The LevT Project

Tunable BEC of cesium and molecular quantum gases

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


Content:  Highlights / Goals / Status / References / Team / Support


Highlights of the LevT Experiment


Goals of the Experiment

The present goals of this experiment are

  1. to map out the exotic molecular spectrum for ultracold Cs dimers and to test for novel molecular states and level crossings which allow precision molecular spectroscopy and the realization of molecule interferometers,
  2. to investigate the interaction properties of ultracold Cs dimers, in particular near scattering resonances, for the synthesis of complex molecules and for new chemistry in the ultracold quantum regime,
  3. to investigate into the properties of Efimov states and to search for Efimov resonances in atom-atom-atom, atom-dimer, and dimer-dimer scattering,
  4. to use ultracold and trapped molecules for precision optical spectroscopy to map out the excited (S+P) molecular structure,
  5. and to test the properties of molecular quantum matter, in particular to investigate the collective hydrodynamic behavior of a molecular superfluid, and to explore the phase transition from an atomic to a molecular BEC.


Status of Research

Ultracold Cs atoms in the hyperfine quantum state F=3, mF=3 feature wide magnetic tunability of their interaction properties. Tuning of interactions is achieved near magnetically induced Feshbach resonances which couple atomic states to high-lying molecular states. It has thus been possible togenerate BECs whose mean field interaction can be tuned over a wide range[1]. In particular, non-interacting BECs in the ideal gas limit can be produced. Also, the coupling to molecular states can directly be exploited toform ultracold dimer molecules out of ultracold samples of Cs atoms, preferably out of a Cs BEC [2]. Within this project, for the case of Cs, these so-called Feshbach dimers have so far been generated near a narrow closed-channel dominated g-wave Feshbach resonance at 20 G, and they have been used to map out the molecular spectrum below the dissociation threshold. In particular, a molecular l-wave state has been identified, and an avoided crossing associated with this state has been used to realize an internal-state molecular interferometer [3]. Moreover, it has been possible to observe Cs2-Cs2collisional resonances as a function of magnetic field strength [4], giving the first indication for a molecular Feshbach resonance where two Cs dimers couple to a Cs4 state. Recently,experimental evidence for Efimov quantum statescould be found in an ultracold gas of thermal Cs atoms [5]. These exotic trimer molecules are formed in the so-called resonant limit when the scattering length is much larger than the extent of the molecular potential, and they lead to greatly enhanced three-body losses when tuned to the three-atom threshold. The observation of the Efimov effect has been facilitated by the fact that inelastic two-body losses are not possible in the state F=3, mF=3.



  1. Bose-Einstein Condensation of Cesium
    T. Weber, J. Herbig, M. Mark, H.-C. Nägerl, and R. Grimm
    Science 299, 232 (2003); published online 5 Dec 2002 (10.1126/science.1079699)
  2. Preparation of a Pure Molecular Quantum Gas
    J. Herbig, T. Kraemer, M. Mark, T. Weber, C. Chin, H.-C. Nägerl, and R. Grimm
    Science 301, 1510 (2003); published online 21 Aug 2003 (10.1126/science.1088876)
  3. `Stückelberg interferometry´ with ultracold molecules
    M. Mark, T. Kraemer, P. Waldburger, J. Herbig, C. Chin, H.-C. Nägerl, R. Grimm,
    Phys. Rev. Lett. 99, 113201 (2007)
  4. Observation of Feshbach-like resonances in collisions between ultracold molecules
    C. Chin, T. Kraemer, M. Mark, J. Herbig, P. Waldburger, H.-C. Nägerl, and R. Grimm
    Phys. Rev. Lett. 94, 123201 (2005)
    . cond-mat/0411258
  5. Evidence for Efimov quantum states in an ultracold gas of cesium atoms
    T. Kraemer, M. Mark, P. Waldburger, J. G. Danzl, C. Chin, B. Engeser, A. D. Lange, K. Pilch, A. Jaakkola, H.-C. Naegerl and R. Grimm
    Nature 440, 315 (2006), cond-mat/0512394

complete list of publications of our group

complete list of theses of our group


The LevT Team

The LevT team within Rudi Grimm's group at the Institut fur Experimentalphysik, University of Innsbruck, Austria:
(from left to right):

Former members:



This project is supported by



last change: 09-09-20 by EH