Laser Cooling Molecular Candidates

Abstract

Ultracold molecular physics is a promising research field with great potential to revolutionize various important applications such as quantum information. One of the methods that can be used to produce ultracold molecules is laser cooling. This work investigates diatomic molecules that can be cooled through Doppler laser cooling, using quantum computational calculations. The process involves the following steps: determining the molecule's Potential Energy Curves using MOLPRO, determining their corresponding spectroscopic constants using Xpoly, determining the FranckCondon Factors of selected transition between molecular states using LEVEL, calculating their transition dipole moments using MOLPRO, calculating their radiative lifetime using LEVEL, and finally, proposing a suitable laser cooling scheme. Several molecules are introduced in this thesis based on their electronic structure. We confirm that PH molecule can be cooled through Doppler laser cooling with a primary cooling cycle between A3Π – X3Σ- states having 3956 photon absorption/emission. The radiative lifetime of the main transition was found to be 213 ns. Four lasers are proposed for this system: λ00 = 342 nm, λ01 = 370 nm, λ02 = 404 nm, λ03 = 440 nm. We also find that LuF molecule can be laser cooled, with the main cooling cycle between (1)1Π – X1Σ+ states having 15276 photon absorption/emission. The radiative lifetime of the main cycle was deduced to be 9.22 ns. The laser cooling scheme features four lasers: λ00 = 401 nm, λ01 = 411 nm, λ02 = 421 nm, λ03 = 431 nm. To validate our results and account for the uncertainty that they may have, we did sensitivity analysis where we alternate Re and Te values. We found that changes in the experimental parameters are minimal and do not affect our conclusion on the laser cooling feasibility. In addition, we compared our candidates with some of the ones studied in the literature. It showed that our findings are reasonable and building laser cooling apparatus using our results is feasible compared to ones recorded in the literature that have some unfeasible experimental parameters. Finally, SiN was investigated; however, further work is needed to improve its spectroscopic constants and continue investigating its laser cooling feasibility. We recommend that the effect of spin-orbit coupling on PH and LuF PEC's should be studied. Moreover, their investigation as potential qubits in quantum computers should give interesting results. Finally, this work can be expanded to include polyatomic molecules that contain some of the diatomic molecules that were proved feasible for laser cooling and to further help in introducing the ultracold molecules to chemical engineering applications by investigating their reactions in ultracold temperatures.

Date of Award	May 2021
Original language	American English