Ultracold Bose-Fermi mixtures

The ability to tune the interaction of ultracold quantum gases makes them paradigms for the investigation of quantum many-body effects as they appear throughout nature. Using a mixture of ultracold Cesium-133 atoms (bosons) and Lithium-6 atoms (fermions), we investigate the quantum statistical properties of these mixtures, including the transition to a Bose-Einstein condensate (BEC) or a degenerate Fermi gas (DFG), as well as new effects which arise when the inter-species interaction is controlled.

Ultracold mixture of 6Li and 133Cs

The experimental realization of Bose-Einstein condensates and degenerate Fermi gases has paved the way to study models and theories for quantum phenomena. We apply techniques of laser cooling and trapping of ultracold neutral atoms to create ultracold mixtures at sub micro-Kelvin temperatures. When the collisional properties of the gas are tuned via an external magnetic field close to a Feshbach resonance the gas can enter strongly-interacting regimes which would enable the investigation of universal few- and many body physics or the formation of highly excited LiCs molecules.

In our new experimental setup Cs atoms and Li atoms are decelerated in a double-species Zeeman slower before they a captured in a MOT. For further cooling of Li we use evaporative techniques in a 200 W crossed optical dipole trap. In the case of Cs degenerate Raman sideband cooling provides low temperatures. Currently we hold the mixture of Li and Cs in the optical dipole trap and then switch on magnetic fields up to 1200 G to control the collisional properties.

Latest news and research results

Observation of dipolar splittings of Li-6 p-wave Feshbach resonances: paper published in Phys. Rev. A (Rapid Comm.)11.11.2019
Eleonora Lippi

Our paper on the "Observation of dipolar splittings in high-resolution atom-loss spectroscopy of Li-6 p-wave Feshbach resonances" got published this month in Phys. Rev. A Rapid Communications! We observed dipolar splitting in Li-6 p-wave Feshbach resonances by high-resolution atom-loss spectroscopy. The observed splittings are in very well agreement with coupled-channel calculations.

Reference:
M. Gerken et al., Observation of dipolar splittings in high-resolution atom-loss spectroscopy of Li-6 p-wave Feshbach resonances, Phys. Rev. A (Rapid Comm.) 100, 050701, (2019), or see our full list of publications
PhD-Meeting "FOR2247: From few to many body physics with dipolar quantum gases", 22-24.10 Heidelberg16.10.2018
Eleonora Lippi

From 22nd to 24th of October 2018 the PhD-Meeting of the Forschergruppe "FOR2247: From few to many-body physics with dipolar quantum gases" will take place at the Internationales Wissenschaftsforum Heidelberg (IWH) in Heidelberg. During the meeting, we are honoured to have lectures given by Prof. Dr. Tilman Esslinger and Prof. Dr. Olivier Dulieu concerning long-range interactions in systems of cavity-confined ultracold atoms and ultracold polar molecules.

For more information:
Website: FOR2247


A detailed analysis of the role of the intraspecies scattering length in the Efimov scenario has been published in Phys. Rev. A07.07.2017
Stephan

In a joint experiment and theory work we study the effect of the intraspecies scattering length onto the heteronuclear Efimov scenario, following up on our earlier observation of Efimov resonances in an ultracold Cs-Li mixture for negative and positive Cs-Cs scattering length. Three theoretical models of increasing complexity are employed to quantify its influence on the scaling factor and the three-body parameter: a simple Born-Oppenheimer picture, a zero-range theory, and a spinless van der Waals model. These models are compared to Efimov resonances observed in an ultracold mixture of bosonic 133Cs and fermionic 6Li atoms close to two Cs-Li Feshbach resonances located at 843 G and 889 G, characterized by different sign and magnitude of the Cs-Cs interaction. By changing the sign and magnitude of the intraspecies scattering length different scaling behaviors of the three-body loss rate are identified, in qualitative agreement with theoretical predictions. The three-body loss rate is strongly influenced by the intraspecies scattering length.

Reference:
S. Häfner et al., Role of the intraspecies scattering length in the Efimov scenario with large mass difference, Phys. Rev. A 95, 062708, or see our full list of publications

Publications by the Mixtures project

2019Manuel Gerken, Binh Tran, Stephan Häfner, Eberhard Tiemann, Bing Zhu, Matthias Weidemüller, Observation of dipolar splittings in high-resolution atom-loss spectroscopy of 6Li p-wave Feshbach resonances, Phys. Rev. A (Rapid Comm.) 100, 050701 (2019) [pdf]

Bing Zhu, Stephan Häfner, Binh Tran, Manuel Gerken, Juris Ulmanis, Eberhard Tiemann, Matthias Weidemüller, High partial-wave Feshbach resonances in an ultracold 6Li-133Cs mixture, arXiv:1912.01264 (2019)

Bing Zhu, Stephan Häfner, Binh Tran, Manuel Gerken, Juris Ulmanis, Eberhard Tiemann, Matthias Weidemüller, Spin-rotation coupling in p-wave Feshbach resonances, arXiv:1910.12011 (2019)

2017 S. Häfner, J. Ulmanis, E. D. Kuhnle, Yujun Wang, Chris H. Greene, M. Weidemüller, Role of the intraspecies scattering length in the Efimov scenario with large mass difference, Phys. Rev. A 95, 062708 (2017) [pdf]

J. Ulmanis, Heteronuclear Efimov Scenario in Ultracold Quantum Gases, Springer Theses (2017)

2016 J. Ulmanis, S. Häfner, E. D. Kuhnle, M. Weidemüller, Heteronuclear Efimov resonances in ultracold quantum gases, National Science Review 3, 174 (2016) [pdf]

J. Ulmanis, S. Häfner, R. Pires, E. D. Kuhnle, Yujun Wang, Chris H. Greene, M. Weidemüller, Heteronuclear Efimov scenario with positive intraspecies scattering length, Phys. Rev. Lett. 117, 153201 (2016) [pdf]

J. Ulmanis, S. Häfner, R. Pires, F. Werner, D. S. Petrov, E. D. Kuhnle, M. Weidemüller, Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture, Phys. Rev. A 93, 022707 (2016) [pdf]

2015 J. Ulmanis, S. Häfner, R. Pires, E. D. Kuhnle, M. Weidemüller, E. Tiemann, Universality of weakly bound dimers and Efimov trimers close to Li - Cs Feshbach resonances, New J. Phys. 17, 055009 (2015)

2014 R. Pires, J. Ulmanis, S. Häfner, M. Repp, A. Arias, E.D. Kuhnle, M. Weidemüller, Observation of Efimov Resonances in a Mixture with Extreme Mass Imbalance, Phys. Rev. Lett. 112, 250404 (2014) [pdf]

R. Pires, M. Repp, J. Ulmanis, E. D. Kuhnle M., Weidemüller, T. G. Tiecke, C. H. Greene, B. P. Ruzic, J. L. Bohn, E. Tiemann, Analyzing Feshbach resonances: A 6Li-133Cs case study, Phys. Rev. A 90, 012710 (2014) [pdf]

2013 M. Repp, R. Pires, J. Ulmanis, R. Heck, E. D. Kuhnle, M. Weidemüller, E. Tiemann, Observation of interspecies 6Li-133Cs Feshbach resonances, Phys. Rev. A 87, 010701 (2013) [pdf]

2012 J. Ulmanis, J. Deiglmayr, M. Repp, R. Wester, M. Weidemüller, Ultracold Molecules Formed by Photoassociation: Heteronuclear Dimers, Inelastic Collisions, and Interactions with Ultrashort Laser Pulses, Chemical Reviews 112, 4890 (2012)

2011 J. Deiglmayr, M. Repp, O. Dulieu, R. Wester, M. Weidemüller, Population redistribution in optically trapped polar molecules, Eur. Phys. J. D 65, 99 (2011)

J. Deiglmayr, M. Repp, R. Wester, O. Dulieu, M. Weidemüller, Inelastic collisions of ultracold polar LiCs molecules with caesium atoms in an optical dipole trap, Phys. Chem. Chem. Phys. 13, 19101 (2011)

2010 J. Deiglmayr, A. Grochola, M. Repp, O. Dulieu, R Wester, M Weidemüller, Permanent dipole moment of LiCs in the ground state, Phys. Rev. A 82, 032503 (2010)

2009 A. Grochola, A. Pashov, J. Deiglmayr, M. Repp, E. Tiemann, R. Wester, M. Weidemüller, Photoassociation spectroscopy of the B1Π state of LiCs, The Journal of Chemical Physics 131, 054304 (2009)

J. Deiglmayr, M. Repp, A. Grochola, K. Mörtlbauer, C. Glück, J. Lange, O. Dulieu, R. Wester, M. Weidemüller, Formation of ultracold dipolar molecules in the lowest vibrational levels by photoassociation, Faraday Discussions 142, 335 (2009)

J. Deiglmayr, P. Pellegrini, A. Grochola, M. Repp, R. Cote, O. Dulieu, R. Wester, M. Weidemüller, Influence of a Feshbach resonance on the photoassociation of LiCs, New Journal of Physics 11, 055034 (2009)

2008 J. Deiglmayr, A. Grochola, M. Repp, K. Mörtlbauer, C. Glück, J. Lange, O. Dulieu, R. Wester, M. Weidemüller, Formation of ultracold polar molecules in the rovibrational ground state, Phys. Rev. Lett. 101, 133004 (2008)

J. Deiglmayr, M. Aymar, R. Wester, M. Weidemüller, O. Dulieu, Calculations of static dipole polarizabilities of alkali dimers. Prospects for alignment of ultracold molecules, J. Chem. Phys. 129, 064309 (2008)

2007 S. D. Kraft, J. Mikosch, P. Staanum, J. Deiglmayr, J. Lange, A. Fioretti, R. Wester, M. Weidemüller, A high resolution time-of-flight mass spectrometer for the detection of ultracold molecules, Appl. Phys. B, 89, 453 (2007)

2006 Peter Staanum, Stephan D. Kraft, Jörg Lange, Roland Wester, Matthias Weidemüller, Experimental investigation of ultracold atom-molecule collisions, Phys. Rev. Lett. 96, 023201 (2006)

Stephan D. Kraft, Peter Staanum, Jörg Lage, Leif Vogel, Roland Wester, Matthias Weidemüller, Formation of ultracold LiCs molecules, J. Phys. B 39, S993 (2006)

2005 S. D. Kraft, M. Mudrich, M. U. Staudt, J. Lange, O. Dulieu, R. Wester, M. Weidemüller, Saturation of Cs2 photoassociation in an optical dipole trap, Phys. Rev. A 71, 013417 (2005)

2004 M. Mudrich, O. Bünermann, F. Stienkemeier, O. Dulieu, M. Weidemüller, Formation of cold bialkali dimers on helium nanodroplets, Eur. J. Phys. D 31, 291 (2004)

M. Mudrich, S. D. Kraft, J. Lange, A. Mosk, M. Weidemüller, E. Tiesinga, Hyperfine-changing collisions in an optically trapped gas of ultracold cesium and lithium, Phys. Rev. A 70, 062712 (2004)

O. Bünermann, M. Mudrich, M. Weidemüller, F. Stienkemeier, Spectroscopy of Cs attached to helium nanodroplets, J. Chem. Phys. 121, 8880 (2004)

R. Wester, S. D. Kraft, M. Mudrich, M. Staudt, J. Lange, N. Vanhaecke, O. Dulieu, M. Weidemüller, Photoassociation inside an optical dipole trap: absolute rate coefficients and Franck-Condon factors, Appl. Phys. B 79, 993 (2004)

2003 M. Mudrich, S. Kraft, K. Singer, A. Mosk, M. Weidemüller, Thermodynamics in an ultracold mixture of optically trapped atomic gases, in: Interactions in Ultracold Gases: From Atoms to Molecules (2003)

2002 Mudrich, M., Kraft, S., Singer, K., Grimm, R., Mosk, A., Weidemüller, M., Sympathetic Cooling with Two Atomic Species in an Optical Trap, Phys. Rev. Lett. 88, 253001 (2002)

2000 Engler, H., Weber, T., Mudrich, M., Grimm, R., Weidemüller, M., Very long storage times and evaporative cooling of cesium atoms in a quasielectrostatic dipole trap, Phys. Rev. A 62, 031402 (2000)

1999 U. Schünemann, H. Engler, R. Grimm, M. Weidemüller, M. Zielonkowski, Simple scheme for tunable frequency offset locking of two lasers, Review of Scientific Instruments 70, 242-243 (1999)

U. Schlöder, H. Engler, U. Schünemann, R. Grimm, M. Weidemüller, Cold inelastic collisions between lithium and cesium in a two-species magneto-optical trap, The European Physical Journal D 7, 331-340 (1999)

1998 U. Schünemann, H. Engler, M. Zielonkowski, M. Weidemüller, R. Grimm, Magneto-optic trapping of lithium using semiconductor lasers, Optics Communications 158, 263 - 272 (1998)