Physikalisches Institut
Im Neuenheimer Feld 226
69120 Heidelberg
Tel: 06221/ 54 19471
Fax: 06221/ 54 19545
"Phase transitions and avalanches: Studying strongly correlated phenomena in cold Rydberg gases"
Dr. Oliver Morsch
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
Analyzing Feshbach resonances: A LiCs case study published in Physical Review A  01.08.2014 
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 investigation, 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: 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 

Reference: Efimov Resonances in an Ultracold Mixture with Extreme Mass Imbalance , PhD thesis Formation of Aggregates and Energy Transport in Ultracold Rydberg Interacting Gases, PhD thesis, or see our full list of publications 
Observation of Efimov Resonances in a Mixture with Extreme Mass Imbalance published in Phys. Rev. Lett.!  25.06.2014 
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 socalled Feshbach resonance, where the interaction energy between Li and Cs is tunable, we let the atoms interfere with several threebody bound states of the underlying scattering resonance. When the Efimov resonance is hit, the atoms experience an enhanced threebody loss and we record the threebody loss rate by a timeresolved 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.

Reference: 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: 