Experimental progress toward making ground-state ultracold KRb molecules

We propose a promising route for transferring ultracold $X\,\,^1\Sigma^+$ KRb molecules in high vibrational levels (formed via photoassociation) to the true ground state ($X\,\,^1\Sigma^+$, $v$=0, $J$=0) with two cw lasers. Using pulsed two-color two-photon ionization, we have identified transitions from high-$v$ levels of the $X$ state to the $3 \,\,^1\Sigma^+$ state. Our calculations show that several of the observed $3 \,\,^1\Sigma^+$ vibrational levels have good Franck-Condon factors for emission to $v$=0 of the $X$ state. This makes the $3\,\,^1\Sigma^+$ state a good candidate for the intermediate state in Raman population transfer. Furthermore, using a combination of pulsed resonance-enhanced one-color two-photon ionization and cw laser depletion, we have achieved rotational resolution of these transitions. With the addition of another cw laser to connect the $X$ state $v$=0, $J$=0 level to an intermediate rovibrational level, we expect to selectively produce translationally, vibrationally and rotationally ultracold KRb molecules. This work was supported by NSF.