Simulations of the bichromatic force in multilevel systems

TL;DR

This paper presents detailed numerical simulations of bichromatic forces in multilevel systems, demonstrating their potential for rapid deceleration and cooling of molecules like CaF without complex repumping schemes.

Contribution

It provides a comprehensive numerical modeling approach for multilevel systems and evaluates simplified models, advancing the understanding of bichromatic force applications in complex atoms and molecules.

Findings

Deceleration of CaF molecules to near rest within 1 cm without repumping.

Simplified models nearly match full 16-level simulations in accuracy.

2-level estimates are only useful for order-of-magnitude predictions.

Abstract

Coherent optical bichromatic forces have been shown to be effective tools for rapidly slowing and cooling simple atomic systems. While previous estimates suggest that these forces may also be effective for rapidly decelerating molecules or complex atoms, a quantitative treatment for multilevel systems has been lacking. We describe detailed numerical modeling of bichromatic forces by direct numerical solution for the time-dependent density matrix in the rotating-wave approximation. We describe both the general phenomenology of an arbitrary few-level system and the specific requirements for slowing and cooling on a many-level transition in calcium monofluoride (CaF), one of the molecules of greatest current experimental interest. We show that it should be possible to decelerate a cryogenic buffer-gas-cooled beam of CaF nearly to rest without a repumping laser and within a longitudinal distance of about 1 cm. We also compare a full 16-level simulation for the CaF B$\leftrightarrow$X system with a simplified numerical model and with a semiquantitative estimate based on 2-level systems. The simplified model performs nearly as well as the complete version, whereas the 2-level model is useful for making order-of-magnitude estimates, but nothing more.