All-optical Measurement Of The Lifetime Of Ultracold Rydberg Atoms

Rydberg atoms,one electron of atoms is excited in states with high principal quantum number.They have great applications in quantum sensing,quantum information,quantum simulation,electric field measurement,microwave field measurement,ultracold plasma and other fields due to their unique properties,such as large atomic radius and polarizability,strong coupling with external field and long radiative lifetimes,etc.The lifetime measurements of Rydberg atoms are not only of great importance for the theoretical calculation of dipole matrix elements,oscillator strengths and polarizability,but also for the accuracy test of wave functions,the study of blackbody radiation and the determination of photoionization rates.In this thesis,we demonstrate one all-optical method to measure the radiative lifetime of ultracold Cs Rydberg atoms.This method is based on photodetection of one ground state atomic absorption in a ladder-type electromagnetic induced transparency(EIT),which contains one ground state,one intermediate state and one Rydberg state.In the presence and absence of optical pumping between the Rydberg state and the intermediate state,the absorption of ground state is different and it is used to reconstruct the population of target Rydberg state with delay time.We then apply this method to measure the radiative lifetime of ultracold Cs Rydberg atoms in50S_1/2 and 50D_5/2states.This method is simplified to operate and does not require to quantify the number of ground state atoms,which can be widely used to measure the radiative lifetimes of other Rydberg atoms.The main research contents of this thesis are as follows:Firstly,we set up the experimental scheme and capture the ultracold Cs atoms to the ground state through a magneto-optical trap(MOT).We prepare ultracold Rydberg atoms via 6S_1/2?6P_3/2?50S_1/2/50D_5/2 and obtain experimental parameters of pump laser(coupling laser)and probe laser in excitation process and optical pumping process by optimizing the tests.Secondly,on the basis of the first item,we record the evolution curve of probe laser intensity with time in 50S_1/2 when delay time t_s=0?s via photoelectric detecting technique.Similarly,we also obtain the evolution curve of the depumped intensity with time in 50S_1/2 when t_s=0?s,16?s,and 32?s.Finally,it is reconstructed the evolution curve of target Rydberg atoms with delay time by measuring depumped Rydberg population.The radiative lifetimes of 50S_1/2 and 50D_5/2 are measured by means of exponential fitting.The innovations of this work are as follows:Firstly,for the purpose of reducing the fluctuation of the detected signal caused by atomic instability,we introduced a reference beam.The desirable signal is the subtraction between the probe beam and the reference beam.It is proved that the signal-to-noise ratio is improved by this way.Secondly,the all-optical method shown in this paper is a low-cost,easy-to-operate and efficient measurement method.With the help of this method,we do not need to calibrate the number of initial ground state atoms,rather,we only need to record the changes in the intensity of the probe laser in the presence and absence of optical pumping.We directly evaluate the depumped population of Rydberg atoms by monitoring the changes of probe laser intensity under the two conditions,and the result can reflect the target population of Rydberg atoms.