Preparation of a heteronuclear two-atom system in the three-dimensional ground state in an optical tweezer

We report the preparation of a heteronuclear two-atom system of Rb-87 and Rb-85 in the ground state in an optical tweezer. Dual-species Raman sideband cooling is applied to the two initially separated atoms to eliminate the crosstalk and three-dimensional ground-state probabilities of 0.91(5) for Rb-87 and 0.91(10) for Rb-85 are obtained. We then merge the two atoms into one trap with a species-dependent transport which is achieved by utilizing vector light shifts depending on the magnetic moments of specific atomic states and the trap polarizations. The measurable motional excitations due to merging are 0.013(1) and 0.006(3) axial vibrational quanta for the Rb-87 and Rb-85 atoms, respectively, while no obvious excitation is observed in the radial directions. This two-atom system offers a good starting point for building a single heteronuclear molecule and for investigating few-body physics. It can also be extended to other atomic species and molecules and thus can find application in ultracold chemistry.