The Mixtures experiment, under the co-supervision of Prof. Matthias Weidemüller and Prof. Lauriane Chomaz (Quantum Fluids Group), investigates fundamental paradigms of quantum few- and many-body physics. We tune interactions and quantum statistics in ultracold gases of Lithium (fermionic) and Cesium (bosonic) atoms and study a myriad of fascinating effects in strongly interacting quantum matter under extreme control, including Bose-Einstein condensates, degenerate Fermi gases, and mixtures of both in different regimes of quantum degeneracy.
Polaron physics
The problem of the coupling of an impurity to a surrounding quantum bath lies at the heart of a large variety of quantum many-body phenomena. A degenerate ultracold mixture of Li and Cs atoms gives access to both physically relevant limits of light impurities coupled to a Bose-Einstein condensate and of heavy particles to a degenerate Fermi sea, non-trivial paradigms of many-body systems. Our experimental investigations are based on spectroscopic measurements performed on the minority species in regimes where it is strongly interacting with the quantum bath. We are interested, on one hand, in the role played by the mass of the impurity in the dynamics of the many-body system and on the other hand, in the role played by quantum bath as a mediator of interactions between impurities.
status: ongoing project
Efimov physics
The Efimov effect concerns the bizarre property of the quantum three-body problem for which three particles can be bound even if the two-body system is unbound. The ratio between two subsequent trimer energies follows a discrete scale invariance with a universal scaling factor that depends only on the constituent atoms, their mass ratio, and in the number of resonant interactions. Due to the largest mass ratio among stable alkali atoms, our mixture shows a very small Efimov scaling factor favorable for observing heteronuclear Efimov resonances in ultracold gases through magnetic field-dependent loss-spectroscopy. We have experimentally studied three-body recombination and the effects of Efimov trimers close to Li-Cs Feshbach-resonances revealing universal and non-universal aspects.
status: past project
Feshbach resonances
We investigate the quantum statistical properties of Li-Cs mixtures by controlling the inter-species interaction strength employing the unique richness of their Feshbach resonances. At sub-micro-Kelvin temperatures, through the application of a uniform external magnetic field, one can control the collisional properties of the gas and make the effective strength of two-body interaction either attractive or repulsive, arbitrarily large or small. By employing magnetic field-dependent atom-loss spectroscopy we observed several interspecies Fenshbach resonances in the Li-Cs mixture. We attributed the resonances to s-, p- and d-wave molecular channels by a coupled-channels calculation, leading to an accurate determination of Li-Cs ground-state potentials.
status: past project
The Mixtures Team
Prof. Dr. Matthias Weidemüller
Group Leader
Phone: 19470
Prof. Dr. Lauriane Chomaz
Group Leader
Phone: 19496
Tobias Krom
Mixtures
PhD Student
Phone: 19480
Michael Rautenberg
Mixtures
PhD Student
Phone: 19480
Eleonora Lippi
Mixtures
PhD Student
Phone: 19480
Kilian Welz
Mixtures
Master Student
Phone: 19480
Former PhD Students
Former Master Students
| | | |
| Imaging of ultracold Cesium atoms at high magnetic fields | | |
| Theoretical considerations concerning the relation of the Efimov scenario to Fermi polarons and upgrade of a polaron experiment | | |
| Design of a two-dimensional magneto-optical trap for lithium-6 atoms | | |
| Efficient creation of a molecular Bose-Einstein condensate of Lithium-6 using a spatially modulated dipole trap | | |
| Towards Ultracold Lithium-Caesium Ground State Molecules | | |
| Design and construction an optical Microtrap to study the Polaron scenario in an ultracold 6Li -133Cs mixture | | |
| A tunable optical dipole trap for 6Li and 133Cs | | |
| All-Optical Formation of an Ultracold Gas of Fermionic Lithium Close to Quantum Degeneracy | | |
| Gray Molasses Cooling of Lithium-6 Towards a Degenerate Fermi Gas | | |
| Implementation of a movable optical microtrap for mixing ultracold 6Li and 133Cs towards studying the polaron scenario | | |
| Improved manipulation and detection of an ultracold 6Li-133Cs mixture towards the investigationof the Bose polaron | | |
| A reservoir optical dipole trap for creating a Bose-Einstein condensate of 133Cs | | |
| | | |
News from the Mixtures lab
- “An Experimental Platform for Studying the Heteronuclear Efimov Effect with an Ultracold Mixture of Li-6 and Cs-133 Atoms” now published on Few-Body Systems!
Our paper describing the Li-Cs mixing experimental apparatus has been now published in the journal Few-Body Systems! Experiments involving atomic mixtures with a large mass imbalance face significant challenges in slowing, cooling, and trapping the species together. This paper highlights the development of efficient techniques to address these issues, focusing on three aspects: slowing of hot atoms, managing of dipole traps, and controlling magnetic fields. This machine allowed the investigation of the heteronuclear Efimov effect in the ultracold Li-Cs mixture as reported in several previous publications. Reference: Check it out here: An Experimental Platform for Studying the HeteronuclearEfimov Effect with …
- Congratulations to Dr. Lippi!
Congratulations to Eleonora Lippi who today defended her PhD thesis “Cs-133 atoms in a Li-6 Fermi sea for exploring polaron physics in the heavy impurity limit”. It has been a wonderful experience working alongside you and we cannot wait to see what the future brings. We wish you the best of luck! Reference: PhD Thesis: Cs-133 atoms in a Li-6 Fermi sea for exploring polaron physics in the heavy impurity limit
- “Anomalous loss behavior in a single-component Fermi gas close to a p-wave Feshbach resonance” published in Phys. Rev. A !
This month, our paper on “Anomalous loss behavior in a single-component Fermi gas close to a p-wave Feshbach resonance” was published in Phys. Rev. A! In this work we studied the theoretical processes of three-body loss in a p-wave interacting Fermi gas. The study predicts a new type of three-body loss behavior in these kinds of systems which could be observed in lithium-6 polarized in the lowest hyperfine groundstate. Reference:
- Mixtures lab plays as “actor” in the video for promoting Isoquant
The Mixtures lab appears in the video for promoting Isoquant CRC 1225. Check the video on YouTube! This image video was realized within the Isoquant – Science Communication project in collaboration with the scientific film agency Aha! Film. The aim is to explain the spirit of our Collaborative Research Center to a broad audience.
Recent Publications
2023
Welz K, Gerken M, Zhu B, Lippi E, Rautenberg M, Chomaz L, Weidemüller M
Anomalous loss behavior in a single-component Fermi gas close to a p-wave Feshbach resonance Journal Article
In: Phys. Rev. A, vol. 107, iss. 5, pp. 053310, 2023.
@article{PhysRevA.107.053310,
title = {Anomalous loss behavior in a single-component Fermi gas close to a p-wave Feshbach resonance},
author = {K. Welz and M. Gerken and B. Zhu and E. Lippi and M. Rautenberg and L. Chomaz and M. Weidemüller},
url = {https://link.aps.org/doi/10.1103/PhysRevA.107.053310},
doi = {10.1103/PhysRevA.107.053310},
year = {2023},
date = {2023-05-01},
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2022
Tran B
From Efimov Physics to Polarons in an Ultracold Mixture of Li and Cs Atoms PhD Thesis
2022.
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title = {From Efimov Physics to Polarons in an Ultracold Mixture of Li and Cs Atoms},
author = {Binh Tran},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/31882/, heiDOK},
year = {2022},
date = {2022-06-30},
abstract = {This thesis reports on the reconstruction and improvement of a quantum gas experiment for studying Bose polarons as well as on theoretical investigations at the interface between Efimov physics and Fermi polarons. In both experiment and theory an ultracold mixture of fermionic 6Li and bosonic 133Cs with a large mass ratio is considered. With the improved experimental setup we realize Bose-Einstein condensates (BEC) of 133Cs with N = 10^4 atoms and molecular BECs of 6Li2 with N = 10^5 dimers. For the creation of Bose polarons we trap a small number of Li atoms in a tightly confined optical dipole trap and propose a scheme to combine them with the 133Cs BEC. In a theoretical study, employing the Born-Oppenheimer approximation, we calculate Efimov bound state energies (E < 0) in a three body Cs-Cs-Li system and in a many-body environment where two 133Cs atoms are immersed in a Fermi sea of 6Li atoms. In these systems the intraspecies scattering length determine the ground state and the Fermi sea leads to a modification of the binding energies. For the scattering states (E > 0) we calculate the induced scattering length between two 133Cs atoms mediated by the Fermi sea, and find resonant behavior. We find that for large mass ratios bound states can persist at positive energies to form quasibound states.},
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This thesis reports on the reconstruction and improvement of a quantum gas experiment for studying Bose polarons as well as on theoretical investigations at the interface between Efimov physics and Fermi polarons. In both experiment and theory an ultracold mixture of fermionic 6Li and bosonic 133Cs with a large mass ratio is considered. With the improved experimental setup we realize Bose-Einstein condensates (BEC) of 133Cs with N = 10^4 atoms and molecular BECs of 6Li2 with N = 10^5 dimers. For the creation of Bose polarons we trap a small number of Li atoms in a tightly confined optical dipole trap and propose a scheme to combine them with the 133Cs BEC. In a theoretical study, employing the Born-Oppenheimer approximation, we calculate Efimov bound state energies (E < 0) in a three body Cs-Cs-Li system and in a many-body environment where two 133Cs atoms are immersed in a Fermi sea of 6Li atoms. In these systems the intraspecies scattering length determine the ground state and the Fermi sea leads to a modification of the binding energies. For the scattering states (E > 0) we calculate the induced scattering length between two 133Cs atoms mediated by the Fermi sea, and find resonant behavior. We find that for large mass ratios bound states can persist at positive energies to form quasibound states.
Gerken M
Exploring p-wave Feshbach Resonances in Ultracold Lithium and Lithium-Cesium Mixtures PhD Thesis
2022.
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title = {Exploring p-wave Feshbach Resonances in Ultracold Lithium and Lithium-Cesium Mixtures},
author = {Manuel Gerken},
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year = {2022},
date = {2022-05-18},
abstract = {This thesis reports on the exploration of p-wave Feshbach resonances in ultracold Li-6 and Li-6-Cs-133 gases where the pair rotation angular momentum is l=1. An improved experimental apparatus is presented, allowing atom loss spectroscopy with a magnetic field resolutions down to several milli-Gauss on three Li-6, and five Li-6-Cs-133 Feshbach resonances. A doublet structure is observed for the first time on three Li-6 p-wave Feshbach resonances. We assign the splittings to spin-spin interactions where the projection of the pair rotation angular momentum m_l splits the resonance into m_l=0 and |m_l|=1. For the first time we report on observation of spin-rotation interaction on three Li-6-Cs-133 p-wave Feshbach resonances. Here the pair-rotation couples to the atomic spins, leading to an additional splitting of the m_l=-1 and m_l=+1 projections. Via coupled channel calculations we determine the dimensionless spin rotation constant to be |gamma|=0.566(50)x10^(-3). With a simple model we show that the strength of spin-rotation coupling depends significantly on the short-range part of the electron wave functions, highlighting the potential of Feshbach resonances to provide precise information on electron and nuclear wave functions at short internuclear distance. In an additional exploratory study of losses close to a single component Fermi pwave, Feshbach resonance we find changes in qualitative loss behavior depending on the density and temperature of the gas. We separate two regimes depending on the dominance of either elastic or inelastic collisions showing three- or two-body loss behavior, respectively. Collisional losses with possible cooling efficiencies similar to classic evaporative cooling are predicted.},
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This thesis reports on the exploration of p-wave Feshbach resonances in ultracold Li-6 and Li-6-Cs-133 gases where the pair rotation angular momentum is l=1. An improved experimental apparatus is presented, allowing atom loss spectroscopy with a magnetic field resolutions down to several milli-Gauss on three Li-6, and five Li-6-Cs-133 Feshbach resonances. A doublet structure is observed for the first time on three Li-6 p-wave Feshbach resonances. We assign the splittings to spin-spin interactions where the projection of the pair rotation angular momentum m_l splits the resonance into m_l=0 and |m_l|=1. For the first time we report on observation of spin-rotation interaction on three Li-6-Cs-133 p-wave Feshbach resonances. Here the pair-rotation couples to the atomic spins, leading to an additional splitting of the m_l=-1 and m_l=+1 projections. Via coupled channel calculations we determine the dimensionless spin rotation constant to be |gamma|=0.566(50)x10^(-3). With a simple model we show that the strength of spin-rotation coupling depends significantly on the short-range part of the electron wave functions, highlighting the potential of Feshbach resonances to provide precise information on electron and nuclear wave functions at short internuclear distance. In an additional exploratory study of losses close to a single component Fermi pwave, Feshbach resonance we find changes in qualitative loss behavior depending on the density and temperature of the gas. We separate two regimes depending on the dominance of either elastic or inelastic collisions showing three- or two-body loss behavior, respectively. Collisional losses with possible cooling efficiencies similar to classic evaporative cooling are predicted.
2021
Tran B, Rautenberg M, Gerken M, Lippi E, Zhu B, Ulmanis J, Drescher M, Salmhofer M, Enss T, Weidemüller M
Fermions meet two bosons -- the heteronuclear Efimov effect revisited Journal Article
In: Braz. J. Phys., vol. 51, pp. 316, 2021.
@article{tran2020fermions,
title = {Fermions meet two bosons -- the heteronuclear Efimov effect revisited},
author = {Binh Tran and Michael Rautenberg and Manuel Gerken and Eleonora Lippi and Bing Zhu and Juris Ulmanis and Moritz Drescher and Manfred Salmhofer and Tilman Enss and Matthias Weidemüller},
url = {https://doi.org/10.1007/s13538-020-00811-5},
doi = {10.1007/s13538-020-00811-5},
year = {2021},
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2020
Enss T, Tran B, Rautenberg M, Gerken M, Lippi E, Drescher M, Zhu B, Weidemüller M, Salmhofer M
Scattering of two heavy Fermi polarons: resonances and quasi-bound states Journal Article
In: Phys. Rev. A, vol. 102, pp. 063321, 2020.
@article{enss2020,
title = {Scattering of two heavy Fermi polarons: resonances and quasi-bound states},
author = {Tilman Enss and Binh Tran and Michael Rautenberg and Manuel Gerken and Eleonora Lippi and Moritz Drescher and Bing Zhu and Matthias Weidemüller and Manfred Salmhofer},
url = {https://doi.org/10.1103/PhysRevA.102.063321},
doi = {10.1103/PhysRevA.102.063321},
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Grimshandl D, Gerken M, Lippi E, Tran B, Hassan S Z, Becher J H, Jochim S, Weidemüller M, Föhner G, Brucker S, Schumacher F, Beldermann W, Angelov V, Hetzel S, Hummel S, Muley S, Windelband B, Eisner C, Zugaj M, Bayer P, Ernst D, Gehrlein M, Jacob H, Pfeifle J, Treskatsch A, Ulmschneider M, Preiss P M
The HDvent Emergency Ventilator System Working paper
arXiv e-prints: 2012.13005, 2020.
@workingpaper{grimshandl2020hdvent,
title = {The HDvent Emergency Ventilator System},
author = {David Grimshandl and Manuel Gerken and Eleonora Lippi and Binh Tran and Saba Zia Hassan and Jan Hendrik Becher and Selim Jochim and Matthias Weidemüller and Gunnar Föhner and Steffen Brucker and Frank Schumacher and Wolfgang Beldermann and Venelin Angelov and Stefan Hetzel and Stefan Hummel and Simon Muley and Bernd Windelband and Christoph Eisner and Marco Zugaj and Philipp Bayer and Dario Ernst and Marcel Gehrlein and Helmut Jacob and Jens Pfeifle and Andreas Treskatsch and Martin Ulmschneider and Philipp M. Preiss},
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2019
Gerken M, Tran B, Häfner S, Tiemann E, Zhu B, Weidemüller M
Observation of dipolar splittings in high-resolution atom-loss spectroscopy of $^6$Li $p$-wave Feshbach resonances Journal Article
In: Phys. Rev. A (Rapid Comm.), vol. 100, iss. 5, pp. 050701, 2019.
@article{gerken2019,
title = {Observation of dipolar splittings in high-resolution atom-loss spectroscopy of $^6$Li $p$-wave Feshbach resonances},
author = {Manuel Gerken and Binh Tran and Stephan Häfner and Eberhard Tiemann and Bing Zhu and Matthias Weidemüller},
url = {https://link.aps.org/doi/10.1103/PhysRevA.100.050701},
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Zhu B, Häfner S, Tran B, Gerken M, Ulmanis J, Tiemann E, Weidemüller M
High partial-wave Feshbach resonances in an ultracold $^6$Li-$^133$Cs mixture Working paper
arXiv e-prints: 1912.01264, 2019.
@workingpaper{zhu2019,
title = {High partial-wave Feshbach resonances in an ultracold $^6$Li-$^133$Cs mixture},
author = {Bing Zhu and Stephan Häfner and Binh Tran and Manuel Gerken and Juris Ulmanis and Eberhard Tiemann and Matthias Weidemüller},
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Zhu B, Häfner S, Tran B, Gerken M, Ulmanis J, Tiemann E, Weidemüller M
Spin-rotation coupling in p-wave Feshbach resonances Working paper
arXiv e-prints: 1910.12011, 2019.
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title = {Spin-rotation coupling in p-wave Feshbach resonances},
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2017
Häfner S, Ulmanis J, Kuhnle E D, Wang Y, Greene C H, Weidemüller M
Role of the intraspecies scattering length in the Efimov scenario with large mass difference Journal Article
In: Phys. Rev. A, vol. 95, iss. 6, pp. 062708, 2017.
@article{Haefner2017,
title = {Role of the intraspecies scattering length in the Efimov scenario with large mass difference},
author = {S. Häfner and J. Ulmanis and E. D. Kuhnle and Yujun Wang and Chris H. Greene and M. Weidemüller},
url = {http://link.aps.org/doi/10.1103/PhysRevA.95.062708},
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year = {2017},
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Ulmanis J
Heteronuclear Efimov Scenario in Ultracold Quantum Gases Journal Article
In: Springer Theses, 2017.
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title = {Heteronuclear Efimov Scenario in Ultracold Quantum Gases},
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2016
Ulmanis J, Häfner S, Pires R, Kuhnle E D, Wang Y, Greene C H, Weidemüller M
Heteronuclear Efimov scenario with positive intraspecies scattering length Journal Article
In: Phys. Rev. Lett., vol. 117, pp. 153201, 2016.
@article{Ulmanis2016b,
title = {Heteronuclear Efimov scenario with positive intraspecies scattering length},
author = {J. Ulmanis and S. Häfner and R. Pires and E. D. Kuhnle and Yujun Wang and Chris H. Greene and M. Weidemüller},
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Ulmanis J, Häfner S, Kuhnle E D, Weidemüller M
Heteronuclear Efimov resonances in ultracold quantum gases Journal Article
In: National Science Review, vol. 3, pp. 174, 2016.
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title = {Heteronuclear Efimov resonances in ultracold quantum gases},
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Ulmanis J, Häfner S, Pires R, Werner F, Petrov D S, Kuhnle E D, Weidemüller M
Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture Journal Article
In: Phys. Rev. A, vol. 93, iss. 2, pp. 022707, 2016.
@article{Ulmanis2016,
title = {Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture},
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2015
Ulmanis J, Häfner S, Pires R, Kuhnle E D, Weidemüller M, Tiemann E
Universality of weakly bound dimers and Efimov trimers close to Li - Cs Feshbach resonances Journal Article
In: New J. Phys., vol. 17, iss. 5, pp. 055009, 2015.
@article{Ulmanis2015,
title = {Universality of weakly bound dimers and Efimov trimers close to Li - Cs Feshbach resonances},
author = {J. Ulmanis and S. Häfner and R. Pires and E. D. Kuhnle and M. Weidemüller and E. Tiemann},
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