Rydberg Atom-Hased Microwave Sensing

Microwave communication is an important part of modern information technology and has advantages of wide coverage,high transmission rate,and strong anti-interference ability.It is widely used in fields such as wireless communication in radio broadcasting,television,telephone and satellite,medical check and target detection in national defense.It is also an important means and tool for science researches.Microwave receiving antenna is one of the core components of microwave systems and is responsible for converting microwave signals into electrical signals.Traditional microwave detection and reception is based on electronic oscillator antennas and has drawbacks such as large size and narrow working frequency range,which limit the performance and further application of microwave receiving antennas.To overcome these problems,scientists have proposed a new type of microwave sensing technology based on atoms in recent years.This atom-based microwave sensing method uses the characteristics of Rydberg atoms with large orbital radii,dipole moments and polarizability,making it very sensitive to microwave electric fields.It can develop small-volume and wide-working frequency non-metallic microwave antennas.At the same time,since the detection intensity of the microwave electric field is determined by atomic structure parameters and basic physical constants,it also has very important applications in the metrology of microwave electric fields and has been developed to be a natural metrological standard.Based on the feature of Rydberg atom sensitive to microwave field,this thesis shows a two-step laser excitation of rubidium（Rb）Rydberg states to form a ladder-type electromagnetically induced transparency（EIT）and studies Autler-Townes（AT）splitting under the action of microwaves based on which the measurement of microwave electric fields is converted into frequency measurement.Experimentally and theoretically,we mainly focus on the optical and state optimization mechanism of Rydberg atom-based microwave detection.Our research work enclosed in this thesis includes:（1）We study the optical optimization of Rb Rydberg atom-based microwave sensing at a certain selected Rydberg state.Based on the ladder-type EIT of two-step optical excitation of ⁸⁵Rb atoms,under the action of microwave coupling(70S_1/2?70P_3/2,transition frequency 10.68 GHz),the effects of probe laser and coupling laser intensity and local oscillator microwave power and detuning on the optical dynamic response of microwave field detection are studied respectively.The experiment determines the optimal optical and microwave working parameters,where the Rydberg atom EIT-AT spectrum has the best linear dynamic optical response and sensitivity to the microwave field.The experiment shows that the optimal sensitivity at microwave resonance is S=13.69（40）nVcm^-1/Hz^1/2,while a detuning ΔRF=-6 MHz further enhances the sensitivity up to S=12.50（04）nVcm^-1/Hz^1/2.Based on the four-level optical Bloch equation,we also provid a thorough explanation of the underlying physical mechanisms behind the optimization of experimental parameters.（2）By exciting higher Rydberg states,we study the microwave-optical dynamic response of Rb Rydberg atom-based microwave sensing and further improve the sensitivity of microwave measurement.We choose the 78S_1/2 Rydberg state of Rb atoms as the reference quantum state and measured the detection sensitivity under microwave transitions between different neighboring Rydberg states.This verifies the physical mechanism that the higher the Rydberg quantum state,the higher the detection sensitivity under the same optical parameter conditions.Under optimized optical parameter conditions,we obtain a final optimized detection sensitivity of S=5.102（49）nVcm^-1/Hz^1/2.（3）We study the effect of microwave polarization on the sensitivity measurement of Rydberg atom-based microwave sensing.The combination of laser and microwave polarization determines the transition path between atomic energy levels.Different polarization combinations can lead to different spectral characteristics,which in turn affects the dipole moment amplitude and then the microwave sensitivity.Based on the microwave transition 81D_5/2?82P_3/2,when the laser polarizations are along with the microwave electric vector direction,a clear AT splitting occurs on EIT,resulting in an ultra-high detection sensitivity of S=4.150（69）nVcm^-1/Hz^1/2.However,when the laser polarizations are perpendicular to the microwave polarization direction,a complex microwave-coupled AT peak forms with a central peak that does not respond to microwaves.This leads to a detection sensitivity decreased down to S=15.07（14）nVcm^-1/Hz^1/2.It shows that a coincidence of polarization for light and microwave prefers a higher detection sensitivity.In summary,we have performed an experimental and theoretical research on the optimization and sensitivity enhancement of Rydberg atom microwave sensing.It will be helpful for improving microwave detection sensitivity in experiments and the further application of atomic microwave sensing technology in fields such as microwave communication,precision measurement of microwave metrology,astronomical observation,and radar detection technology.