Ultracold LiCs molecules in the absolute ground state X1Sigma+, v'' = 0, J'' = 0 are formed via a single photoassociation step starting from laser-cooled atoms. The selective production of v'' = 0, J'' = 2 molecules with a 50-fold higher rate is also demonstrated. The rotational and vibrational state of the ground state molecules is determined in a setup combining depletion spectroscopy with resonant-enhanced multiphoton ionization time-of-flight spectroscopy. Using the determined production rate of up to 5 x 10(3) molecules/s, we describe a simple scheme which can provide large samples of externally and internally cold dipolar molecules.

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Molecular cooling techniques face the hurdle of dissipating translational as well as internal energy in the presence of a rich electronic, vibrational, and rotational energy spectrum. In our experiment, we create a translationally ultracold, dense quantum gas of molecules bound by more than 1000 wave numbers in the electronic ground state. Specifically, we stimulate with 80% efficiency, a two-photon transfer of molecules associated on a Feshbach resonance from a Bose-Einstein condensate of cesium atoms. In the process, the initial loose, long-range electrostatic bond of the Feshbach molecule is coherently transformed into a tight chemical bond. We demonstrate coherence of the transfer in a Ramsey-type experiment and show that the molecular sample is not heated during the transfer. Our results show that the preparation of a quantum gas of molecules in specific rovibrational states is possible and that the creation of a Bose-Einstein condensate of molecules in their rovibronic ground state is within reach.

We report the successful production of an ultracold sample of absolute ground-state ^{23}Na^{87}Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 10^{11}  cm^{-3}. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state ^{23}Na^{87}Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state ^{23}Na^{87}Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.

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We present a combined experimental and theoretical study of cold reactive collisions between lasercooled Ca + ions and Rb atoms in an ion-atom hybrid trap. We observe rich chemical dynamics which are interpreted in terms of non-adiabatic and radiative charge exchange as well as radiative molecule formation using high-level electronic structure calculations. We study the role of light-assisted processes and show that the efficiency of the dominant chemical pathways is considerably enhanced in excited reaction channels. Our results illustrate the importance of radiative and non-radiative processes for the cold chemistry occurring in ion-atom hybrid traps.Over the past few years, impressive progress has been achieved in the study of reactive collisions at ultralow energies. Recent landmark studies using neutral molecules highlighted the distinct quantum character of reactive processes in this regime and demonstrated new approaches for an unprecedented control of molecular collisions [3,4]. Ion-neutral reactions are another class of processes which exhibit different long-range interactions and therefore a different chemical behavior in comparison to neutrals [5][6][7][8][9][10][11]. With the development of hybrid traps in which laser-cooled atomic ions stored in a radiofrequency ion trap are combined with ultracold neutral atoms in a magneto-optical trap [12][13][14] or a BoseEinstein-condensate [15,16], the study of ion-neutral reactions in the energy range between 1 and 10 −3 Kelvin (usually termed the "cold" regime) has recently become possible. Under these conditions, only a few partial waves contribute to the collision so that resonance as well as radiative effects can become important [5,6,10,17].One key question pertains to the types of chemical processes which can occur in hybrid traps. So far, either fast near-resonant homonuclear charge exchange (in Yb-Yb . For Rb-Yb + , the latter observation was rationalized in terms of radiative and non-radiative charge exchange [18]. The feasibility of molecular-ion formation has also been considered, and evidence for a radiative mechanism has recently been found in the Ca-Yb + system [14]. However, a general understanding of the interplay between these reactive processes and in particular the role of light remains to be established.In the current study, we present a combined experimental and theoretical study of ion-neutral reactive collisions in a Rb-Ca + hybrid trap. Our experimental results are interpreted using high-level electronic structure calculations of the CaRb + potential energy curves (PECs) up to the twenty-second dissociation limit. We observe rich chemical dynamics which we rationalize in terms of nonadiabatic and radiative effects. We show that the efficiency of the dominant chemical processes (radiative molecule formation, radiative and non-radiative charge exchange) is considerably enhanced in excited reaction channels populated in the presence of radiation. Using Rb-Ca + as a model system, our results illustrate the reactive processes which can occu...

The methods producing cold molecules from cold atoms tend to leave molecular ensembles with substantial residual internal energy. For instance, Cs 2 molecules initially formed via photoassociation of cold Cs atoms are in several vibrational levels, v, of the electronic ground state. Here we apply a broadband femtosecond laser that redistributes the vibrational population in the ground state via a few electronic excitation -spontaneous emission cycles. The laser pulses are shaped to remove the excitation frequency band of the v = 0 level, preventing re-excitation from that state. We observe a fast and efficient accumulation, ∼ 70% of the initially detected molecules, in the lowest vibrational level, v = 0, of the singlet electronic state. The validity of this incoherent depopulation pumping method is very general and opens exciting prospects for laser cooling and manipulation of molecules.

A few typing errors are corrected in Tables II and III of the quoted paper. In addition, we included an exhaustive list of sets of cut-off radii used by various authors in their effective core polarization potentials. Indeed the final results are very sensitive to the initial adjustment of atomic energies, and such a report should guide the interested readers through the corresponding literature. Moreover, it is emphasized that the values of cut-off parameters strongly depend on the chosen Gaussian basis set.