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

Observation of Efimov Resonances in a Mixture with Extreme Mass Imbalance published in Phys. Rev. Lett.!21.07.2014

We observed universal Efimov trimer states in a mixed quantum gas, where they appear with a universal scaling factor that is different from homogeneous systems and - in our case - is small enough to reveal a series of trimer states.

Vitaly Efimov predicted already 40 years ago that there is a universal law for any three resonantly interacting particles and that this law has a discrete scaling behavior, i.e. that the resonances appear on a regular basis. We started with an ultracold gas of Li and Cs at temperatures as low as 400 nK and held the strongly interacting mixture in an optical dipole trap. By precisely changing the external magnetic field near a so-called Feshbach resonance, where the interaction energy between Li and Cs is tunable, we let the atoms interfere with several three-body bound states of the underlying scattering resonance. When the Efimov resonance is hit, the atoms experience an enhanced three-body loss and we record the three-body loss rate by a time-resolved measurement of the atom number. The scaling factor between resonances depends on the mass ratio, for which we measure a value of 5 from the series of resonances in good agreement with the theoretical prediction. While the ground Efimov state is about 50 nm in size, the 2nd excited Efimov state is very large with a length scale of almost one µm.

R. Pires et al., Observation of Efimov Resonances in a Mixture with Extreme Mass Imbalance, Phys. Rev. Lett. 112, 250404 (2014), or see our full list of publications

For more information:
University press release: www.uni-heidelberg.de/presse/news2014
wired.com: Physicists Prove Surprising Rule of Threes, http://www.wired.com/Rule_of_Threes

Double degeneracy of Li and Cs in the mixtures lab!01.03.2014

We successfully produced quantum degenerate gases of bosonic 133Cs and fermionic 6Li. This allows us to explore new physics in many exciting experiments with mixed quantum gases.

Li is loaded directly after magneto-optical trapping into the crossed dimple trap at 140 W provided by an Yb fiber laser. Forced evaporation at 690 G leads to about 120000 atoms at 230 nK before the laser power is finally ramped down to values between 80 and 230 mW at which the bimodal distribution is visible. After Cs atoms are captured in a magneto-optical trap they are cooled by degenerate Raman side-band cooling into a reservoir trap. Before the final evaporation about 85000 Cs atoms are transferred into the dimple trap and Bose-Einstein condensation is reached for final laser powers between 130 and 150 mW.

German-Japanese Colloquium on Frontiers of Laser Science organised by Humboldt awardee Kenji Ohmori and Matthias Weidemüller16.01.2014

The Japanese Society for the Promotion of Science, in cooperation with the Heidelberg Center for Quantum Dynamics, organized a joint German-Japanese Colloquium on “Frontiers of Laser Science”. The symposium explored recent developments in modern Atomic, Molecular, Optical Physics and Quantum Optics with special emphasis on advances in fundamental science based on the application of lasers. Leading scientists from Japan and Germany presented and discussed their contributions to the field, opening new perspectives for ongoing or prospective scientific collaborations between both countries. The format of the symposium was similar to the 2011 “Round Table on the Basic Natural Science”, also held at the IWH.

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.