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

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
Maria Martinez Valado obtains her PhD19.05.2015

Congratulations to Maria Martinez Valado for successfully defending her thesis with title "Investigation of correlations between strongly interacting Rydberg excitations in cold gases using Full Counting Statistics" and for obtaining her PhD degree in a cotutelle between the University of Pisa and the University of Heidelberg.

Universality of weakly bound dimers and Efimov trimers close to Li–Cs Feshbach resonances published in New J. Phys. 14.05.2015

We study the interspecies scattering properties of ultracold Li-Cs 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 radio-frequency 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 Li-Cs s-wave Feshbach resonances we construct precise molecular singlet and triplet electronic ground state potentials using a coupled-channels calculation. We extract the Li-Cs interspecies scattering length as a function of the external field and obtain almost a ten-fold improvement in the precision of the values for the pole positions and widths of the s-wave Li-Cs 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.

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
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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.