Formation of deeply bound ultracold LiRb molecules via photoassociation near the Li 2S$_{1/2}$ + Rb 5P$_{3/2}$ asymptote

TL;DR

This paper demonstrates the formation of ultracold LiRb molecules in their ground state via photoassociation near a specific atomic asymptote, using spectroscopy to analyze vibrational populations and decay pathways.

Contribution

It provides the first spectroscopic evidence of ground state formation of ultracold LiRb molecules through spontaneous decay after photoassociation near the Li 2S$_{1/2}$ + Rb 5P$_{3/2}$ asymptote.

Findings

Observation of vibrational levels populated in the ground state.

No decay observed to weakly bound levels of certain electronic states.

Deduced a lower bound for the LiRb$^+$ dissociation energy.

Abstract

We present spectra of ultracold $^7$Li$^{85}$Rb molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual species magneto-optical trap (MOT), weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the B$^1\Pi$ state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization (REMPI) to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the observed lines from the spectra are consistent with transitions from the X$^1\Sigma^+$ ground electronic state to either the B$^1\Pi$ or D$^1\Pi$ electronic states that have been previously observed, with levels possibly as low as X$^1\Sigma^+$ $(v'' = 2)$ being populated. We do not observe decay to weakly bound vibrational levels of the X$^1\Sigma^+$ or a$^3\Sigma^+$ electronic states in the spectra. We also deduce a lower bound of 3900 cm$^{-1}$ for the dissociation energy of the LiRb$^+$ molecular ion.