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

Scattering of two heavy Fermi polarons - resonances and quasibound states: paper published in PRA17.12.2020
Eleonora Lippi

Our paper on the " Scattering of two heavy Fermi polarons: Resonances and quasibound states” got published this month in PRA! We theoretically investigate the scattering properties and compute the scattering phase shifts and scattering lengths between two heavy impurities in an ideal Fermi gas at zero temperature. We find that impurities strongly and attractively interacting with the medium exhibit resonances in the induced scattering with a sign change of the induced scattering length and even strong repulsion.

Reference:
T. Enss et al., Scattering of two heavy Fermi polarons: Resonances and quasibound states , PhysRevA, 102.063321 (2020) , or see our full list of publications
Fermions Meet Two Bosons - the Heteronuclear Efimov Effect Revisited: paper published in Braz. J. Phys.09.11.2020
Eleonora Lippi

Our paper on the "Fermions Meet Two Bosons—the Heteronuclear Efimov Effect Revisited" got published in Braz. J. Phys., in a special issue for Prof. Mahir S. Hussein! In this paper we theoretically investigate two limiting cases of the Efimov scenario, first, in vacuum, and second, in the presence of a Fermi Sea, focusing on the specific case of two heavy bosons and a light fermion. While the first case reproduces the well-known features of the Efimov effect, the second case provides novel insights serving as a precursor to understand effective interactions of Fermi polarons, i.e., strongly correlated impurities in a Fermi sea.

Reference:
B. Tran et al., Fermions Meet Two Bosons—the Heteronuclear Efimov Effect Revisited, Braz. J. Phys. (2020), https://doi.org/10.1007/s13538-020-00811-5, or see our full list of publications
Successful second funding period bid of IsoQuant (CRC 1225) 01.06.2020
Eleonora Lippi

Our collaborative research centre (CRC 1225) studying “Isolated Quantum Systems and Universality in Extreme Conditions” has been granted and will continue its work in the second funding period, from July 2020 to 2024! Our group will continue to participate in the collaboration to the project A05 “Dynamics of tunable disordered many-body spin systems” and C03 “Fermi-Bose mixtures with large mass ratio”. Congratulation to everybody!

For more information:
Website: IsoQuant (CRC1225)


Publications by the Mixtures project

2020Binh Tran, Michael Rautenberg, Manuel Gerken, Eleonora Lippi, Bing Zhu, Juris Ulmanis, Moritz Drescher, Manfred Salmhofer, Tilman Enss, Matthias Weidemüller, Fermions meet two bosons - the heteronuclear Efimov effect revisited, Braz. J. Phys. (2020)

Tilman Enss, Binh Tran, Michael Rautenberg, Manuel Gerken, Eleonora Lippi, Moritz Drescher, Bing Zhu, Matthias Weidemüller, Manfred Salmhofer, Scattering of two heavy Fermi polarons: resonances and quasi-bound states, Phys. Rev. A 102, 063321 (2020)

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. a 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 a, M. Weidemüller, Ultracold Molecules Formed by Photoassociation: Heteronuclear Dimers, a 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 a atoms in an optical dipole trap, Phys. Chem. Chem. Phys. 13, 19101 (2011)

2010 J. Deiglmayr, A. Grochola, M. Repp, O. Dulieu, R Wester a, 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 a, 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, a C. Glück, J. Lange, O. Dulieu, R. Wester, M. Weidemüller, Formation of ultracold dipolar molecules in the lowest vibrational a levels by photoassociation, Faraday Discussions 142, 335 (2009)

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

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

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

2006 Peter Staanum, Stephan D. Kraft, Jörg Lange, Roland a 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 a, 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 a, 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 a, 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 a, E. Tiesinga, Hyperfine-changing collisions in an optically trapped gas of ultracold a 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 a, N. Vanhaecke, O. Dulieu, M. Weidemüller, Photoassociation inside an optical dipole trap: absolute rate coefficients a 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 a gases, in: Interactions in Ultracold Gases: From Atoms to Molecules (2003)

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

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

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

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