than 3.8°. Without the need for self-calibration and free from interference caused by actively emitted probing electromagnetic waves or reference electric fields, the proposed approach enables AoA determination of incident waves or signals using a single vapor cell with a length of 5 cm.
Atom in Rydberg state has large polarizability, large electric dipole and low ionization threshold field. It is very sensitive to electric field, therefore it can be used to measure the amplitude of electric field, especially the microwave electric field. The new developed scheme is based on quantum interference effects (electromagnetically induced transparency and Autler-Townes splitting) in Rydberg atoms. Instead of the direct amplitude measurement, this method tests the Rabi frequency value of the transmission spectrum which is determined by the microwave electric field strength and the corresponding atom nature. The minimum measured strengths of microwave electric fields are far below the standard values obtained by traditional antenna methods. Compared with the traditional methods, this new scheme has several advantages, such as self-calibration, non-perturbation to the measured field and independence of the probe length. Besides, this scheme can also be used to measure the polarization direction of microwave electric field and realize sub-wavelength imaging. Through adjusting the wavelength of coupling laser, a broadband 1-500 GHz microwave electric field measurement can be achieved. This new scheme is benefitial to conducting the continue electric field measurement and the miniaturization of the test equipment. In this paper, the researches about using Rydberg atom to measure electric field with high precision are reviewed. The basic theory and experimental techniques are introduced. Finally, we discuss a promising method of using Rydberg atom interferometer to detect the accumulated phase in the process of interaction between electric field and Rydberg atoms. This method converts amplitude measurement into phase test, which may improve the precision and sensitivity.