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

New flavor of universal three-body physics discovered10.10.2016

Our recent theory – experiment collaboration between physicists from Purdue, Kansas State and Heidelberg universities has revealed an unexpected universality in the three-body system consisting of two heavy and one light particles. The results for the first time showed that a class of atomic and nuclear few-body systems behaves identically. Since three-body physics is a critical building block towards theories describing strongly interacting many-body systems, these novel findings will be important for further studies of exotic quantum matter in extreme conditions. They will also contribute to the understanding of one of the oldest questions in quantum mechanics, namely, to what extent different physical systems can be described by the same fundamental laws of quantum mechanics.

In our studies we used an ultracold mixture of Li and Cs atoms to investigate the heteronuclear Efimov scenario. In this scenario, three particles, for our system one Li atom and two Cs atoms, bind together in a bound state even though none of the individual pairs can be bound (analogous to Borromean rings). In the experiments and theory we replaced the unbound Cs pair with a bound one. To our surprise, the resulting Efimov scenario was independent of molecular forces that govern chemical binding of atoms into molecules: the binding of the three atoms was purely quantum-mechanical and the three-body system became truly universal. In this regime it would not matter if one used atoms or nucleons with the same mass ratio and interactions. Furthermore, our experiments showed that the Efimov effect itself is severely modified by the same change of the fundamental nature of the Cs-Cs bond.

The peculiar nature of Efimov physics is illustrated in the figure. It shows the probability density distribution of the Li atom in a CsCsLi Efimov molecule. The two red balls along the central symmetry line indicate the two Cs atoms, which are separated by about 8 nm. In comparison, a typical chemist's molecule, such as CsCs, LiCs or LiCsCs, would have a spatial extent smaller than 1 nm, which was roughly the size of the dark spot between the two Cs atoms. Figure courtesy of Yujun Wang, Kansas State University.

J. Ulmanis et al., Heteronuclear Efimov Scenario with Positive Intraspecies Scattering Length, Phys. Rev. Lett. 117, 153201 (2016), or see our full list of publications
Signing ceremony of a Memorandum of Understanding for a Joint German-Sino Institute for Advanced Quantum Science03.10.2016

The University of Heidelberg and the University of Science and Technology of China have signed a Memorandum of Understanding to found a Joint German-Sino Institute for Advanced Quantum Science. The ceremony was witnessed by (left to right on the picture) the Chinese Vice Consul General, Mr. Wei-Ping Xing, the Secretary General of Anhui Province, Mr. Ying-Chun Wang, the Excutive Director of the Hefei National Laboratory for Physical Sciences at the Microscale, Prof. Li Yuo, the Vice Rector of the University of Heidelberg, Prof. Stephen Hashmi, the Representative of the Baden-Württemberg Ministery for Science, Education and the Arts, Ms. Martina Diesing, and the Director of the Heidelberg Center for Quantum Dynamics, Prof. Matthias Weidemüller.

For more information:
The press release of USTC (in Chinese): Memorandum of Understanding signed between China University of Science and Technology and Heidelberg University

Density matrix reconstruction of three-level atoms via Rydberg electromagnetically induced transparency published in J. Phys. B: At., Mol. Opt. Phys.!22.07.2016
Vladislav Gavryusev

The full one-body density matrix of an ultracold gas of three-level atoms under electromagnetically induced transparency conditions can be reconstructed through a combined measurement and analysis of the spatially resolved optical spectrum and of the total excited-atom number.

Our method gives a simple explanation to the counter-intuitive features observed in the spectra and provides the optical susceptibility and the Rydberg density as a function of spatial position, as well as the spatial profile of Rabi frequencies of the coupling laser. These results help elucidate the interplay of matter and light degrees of freedom in three-level media and will facilitate new studies of many-body effects in optically driven Rydberg gases.

V. Gavryusev et al., Density matrix reconstruction of three-level atoms via Rydberg electromagnetically induced transparency, J. Phys. B: At., Mol. Opt. Phys. 49, 164002 (2016), or see our full list of publications
For more highlights see our news page

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.