Formation of deeply bound ultracold Sr_2 molecules by photoassociation near the ^1S + ^3P_1 intercombination line

TL;DR

This paper predicts a feasible method to form deeply bound ultracold Sr_2 molecules via photoassociation near the ^1S + ^3P_1 line, leveraging spin-orbit interactions to enable transitions to ground states for precision measurements.

Contribution

It introduces a novel theoretical approach using ab initio calculations to enable formation of deeply bound Sr_2 molecules through photoassociation near an intercombination line.

Findings

Strong spin-orbit interaction facilitates bound-to-bound and free-to-bound transitions.

Photoassociation probabilities are comparable to previously observed weakly bound states.

Method enables production of ground state molecules for fundamental physics experiments.

Abstract

We predict feasibility of the photoassociative formation of Sr_2 molecules in arbitrary vibrational levels of the electronic ground state based on state-of-the-art ab initio calculations. Key is the strong spin-orbit interaction between the c^3\Pi_u, A^1\Sigma_u^+ and B^1\Sigma_u^+ states. It creates not only an effective dipole moment allowing free-to-bound transitions near the ^1S + ^3P_1 intercombination line but also facilitates bound-to-bound transitions via resonantly coupled excited state rovibrational levels to deeply bound rovibrational levels of the ground X^1\Sigma_g^+ potential, with v" as low as v"=6. The spin-orbit interaction is responsible for both optical pathways. Therefore, those excited state levels that have the largest bound-to-bound transition moments to deeply bound ground state levels also exhibit a sufficient photoassociation probability, comparable to that of the lowest weakly bound excited state level previously observed by Zelevinsky et al. [Phys. Rev. Lett. 96, 203201 (2006)]. Our study paves the way for an efficient photoassociative production of Sr_2 molecules in ground state levels suitable for experiments testing the electron-to-proton mass ratio.