Dark resonances for ground-state transfer of molecular quantum gases.

One possible way to produce ultra-cold, high-phase-space-density quantum gases of molecules in the rovibronic ground state is given by molecule association from quantum-degenerate atomic gases on a Feshbach resonance and subsequent coherent optical multi-photon transfer into the rovibronic ground state. In ultra-cold samples of Cs₂ molecules, we observe two-photon dark resonances that connect the intermediate rovibrational level | v=73, J=2〉 with the rovibrational ground state | v=0, J=0〉 of the singlet X¹ Σ ground-state potential. For precise dark resonance spectroscopy we exploit the fact that it is possible to efficiently populate the level | v=73, J=2〉 by two-photon transfer from the dissociation threshold with the stimulated Raman adiabatic passage (STIRAP) technique. We find that at least one of the two-photon resonances is sufficiently strong to allow future implementation of coherent STIRAP transfer of a molecular quantum gas to the rovibrational ground state | v=0, J=0〉. [ABSTRACT FROM AUTHOR]