Resonant Coupling in the Heteronuclear Alkali Dimers for Direct Photoassociative Formation of X(0,0) Ultracold Molecules

TL;DR

This paper investigates pathways for forming ultracold heteronuclear alkali dimers in their ground state using high-quality ab initio calculations, identifying promising resonant couplings and photoassociation strategies for various molecules.

Contribution

It identifies specific resonant couplings and photoassociation pathways that enhance the formation of ultracold heteronuclear alkali dimers in their lowest rovibronic levels.

Findings

Resonant coupling of $2 ^1\Pi$ and $1 ^1\Pi$ states is promising for KRb, RbCs, and less so for KCs.

Coupling of $3 ^1\Sigma^+$ and $1 ^1\Pi$ states is promising for LiNa, LiK, LiRb, and less for LiCs and KCs.

Direct photoassociation near dissociation is promising for NaK, NaRb, and NaCs, with some detuning requirements.

Abstract

Promising pathways for photoassociative formation of ultracold heteronuclear alkali metal dimers in their lowest rovibronic levels (denoted X(0,0)) are examined using high quality ab initio calculations of potential energy curves currently available. A promising pathway for KRb, involving the resonant coupling of the $2 ^1\Pi$ and $1 ^1\Pi $ states just below the lowest excited asymptote (K($4s$)+Rb($5p_{1/2}$)), is found to occur also for RbCs and less promisingly for KCs as well. The resonant coupling of the $3 ^1 \Sigma ^+ $ and $1 ^1\Pi $ states, also just below the lowest excited asymptote, is found to be promising for LiNa, LiK, LiRb, and less promising for LiCs and KCs. Direct photoassociation to the $1 ^1\Pi $ state near dissociation appears promising in the final dimers, NaK, NaRb, and NaCs, although detuning more than 100 cm$^{-1}$ below the lowest excited asymptote may be required.