An optical system for 3D trapping and photofragmentation of ultracold calcium monohydride molecules
Abstract
Laser cooling and trapping of atoms has developed as the cornerstone of modern atomic physics. The toolbox of atomic cooling techniques has led to quantum computation and simulation platforms as well as atomic clocks. Extending these techniques to molecules is of utmost importance as molecules present significant advantages over their atomic counterparts for a range of scientific goals. Recent progress in the field has resulted in manipulations of single diatomic molecules trapped in optical tweezers, three-dimensional magneto-optical traps (MOTs) of linear tri-atomic molecules, and Sisyphus laser cooling of symmetric-top polyatomic molecules. Motivated by these advances, we are working to extend laser cooling techniques to diatomic hydride molecules, with the goals of obtaining a new class of molecules for ultracold chemistry experiments, and of dissociating these molecules to create ultracold dilute clouds of atomic hydrogen for high-precision spectroscopy and metrology. Our DOD funded research demonstrated initial laser cooling of barium monohydride (BaH) molecules, and of the lighter calcium monohydride (CaH) molecules. The latter are more conducive to creating large ultracold samples due to their stronger coupling to cooling light, if we can control the loss mechanisms. We established that two prospective laser-cooling optical transitions in CaH are highly efficient- a molecule undergoing optical cycling returns to its original state 97-99percent of the time to continue the cycling process. Using this property, we were able to cycle approximately 170 photons per molecule at a rate of 1.6 million photons per second, limited only by interaction time with the light, and observed a laser cooling effect known as Sisyphus cooling. However, creating a MOT of CaH molecules requires scattering well over 10,000 photons per molecule. This is feasible by repumping the first two vibrationally excited states by returning any lost population to the original ground state. Here CaH differs from other laser-coolable diatomic molecules in that the excited states used for cooling are higher in energy than the ground-state dissociation threshold. This leads to a possibility of predissociation, where a molecule breaks up into its constituents even in the absence of light, presenting an obstacle to laser cooling. Due to symmetry considerations this is not an issue for the lower excited state (A) which is the main cooling state, whereas the higher excited state (B) could indeed predissociate (up to the level of 1 in 1,000, as our measurements indicate), posing a slight complication for a MOT since it is an ideal state for repumping. To allow for this possibility, we have considered alternative avenues for moving forward. The immediate next step is to load a CaH molecular MOT, a versatile starting point for ultracold chemistry experiments. We are confident that we can obtain a high-density MOT with the proposed system components that include a radio-frequency magnetic field setup for CaH trapping and a high-power repumping laser. Subsequently, it is necessary to transfer the molecules into a trap where they can be held without scattering any light. Therefore, our proposed system also includes components for an optical dipole trap that uses intense near-infrared laser light. The final phase of the proposal involves performing controlled photo-fragmentation of the molecules in order to obtain cold, optically trapped hydrogen samples, the starting point for high-precision atomic metrology.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 29, 2024
- Source ID
- FA95502310149
Entities
People
- Tanya Zelevinsky
Organizations
- Air Force Office of Scientific Research
- Trustees of Columbia University in the City of New York
- United States Air Force