Theoretical Researches On Molecular Laser Cooling And Magneto-optical Trapping As Well As The Measurement Of The Electron Electric Dipole Moment

After nearly three decades of rapid development,cold atoms techniques have made tremendous achievements and also innovated many frontier fields.However,the rich internal structure of molecules naturally lends itself to diverse and exciting applications,for example,heteronuclear diatomic molecules have permanent electric dipole moments,which can lead to long-range,anisotropic and tuneable dipole-dipole interactions.The combination of the precise control on molecular various freedom degrees and these dipolar interactions makes cold molecules very useful in quantum simulations and quantum computations.Ultracold molecular samples also provide unique environment for studying chemical reaction kinetics and for precision measurement experiments,by which scientists can test the physical fundamental symmetries and explore new physics beyond Standard Model,and so on.But It is difficult to apply cold atoms techniques to neutral molecules due to their more complex internal structures,then a lot of techniques to produce cold molecules have been developed,from adiabatic expansion supersonic molecular beams to buffer gas cooling slow molecular beams;from electrostatic Stark(magnetostatic Zeeman)deceleration to recent molecular laser cooling and magneto-optical trapping,each advancement was full of difficulties and challenges.In this paper,firstly we have focused on molecular electrostatic manipulation,rotational Stark effects of various polyatomic molecules have been studied in detail by the method of matrix diagonalization,which is more accurate than perturbation theory.We have summarized and explained some valuable rules,for example,linear molecules have none first order Stark effect;symmetric top molecules have observable linear Stark effect;all molecular rotational ground states are high-field seeking states;low-field seeking states of heavy-atom molecules can easily turn to high-field seeking states;under all electric fields,there are always twofold degeneracies with ±MJ except for MJ=0,and so on.These results would offer theoretical preparations for our electrostatic manipulation experiments.Afterwards,we have analyzed common Hund's case(a)and(b)in diatomic molecules,and calculated their rotational,fine and hyperfine structures as well as respective Zeeman and Stark effects by the effective Hamiltonian approach.Those processes are very versatile for the same type molecules,which have built theory foreshadowing for the follow-up experiments.Secondly,we have proposed a new laser cooling candidate molecule-24Mg19F radical.Its lifetime of the excited state A2?1/2n and transitional wavelengths are both suitable.We have calculated the Franck-Condon factors and vibrational branching ratios between X and A states by three methods,also investigated the lower X2?+hyperfine manifolds using the efFective Hamiltonian approach,and found that one cooling beam and one repumping beam with their first-order sidebands are enough to complete its effective laser cooling.The couplings of angular momenta and the magnetic properties in MgF hyperfine structure have been analyzed in detail,which would offer preparations for magneto-optical trapping experiments.We also have analyzed the feasibility of laser cooling the 138Baa19F molecule,whose transitional wavelengths can be offered by the cheap semiconductor lasers.The highly diagonal Franck-Condon factors of the main transitions have been verified by three methods,and four lasers would ensure its effective decelaration and laser cooling because of its large mass and small scattering photon momentum.But there is a metastable state A'?between the ground state X2?+ and the excited state A2?1/2,which would fatally destroy the main quasi-cycling ?-? transition for cooling.Then we have analyzed the mixing between A'? and A2?1/2 states,and estimated the lifetime of the state A'?.This leakage problem would be addressed by microwave mixing of the first three rotational levels.And its lifetime(56ns)of A2?1/2 makes frequency-chirped laser cooling practicable.Then we have built a three-dimensional magneto-optical trap(MOT)model,by the rate equations studied how atomic dynamics depended on the angular momenta,g factors of the upper and lower levels and polarization configurations of lasers,and obtained some useful conclusions.Then we have applied the model and conclusions above to MgF system,and found that its restoring force was much weaker than the atomic force in a MOT by three orders of magnitude,so any MgF radicals would not been captured in this MOT because of very small g factor of its upper state.Then we have investigated its dynamics in a different type of MOT,whose magnetic fields and laser polarizations are reversed rapidly and synchronously,called "RF MOT".When the reversing frequency is up to dozens of MHz,the trapping acceleration experienced is nearly same to the atomic acceleration in type-? MOTs,so RF MOT is a good choice for our magneto-optical trapping MgF radical experiments.Finally we have proposed an idea for measuring the electron electric dipole moment by using 208Pb19F radical.We first have discussed the fundamental principle of measuring eEDM based on PbF molecules,then studied external field effects of its fine and hyperfine structures by the effective Hamiltonian approach,and obtained the dependences of the internal effective electric field and the effective g factors on the applied electric field.They have been found that at a typical operating field 10kV/cm,there is large P,T-violation effects in PbF system with an effective electric field 32.36GV/cm;the effective g factors of the even and odd parities F=1 levels within J=1/2 are-0.0221 and 0.0621 respectively.Obviously it is not sensitive to magnetic field fluctuations.Then we have presented Ramsey separated oscillating fields interference scheme for this measurement and also evaluated some statistical and systematic errors.