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

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

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.

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
The PhD work of Juris Ulmanis published in the book series Springer Thesis 10.03.2017

Juris Ulmanis from the mixtures team receives the Springer thesis award for his PhD work. Congratulations!

His thesis explores the Efimov scenario, which is one of the prime examples of how fundamental quantum physics universally transpire across seemingly disparate fields of modern science. Initially speculated for nuclear physics more than 40 years ago, the Efimov effect has become a new research paradigm not only in ultracold atom physics but also in molecular, biological and condensed matter systems. In his work, Juris used a heteronuclear mixture of ultracold Li and Cs atoms to measure the scaling factor, which is a hallmark property and sometimes referred to as the “holy grail” of Efimov physics. These results allowed to pioneer experimental understanding of universal properties that unify the description of different three-body systems, as well as to discern microscopic, non-universal properties that sets different systems apart.

The book features a completely rewritten introduction that is aimed at young scientists just starting in the field of few-body physics. On top of a light primer on the Efimov effect, it highlights aspects of three-body physics in ultracold quantum gases and places these ideas in a wider context touching nuclear, atomic, and molecular physics. The rest of the work closely follows the original thesis.

For more information:
Read the book on Springer Theses

Binh Tran receives Poster Prize at Summer School in São Paulo10.02.2017
Binh Tran

During the "School on Interaction of Light with Cold Atoms" in São Paulo for young students and researchers, Binh Tran from the Mixtures team presented a poster with the title “Towards creating Bose and Fermi Polarons in an ultracold Li-Cs Mixture with a large Mass Ratio” which was selected as the best poster. Congratulations!

For more information:
Website: School on Interaction of Light with Cold Atoms

Publications by the Mixtures project

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)