Continuous Frequency Microwave Measurement And Application Based On The AC-Stark Effect Of Rydberg Atoms

The precise measurement of microwave electric fields plays an vital role in various fields such as communication,military,remote sensing,defense,and cosmology.With the development of quantum technology,microwave measurement systems based on Rydberg atoms have demonstrated superior performance beyond traditional microwave measurement systems.This measurement approach fundamentally differs from traditional techniques by utilizing the absolute identical nature of particles,and its response performance is accurately correlated with first-principles predictions,resulting in high measurement precision.When the outermost electron of an atom is excited to a highly quantum number orbital,it is called a Rydberg atom,which possesses unique characteristics such as large radius,long lifetime,strong interactions,and high polarizability.They are highly sensitive to electric field disturbances in the environment,making them excellent sensing media for microwave electric field measurements,with broad application prospects and significant research potential.In addition,Rydberg atoms are extensively studied in quantum precision measurement,quantum simulation,quantum entanglement,and the preparation and storage of single-photon sources.The electromagnetic-induced transparency（EIT）spectrum of Rydberg atoms exhibits Autler-Townes（AT）splitting when coupled to microwaves.The splitting interval of the spectrum is proportional to the intensity of the microwave electric field.The measurement results can be traced back to the International System of Units（h）,effectively solving the problem of metrological traceability in traditional microwave measurement techniques.Moreover,due to their quantum properties,Rydberg-based measurement systems avoid the Johnson-Nyquist noise limitations caused by metal antennas and free electron thermal motion,thus offering the potential for measurement sensitivity at the level of shot noise.The electric field measurement method based on EIT-AT spectral splitting is only applicable to microwave resonant or near-resonant transitions between Rydberg states,which leads to a sharp decrease in measurement accuracy for microwave fields that are far off-resonance.In the case of a single Rydberg state,the electric field measurement system based on the EIT-AT method has limitations such as a single microwave frequency response and weak tunability,making it difficult to meet the requirements of practical application scenarios.To address these issues,this study proposes a continuous microwave frequency measurement scheme based on the AC-Stark effect of Rydberg atoms.Building on the foundation of differential atomic measurements,this scheme enables high-sensitivity measurement and communication of continuous-frequency microwave electric fields.The main content and innovations of this thesis are as follows:1.An experimental system was established to achieve continuous frequency measurement of microwave electric fields.The zero-crossing temperature of the ULE cavity（Fineness:100000）was measured,and a measurement method based on Cs atomic saturated absorption spectroscopy frequency standard was proposed.The measured value of the zero-crossing temperature was 25.7°C.The Probe-Detuned Heterodyne(PDH frequency stabilization technology was used to lock the laser frequencies of the detection light and coupling light onto the ULE cavity.The corresponding line width of the Rydberg excitation light was less than 100 k Hz.On this basis,a narrow-line EIT spectrum was obtained,and the noise composition of the laser system was studied.2.Theoretical investigations were conducted on the density matrix equations and eigenanalysis of the three-level and four-level systems of cesium Rydberg atoms.The EIT-AT spectra of Rydberg atoms were obtained,and the projection relationship between the spectral splitting interval and the electric field intensity was determined.The AC-Stark effect of the interaction between non-resonant microwave fields and Rydberg atoms was investigated.Numerical calculations revealed the splitting of degenerate levels of Rydberg atoms in strong external electric fields,the response equation for the external perturbation measurement under both resonant and non-resonant conditions was given.The physical mechanism for measuring arbitrary frequencies was studied,providing a theoretical explanation for the single-frequency response and weak tunability limitations of the measurement system based on the EIT-AT method.3.The novel method of using the AC-Stark effect for continuous microwave frequency measurement was first proposed,which extends the operating frequency point of the Rydberg atom electric field measurement system from single-frequency point measurement under resonance conditions to continuous frequency measurement under non-resonance conditions.By using the heterodyne detection method,the system achieved a minimum detectable electric field of Emin=2.25μV/cm,corresponding to a measurement sensitivity of S=712 n V^-1·cm^-1·Hz^-1,with a linear dynamic response range exceeding 65 d B.The system demonstrated continuous microwave frequency measurements from 2 GHz to 5 GHz without requiring any laser tuning,enabling arbitrary continuous frequency measurements for a single Rydberg state.Under any configuration of experimental conditions,the polarization selectivity of the measurement system for external electric fields is not less than30 d B.4.The instantaneous bandwidth of a microwave measurement system based on Rydberg atoms was investigated,and a time-dependent model of the atomic system evolution dynamics was established.The effect of the excitation light field configuration on the speed of the atomic system reaching steady-state evolution was studied.The relaxation effect of Rydberg dark-state atoms on the instantaneous bandwidth of the system was investigated,and the rate of refreshing the dark-state atoms was accelerated by reducing the atomic interaction region,thereby increasing the system’s instantaneous bandwidth.The communication principle and digital communication based on the Rydberg atom AC-Stark effect were studied and demonstrated.Using images as communication verification examples,weak field communication at continuous frequencies ranging from 0.1 GHz to 5GHz was achieved in a single Rydberg state.Under the current experimental configuration,the system’s communication bandwidth was 230 k Hz,the maximum transmission rate was approximately 238 kbps.Assuming that the channel is available（BER<5%）,the minimum field strength of the actual communication carrier field is 13.52μV/cm.