Theoretical Investigation Of Laser Cooling And Magneto-optical Trapping Toward The Alkaline-earth-metal Monohydride—CaH Molecule

In the last few decades,the research related to cold atoms has developed rapidly and made substantial progress.Compared with cold atoms,cold molecules have richer internal degrees of freedom and larger molecular dipole moments,therefore contributing to potential applications in quantum information processing,precision measurement,ultracold chemical reactions and quantum many-body physics.As the main approach of preparing cold molecules,laser cooling has been applied in many molecules such as SrF,CaF and YO,and is also under investigation of related research involving MgF,BaF,SrOH,CaOH and so forth.There is a highly diagonalized Frank-Condon factor between X~2?⁺and B~2?⁺of CaH molecule,and it is theoretically possible to be used to laser cooling.Based on this,I focus on the design of the laser cooling scheme of the B~2?⁺?X~2?⁺ transition,given the laser pumping scheme of the B~2?⁺?X~2?⁺ transition and an electro-optical modulation(EOM)scheme covering four hyperfine energy levels of the |X,v=0,N=1,->state.Then,we build the 3D magneto-optical trapping model of CaH molecule magneto-optical trapping.I simulate the damping and trapping forces of CaH molecules in the A~2?_1/2 ?X~2?⁺ and B~2?⁺?X~2?⁺transitions using rate equations,and analyze the cooling and trapping effects of CaH molecules in magnetooptical trapping under the four-frequency component and multi-frequency component laser settings,individually.At the same time,I extend the work to the molecular systems involving the nuclear spin of 3/2,and demonstrate the laser pumping schemes,hyperfine energy structures of the ground states and the EOM sideband modulation schemes of CaCl and CaBr in their A~2?_1/2 ?X~2?⁺ transition,respectively.Although their ground state hyperfine energy structures are more complex than those of CaH and CaF,CaCl and CaBr molecules can still satisfy the requirements of being laser cooled while no dramatic increase in the difficulties of the sideband modulation.Actually,the CaCl molecule only require one single EOM to simultaneously cover six hyperfine energy levels,while the CaBr molecule need two EOMs to do so.It is also found that the linearity of their Zeeman structures is relatively good,thus favorable for realizing the MOT.As a conclusion,the current work not only proves the feasibility of laser cooling and magneto-optical trapping of CaH molecules in both A~2?_1/2 ?X~2?⁺ and B~2?⁺?X~2?⁺transitions,but also provide in detail the laser pumping scheme and the EOM sideband modulation scheme for the latter transition.In addition,the theoretical work can be also of potential reference to theories and experiments related to SrH and BaH molecules,and paves the way to the precision measurement of the electron's Electric Dipole Moment using alkaline-earth-metal monohydrides in laser cooling and magneto-optical trapping,thus further broadening the insights into the search for new physics beyond the Standard Model such as the exploration of CP violation.Also,the current work demonstrates the feasibility of laser cooling toward CaCl and CaBr which possess the nuclear spin of 3/2,and contribute to the theoretical understanding of molecules possessing large nuclear spins toward the laser cooling and trapping application.