Ultracold Triplet Molecules in the
Rovibrational Ground State

Institut für Experimentalphysik,
University of Innsbruck, and
Austrian Academy of Sciences,
Innsbruck, Austria

The quest for ultracold ground state molecules

Standard laser cooling techniques as developed for atoms do not work for molecules due
to their complex internal structure. Other pathways to cold and dense samples of molecules are required, such as Stark deceleration and sympathetic cooling or association of ultracold
atoms. Association via Feshbach resonances has directly produced quantum degenerate or near degenerate ultracold molecular gases, but only in very weakly bound states with a high vibrational quantum number. Furthermore, such molecules are in general unstable when colliding with each other, particularly if they are composed of bosonic atoms.


The weakly bound Feshbach molecules (upper image) are transferred into the rovibrational ground state with a STIRAP laser pulse.

Very recently optical schemes have been developed to selectively produce cold and dense samples of deeply bound molecules in the ro-vibrational ground state, but this goal has not been reached yet. We report here the optical transfer of 87Rb2 Feshbach molecules to a single quantum level in the ro-vibrational ground state of the Rb2 triplet potential (a 3Σu+ ), entering the regime of an ultracold and dense ensemble of tightly bound molecules [1].


Potential curves of the ground (a 3Σu+) and excited (3Σg) molecular triplet potential.

The transfer is carried out in a single step using stimulated Raman adiabatic passage (STIRAP) with an efficiency of almost 90%, which is only technically limited. The molecules are held in a 3D optical lattice in which they exhibit a trap lifetime exceeding 200 ms, after an initial relaxation within 50 ms.

Our results have been published in Physical Review Lettersl, Lang et al., PRL 2008,


Physics viewpoint

Simon Cornish from the university of Durham has written a viewpoint article on our and  related work: S. Cornish, Physics 1, 24 (2008).


Innsbruck press release

See here.


The research team

This research was carried out by the Rb-team in the Group of Rudi Grimm under the scientific lead of Johannes Hecker Denschlag.



from left to right: R. Grimm, J. Hecker Denschlag, Tetsu Takekoshi, F. Lang, K. Winkler & C. Strauss



[1] Ultracold Molecules in the Ro-Vibrational Triplet Ground State
F. Lang, K. Winkler, C. Strauss, R. Grimm and J. Hecker Denschlag
Phys. Rev. Lett. 101, 133005 (2008), pre-print: arXiv:0809.0061


We are supported by the Austrian Science Fund (Fonds zur Förderung der wissenschaftlichen Forschung, FWF) in the frame of the Spezialforschungsbereich F15 "Control and Measurement of Coherent Quantum Systems" and by the European Union in the frame of the Cold Molecules TMR Network.



last change: 08-09-27 by FL