Proposal for the formation of ultracold deeply-bound RbSr dipolar molecules by all-optical methods

TL;DR

This paper analyzes all-optical methods for creating ultracold RbSr molecules, focusing on photoassociation and STIRAP techniques, to facilitate quantum simulation applications.

Contribution

It provides a detailed feasibility study of all-optical schemes for forming ultracold RbSr molecules based on ab-initio calculations.

Findings

Photoassociation rates vary depending on electronic states and proximity to asymptotes.

STIRAP can efficiently produce ground-state molecules in a controlled manner.

Deeply-bound levels are more suitable for stable molecule formation.

Abstract

Ultracold paramagnetic and polar diatomic molecules are among the promising systems for quantum simulation of lattice-spin models. Unfortunately, their experimental observation is still challenging. Based on our recent \textit{ab-initio} calculations, we analyze the feasibility of all-optical schemes for the formation of ultracold $^{87}$Rb$^{84}$Sr bosonic molecules. First, we have studied the formation by photoassociation followed by spontaneous emission. The photoassociation rates to levels belonging to electronic states converging to the $^{87}$Rb$(5s\,^2S)$+$^{84}$Sr($5s5p\,^3P_{0,1,2}$) asymptotes are particularly small close to the asymptote. The creation of molecules would be more interesting by using deeply levels that preferentially relaxes to the $v''=0$ level of the ground state. On the other hands, the photoassociation rates to levels belonging to electronic states converging to the Rb$(5p\,^2P_{1/2,3/2})$+Sr($5s^2\,^1S$) asymptotes have high value close to the asymptote. The relaxation from the levels close to the asymptotes creates weakly-bound molecules in mosty only one vibrational level. Second, stimulated Raman adiabatic passage (STIRAP) achieved in a tight optical trap efficiently creates weakly-bound ground-state molecules in a well-defined level, thus providing an alternative to magnetic Feshbach resonances to implement several schemes for an adiabatic population transfer toward the lowest ground-state level of RbSr. Finally, we have studied STIRAP process for transferring the weakly-bound molecules into the $v''=0$ level of the RbSr ground state.