Theoretical Study On The Structure And External Field Effects Of Two-electron/Divalent Electron Atoms

Helium is the simplest three-body atomic system.The calculations of the atomic structure and measurements of transition frequency of helium play an important role in testing the QED theory,determining fundamental physical constants,and exploring the properties of nuclear structure independent of nuclear model.For example,the fine-structure splitting of the 23P state of helium can be used to test the QED theory.Recently,the combination of theoretical calculation and experimental measurement of the 413 nm tune-out wavelength for the 2 3S state of helium provides a nonenergy test of QED theory.However,there exists 19 ppm discrepancy between the theoretical value and measurement result of the 413 nm tune-out wavelength,which is mainly due to the uncalculated QED contribution.Therefore,carrying out the more detailed QED and nuclear recoil investigations are expected to solve this discrepancy.The alkaline-earth metal atoms are composed of a closed shell core and two valence electrons,which can be regarded as a helium-like three-body system.They are important research objects for the development of high-precision optical frequency standards.At present,the systematical uncertainty of the best Sr lattice clock has achieved to the 10-18 level.Aiming to develop new-generation optical clock,a better understanding and meticulous control of the atom-field interactions would benefit for the realization of higher-precision optical clocks.Therefore,the effects on the systematic uncertainty of optical clocks from the multipolar and higher-order atom-field interaction need to be quantitatively evaluated.In this thesis,the relativistic configuration interaction(RCI)method is developed for the high-accuracy calculation of the tune-out wavelength and magic wavelength of helium.The Dirac-Fock plus core polarization(DFCP)and RCI approaches is combined to calculate the dynamic multipolar polarizabilities and hyperpolarizabilities of the Mg and Sr clocks,in addition,the high-order external field effects are also evaluated.The specific contents are as follows,(1)The relativistic nuclear recoil and QED corrections to the 413 nm tune-out wavelength for the 2 3S1 state of helium are studied.The theoretical prediction of the tune-out wavelength has been realized with high accuracy.However,when we incorporate the retardation correction to compare results with the only current experimental value,there is 1,4? discrepancy between theory and experiment,which stimulates higher precision experimental investigations on the 413 nm tune-out wavelength.In addition,we also determine the QED correction for the static dipole polarizability of the 2 3 S1 state to be 22.5 ppm,which may enable a new test of QED in the future.(2)Using the RCI method and taking into account of the corrections from the finite nuclear mass and QED corrections to the dynamic dipole polarizability of the 2 3S1 and 2 1S0 states of helium,we have determined a series of magic wavelengths around 320 nm for the 23S1?2 1S0 transition.Especially,our predicted magic wavelength of 319.815 3(6)nm for 4He is verified by the recent measurement of W.Vassen's group in Amsterdam Univ.,and the present magic wavelength for 3 He would providc theoretical support for experimentally designing an optical dipole trap.(3)Using the DFCP method,the calculations of the dynamic multipolar polarizabiliy and hyperpolarizability for the alkaline-earth metal ions have been performed.The magic trap drive frequency and magic ellipticity are also determined.Our work provides important theoretical reference for eliminating the scalar Stark shift and secondorder Doppler shift that caused by the micromotion,and the fourth-order Stark shifts which related to the hyperpolarizability.(4)Facing to the great demand of the development of new generation optical clock,we combine the DFCP and RCI methods to calculate dynamic multipolar polarizabilities and hyperpolarizabilities of the Mg and Sr clocks.The lattice light shift against variation of the laser detuning and trap depth is also investigated.For the Mg clock,we find that there exists a distinctive operational magic lattice intensity that reduces the total light shift below 1×10-19 over 14%of the trap depth variatio,which provides important support for the realization of the Mg lattice clock with high precision.For the Sr clock,our differential dynamic hyperpolarizability at the magic wavelength is consistent with existing theoretical and experimental results.Our differential multipolar polarizability is different from recent measurements,which calls for further experimental investigation to resolve this discrepancy.