Intensity-Borrowing Mechanisms Pertinent to Laser Cooling of Linear Polyatomic Molecules

Abstract

A study of the intensity-borrowing mechanisms important to optical cycling transitions in laser-coolable polyatomic molecules arising from non-adiabatic coupling, contributions beyond the Franck–Condon approximation, and Fermi resonances is reported. It has been shown to be necessary to include non-adiabatic coupling to obtain computational accuracy that is sufficient to be useful for laser cooling of molecules. The predicted vibronic branching ratios using perturbation theory based on the non-adiabatic mechanisms have been demonstrated to agree well with those obtained from variational discrete variable representation calculations for representative molecules including CaOH, SrOH, and YbOH. The electron-correlation and basis-set effects on the calculated transition properties, including the vibronic coupling constants, the spin–orbit coupling matrix elements, and the transition dipole moments, and on the calculated branching ratios have been thoroughly studied. The vibronic branching ratios predicted using the present methodologies demonstrate that RaOH is a promising radioactive molecule candidate for laser cooling.

Relativistic coupled-cluster calculations of RaOH pertinent to spectroscopic detection and laser cooling

“…These agree well with the corresponding corrections of 40 cm À1 and 76 cm À1 obtained in our previous multi-state vibronic calculations. 36 We adopt the latter values, since they include the anharmonic contributions. Adding these ZPE contributions to the equilibrium term energies, we recommend the values of 12798 AE 160 cm À1 and 15749 AE 160 cm À1 as the level positions for the vibrational origin transitions for the A 2 P 1/2 -X 2 S and C 2 S-X 2 S electronic transitions, respectively, for spectroscopic detection of RaOH using laser induced fluorescence spectroscopy.…”

“…35 Recent computational studies have also shown that the X 2 Σ ↔ A 2 Π 1/2 transitions in RaOH can serve as efficient optical cycling transitions for laser slowing and cooling. 36 It seems to require fewer repumping lasers to slow a cryogenic RaOH molecular beam sufficiently to be loaded into a magneto-optical trap (MOT) than in the corresponding experiment for CaOH. Note that CaOH is currently the only triatomic molecule that has been laser-slowed in three dimension, loaded into a MOT, 37 sub-Doppler cooled, and loaded into an ODT 38 and optical tweezer arrays.…”

Entanglement Generation of Polar Molecules via Deep Reinforcement Learning

“…For example, a recent theoretical study proposed a general protocol for generating long-lived entangled cluster states using electric dipolar interactions, where the qubits are encoded into nuclear spin-rotational states of polar molecules . On the other hand, numerous experiments on laser cooling and magneto-optical trapping for polar molecules such as CaF, SrF, and YO have been successfully demonstrated in recent years, − paving the way toward the quantum processor built with ultracold molecules.…”

Extending the Large Molecule Limit: The Role of Fermi Resonance in Developing a Quantum Functional Group

“…However, the predicted Franck–Condon factors (FCFs) for these decays are <10 –4 , well below the current detection limit. The observed decay can be explained by an intensity borrowing mechanism, , which arises from anharmonic coupling between the nearly degenerate stretching mode ν 4 and the combination mode consisting of two bending modes, also known as a Fermi resonance. ,, To corroborate Fermi resonance doublets, vibrational perturbation theory (VPT) − was applied on top of anharmonic frequency calculations to predict corrected frequencies and resonance doublets and obtain anharmonic FCFs (see Supporting Information for more details). As seen in the insets of Figures a and b, the predicted separations (vertical blue lines) agree well with the observed vibrational doublets (red traces).…”