Ultracold Fermi-Bose mixtures

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

Group Leader

Prof. Dr. Matthias Weidemüller

Group Leader
Phone: 19470

External

Prof. Dr. Lauriane Chomaz

Group Leader
Phone: 19496

Mixtures

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

Name

Thesis Title

Year

Group

Schönhals, Arthur

Imaging of ultracold Cesium atoms at high magnetic fields

2013

Mixtures

Rautenberg, Michael

Theoretical considerations concerning the relation of the Efimov scenario to Fermi polarons and upgrade of a polaron experiment

2021

Mixtures

Noßke, Ingo

Design of a two-dimensional magneto-optical trap for lithium-6 atoms

2013

Mixtures

Neiczer, Markus

Efficient creation of a molecular Bose-Einstein condensate of Lithium-6 using a spatially modulated dipole trap

2018

Mixtures

Matthies, Jonas

Towards Ultracold Lithium-Caesium Ground State Molecules

2018

Mixtures

Klaus, Lauritz

Design and construction an optical Microtrap to study the Polaron scenario
in an ultracold 6Li -133Cs mixture

2019

Mixtures

Häfner, Stephan

A tunable optical dipole trap for 6Li and 133Cs

2013

Mixtures

Heck, Robert

All-Optical Formation of an Ultracold Gas of Fermionic Lithium Close to Quantum Degeneracy

2012

Mixtures

Gerken, Manuel

Gray Molasses Cooling of Lithium-6 Towards a Degenerate Fermi Gas

2016

Mixtures

Freund, Robert

Implementation of a movable optical microtrap for mixing ultracold 6Li and 133Cs towards studying the polaron scenario

2022

Mixtures

Filzinger, Melina

Improved manipulation and detection of an ultracold 6Li-133Cs mixture towards the investigationof the Bose polaron 

2018

Mixtures

Arias, Alda

A reservoir optical dipole trap for creating a Bose-Einstein condensate of 133Cs

2014

Mixtures


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.

Links | BibTeX

2022

Tran B

From Efimov Physics to Polarons in an Ultracold Mixture of Li and Cs Atoms PhD Thesis

2022.

Abstract | Links | BibTeX

Gerken M

Exploring p-wave Feshbach Resonances in Ultracold Lithium and Lithium-Cesium Mixtures PhD Thesis

2022.

Abstract | Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

Ulmanis J

Heteronuclear Efimov Scenario in Ultracold Quantum Gases Journal Article

In: Springer Theses, 2017.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX

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.

Links | BibTeX