Quantum dynamics of atomic and molecular systems

Our group studies atomic and molecular quantum systems with respect to their interactions on different levels of complexity. Of special importance is the application and extension of modern methods for the manipulation and quantum control to many-body quantum systems, in particular using coherent light. The systems under investigation range from highly excited Rydberg atoms over atomic and molecular quantum gases to molecular aggregates. The group develops technologies for trapping and cooling of neutral atoms as well as quantum-state sensitive diagnostics.

Latest news from the lab

Tests of universality in the heteronuclear Efimov scenario16.02.2016

We have observed a series of three consecutive Efimov resonances in a three-body recombination spectrum of an ultracold mixture of Li and Cs atoms for the first time. This is an important benchmark for universal zero-range theories, and is considered to be a key ingredient for the fundamental understanding of the transition between few- and many-body physics.

Universal phenomena do not depend on the details of the underlying two-body potential or the type of interaction, and therefore can be found in various areas of modern quantum physics. A prototypical example is the Efimov scenario, where three resonantly interacting particles, be it elementary particles or neutral atoms, can bind into three-body bound states with an energy spectrum that follows an infinite geometrical progression, or in more general terms – the trimers exhibit a discrete scaling symmetry. The analysis of our data, which was performed in close collaboration with colleagues from Paris, France, revealed the existence of such universal scaling. At the same time, strong indications of non-universality due to residual van der Waals interaction could also be observed. This knowledge will be crucial for the further investigation of many-body properties of quantum matter in extreme conditions and could shed light on the structure of very different few-body systems.

J. Ulmanis et al., Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture, Phys. Rev. A 93, 022707 (2016), or see our full list of publications
Juris Ulmanis obtains his PhD28.11.2015

After a sucessfull thesis defense Juris Ulmanis from the Mixtures team obtains his PhD degree. Congratulations!

J. Ulmanis, Universality and non-universality in the heteronuclear Efimov scenario with large mass imbalance, PhD thesis, or see our full list of publications
Three photon off-resonant excitation of Rybderg |nP> states12.06.2015

We can now reliably excite Rydberg atoms in an |nP> state via a three photon off-resonant excitation scheme. This is an important step towards the achievement of single Rydberg atom sensitivity in the Interaction Enhanced Imaging technique that we recently developed and demonstrated. In this method, the interaction between a Rydberg state that we call "impurity" and another one called "probe", coupled via Electromagnetically Induced Transparency (EIT) to the ground state, is leveraged to change the optical properties of the atom cloud, which would be transparent due to EIT, and make it absorptive only in the neighbourhood of the impurity, thus allowing to detect its position. We can now use |nP> states as impurities and |nS> as probing ones to leverage their strong dipole-dipole interactions, which lead to an increase of absorption per each impurity.

The first step of the excitation is done via a circularly polarized 780 nm beam, red detuned by 100 MHz from the ground to excited transition, then a circularly polarized 480 nm laser is used to get 100 MHz below a Rydberg |nS> state. Finally the Rydberg |nP> state is excited by applying a microwave radiation pulse, appropriately tuned to compensate for the detuning of the previous two steps. We apply a small magnetic field to remove the Zeeman degeneracy and to address a well defined Zeeman substate.

G. Günter et al., Observing the Dynamics of Dipole-Mediated Energy Transport by Interaction Enhanced Imaging, Science 342, 954 (2013), or see our full list of publications
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Research topics

Mixtures of ultracold atoms and molecules

In this experiment we use a mixture of two different alkali metals: cesium and lithium. This gives us the possbility to form ultracold LiCs dimers. These molecules have an extremely large electric dipole moment which promises many new experiments. For example, the molecules can be orientated in an external electric field.

Strongly-correlated Rydberg quantum gases

Rydberg atoms are atoms in highly excited electronic states. These atoms are very sensitive to external fields and experience extremely strong interactions with other Rydberg atoms. This gives us a model system for studying strongly-correlated quantum systems that is highly controllable and completely governed by interatomic interactions.

Collisions of highly charged ions and cold atoms

We are currently setting up this new experiment. Our goal is to investigate multiple electron capture using the combined techniques of magneto-optically cooling and trapping of the target atoms and using recoil ion momentum spectroscopy.

Hybrid ion atom trap for cold chemistry experiments

Interactions between ions and neutrals play an important role in all kind of chemical reactions. In order to gain a full understanding of these systems we are trying to observe reactions at ultra-low temperatures. In this regime the reaction dynamics are no longer concealed by the thermal movement of the particles.

Rydberg physics with ultracold two-electron systems

We are setting up an experiment to study the physics of two-electron Rydberg atoms using a quantum gas of ultracold strontium. The experiment is located at the University of Science and Technology of China (USTC Shanghai Institute for Advanced Studies). First studies will be aiming to explore many-body effects induced by the long-range interactions between highly excited strontium Rydberg atoms, using the inner electron to control the atom's motion and to detect single Rydberg atoms.