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 manybody 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 quantumstate sensitive diagnostics.
Latest news from the lab
Universality of weakly bound dimers and Efimov trimers close to Li–Cs Feshbach resonances published in New J. Phys.  14.05.2015 
Eva 
We study the interspecies scattering properties of ultracold LiCs mixtures in their two energetically lowest spin channels in the magnetic field range between 800 G and 1000 G. Close to two broad Feshbach resonances we create weakly bound LiCs dimers by radiofrequency association and measure the dependence of the binding energy on the external magnetic field strength. Based on the binding energies
and complementary atom loss spectroscopy of three other LiCs swave Feshbach resonances we construct precise molecular singlet and triplet electronic ground state potentials using a coupledchannels calculation. We extract the LiCs interspecies
scattering length as a function of the external field and obtain almost a tenfold improvement in the precision of the values for the pole positions and widths of the swave LiCs Feshbach resonances as compared to our previous work [Pires et al., Phys.
Rev. Lett. 112, 250404 (2014)]. We discuss implications on the Efimov scenario and the universal geometric scaling for LiCsCs trimers.

Reference: J. Ulmanis et al., Universality of weakly bound dimers and Efimov trimers close to Li–Cs Feshbach resonances, New J. Phys. 17, 055009 (2015), or see our full list of publications

Analyzing Feshbach resonances: A LiCs case study published in Physical Review A  01.08.2014 
Rico 
We comprehensively compare three different models for the description of Feshbach resonances: The coupledchannel calculation, the asymptotic bound state model (ABM), and the multichannel quantum defect theory (MQDT). All models describe our previously measured LiCs Feshbach resonances accurately. This work demonstrates on the example of LiCs, how measured Feshbach resonances can be interpreted by use of simple models.
Since an exact analytical solution of the Schrödinger equation for the collision of two ultracold alkali atoms is not possible, assumptions have to be implemented in order to facilitate the calculation. One model, namely the ABM, which applies such assumptions, did not agree with our experimental findings (see [Repp et al., Phys. Rev. A 87, 010701(R) (2013)]). Spurred by this discrepancy, together with our collaborators we applied and compared three different methods for the calculation of Feshbach resonances. In the course of this analysis the ABM was extended so that it can also correctly describe the scattering behavior of a system where both a virtual and a bound state play a role, as is the case for LiCs. With this analysis we now have a very accurate characterization of the field dependent scattering length, which is required for our study of few and manybody physics.

Reference: R. Pires et al., Analyzing Feshbach resonances: A LiCs case study, Phys. Rev. A 90, 012710 (2014), or see our full list of publications

Rico Pires and Hanna Schempp obtain their PhDs  24.07.2014 
Rico 
This week both Hanna Schempp from the Rydberg team, and Rico Pires from the mixtures team successfully defended their PhD theses: Congratulations!

Reference: R. Pires, Efimov Resonances in an Ultracold Mixture with Extreme Mass Imbalance, PhD thesis H. Schempp, Formation of Aggregates and Energy Transport in Ultracold Rydberg Interacting Gases, PhD thesis, or see our full list of publications

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Research topics
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.
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 stronglycorrelated quantum systems that is highly controllable and completely governed by interatomic interactions.
We are currently setting up this new experiment. Our goal is to investigate multiple electron capture using the combined techniques of magnetooptically cooling and trapping of the target atoms and using recoil ion momentum spectroscopy.
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 ultralow temperatures. In this regime the reaction dynamics are no longer concealed by the thermal movement of the particles.
We are setting up an experiment to study the physics of twoelectron 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 manybody effects induced by the longrange interactions between highly excited strontium Rydberg atoms, using the inner electron to control the atom's motion and to detect single Rydberg atoms.