Quantum gas of deeply bound ground state molecules

Danzl, J.G. and Haller, Elmar and Gustavsson, M. and Mark, M.J. and Hart, R. and Bouloufa, N. and Dulieu, O. and Ritsch, H. and Nägerl, H.-C. (2008) Quantum gas of deeply bound ground state molecules. Science, 321 (5892). pp. 1062-1066. ISSN 0036-8075

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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.