Towards a Universal Optical Trap for Molecules

We propose a novel approach to optically trapping a wide class of chemical species at cryogenic temperatures, particularly small, closed-shell molecules. The trapping mechanism is insensitive to a molecule's internal state, energy level structure, permanent dipole moment, and magnetic properties. In this "universal" trap, molecules will be thermalized in a helium buffer gas at 1.5 K and trapped optically in a deep dipole trap operating at 1064 nm, which is far red-detuned from any molecular resonances. The ∼10 K trap depth will be produced by a tightly focused buildup cavity capable of reaching intensities of hundreds of GW/cm² [1]. Here, we theoretically investigate the trapping and loading dynamics, as well as the one- and two-body loss rates, and conclude that, as a lower bound, molecules can be trapped for over a second at densities of order 10¹⁰ cm^-3. We show that photo-ionization and photo-dissociation are negligibly small for a large number of candidate molecules. We also report on our progress towards experimentally demonstrating this novel trap. Our trap will open new possibilities in molecular spectroscopy, studies of cold chemical reactions, and precision measurement, amongst other fields of physics.

[1] Rev. Sci. Instrum. 92, 053005 (2021); https://doi.org/10.1063/5.0045496