Pathway toward Optical Cycling and Laser Cooling of Functionalized Arenes

Abstract

Rapid and repeated photon cycling has enabled precision metrology and the development of quantum information systems using atoms and simple molecules. Extending optical cycling to structurally complex molecules would provide new capabilities in these areas, as well as in ultracold chemistry. Increased molecular complexity, however, makes realizing closed optical transitions more difficult. Building on already established strong optical cycling of diatomic, linear triatomic, and symmetric top molecules, recent work has pointed the way to cycling of larger molecules, including phenoxides. The paradigm for these systems is an optical cycling center bonded to a molecular ligand. Theory has suggested that cycling may be extended to even larger ligands, like naphthalene, pyrene, and coronene. Herein, we study optical excitation and fluorescent vibrational branching of CaO-, SrO-, and CaO- and find only weak decay to excited vibrational states, indicating a promising path to full quantum control and laser cooling of large arene-based molecules.

Laser Spectroscopy of Aromatic Molecules with Optical Cycling Centers: Strontium(I) Phenoxides

“…Both SrOPh-3-F and SrOPh-3,4,5-F 3 molecules show VBRs >95% for the transition and >90% for the transition, while SrOPh has the lowest VBR of 82.2% for transition. Due to the predominantly localized excitations and previous benchmarking results, − ,, we find TD-DFT is sufficient to predict VBR trends in SrOPh optical cycling species. However, we find our theoretical calculations still lack important dynamic correlation and spin–orbit coupling which will affect important branching pathways.…”

“…The strong peak with a shift of −300 cm –1 is due to a diagonal decay from the state. The origin of the appearance of when exciting the is unknown but could be due to the collisional relaxation from to followed by fluorescence decay to the ground state . ,, The identification of this feature as originating from the state is further confirmed by the observation of the decay to the stretching mode ν 3 at −534 cm –1 from . The other two weak peaks, −238 cm –1 and −55 cm –1 , are due to the vibrational decay to the stretching mode ν 3 and bending mode ν 2 , respectively.…”

“…In the calcium and strontium phenoxides, transitions to the two lowest electronic states ( and , Figure a) have been proposed for laser cooling, since almost all photon scatters go back to the vibrationless ground state . ,, Figure b shows the measured transition energies of all molecules show a linear correlation with the acid dissociation constants, p K a , of the precursor phenol. This linear trend has recently also been observed for CaOPh-X molecules. , A lower p K a implies higher electron-withdrawing capability of the R–O – ligand, which pulls the single electron away from the Sr atom, making it more ionic and increasing the HOMO–LUMO gap . Also shown are excitation energies calculated by time-dependent density functional theory (TD-DFT) which give a similar trend but systematically undershoot the excitation energies likely due to self-interaction error and approximate treatment of electronic correlation .…”

“…The strong peak with a shift is unknown but could be due to the collisional relaxation from B to A followed by fluorescence decay to the ground state X . 41,46,50 The identification of this feature as originating from the…”

“…45 In the calcium and strontium phenoxides, transitions to the two lowest electronic states (A and B, Figure 1a) have been proposed for laser cooling, since almost all photon scatters go back to the vibrationless ground state X. 39,41,46 Figure 1b shows the measured transition energies of all molecules show a linear correlation with the acid dissociation constants, pK a , of the precursor phenol. This linear trend has recently also been observed for CaOPh-X molecules.…”