Rydberg Atoms in Bose-Einstein Condensates

Rydberg atoms immersed into a condensate of ultracold ground state atoms is a complex many-body problem. We study systematic approaches to this intriguing situation where many different interactions take place.  Different levels of approaches are pursued such as treating the condensate as a classical coherent state or taking into account the quantized excitations of the condensate. Experiments on these systems are under way at several groups.

Rydberg Atoms

Rydberg atoms, in contrast to atoms in their electronic ground states, possess extraordinary properties. They are of  gigantic extension and the highly excited states possess extremely long radiative lifetimes of the order of milliseconds. Pictorially speaking the valence electron of a Rydberg atom is in a large loosely bound orbit. Consequently Rydberg atoms possess  large polarizabilities  and are extremely sensitive to external fields. To take advantage of the susceptibility of Rydberg atoms to external fields, and iin particular to other Rydberg atoms, ultracold Rydberg gases can be created. Starting from laser cooled atomic clouds, the atoms are excited using a laser tuned slightly below the ionization energy. The so created strongly interacting ultracold Rydberg gases are ideal candidates to study intriguing many-body physics and collective quantum phenomena on a macroscopic scale.

Bose-Einstein Condensation

Ever since the experimental realization of Bose-Einstein condensation (awarded with the Nobel prize in 2001; see http://cua.mit.edu/ketterle_group/research.htm for a nice website), ultracold atoms have been an enourmously popular research object. Using the atoms' interaction with electric (Laser) and magnetic fields, one can virtually `design' both their external trapping forces and their interactions. That makes them an extremely useful tool to study all kinds of fundamental physics (such as superconductivity/superfluidity). But there also applications exploiting their coherence: e.g., in atom interferometry or in quantum computation.

Rydberg Atoms immersed in a Bose-Einstein Condensate

The problem we investigate bridges the gap between the situations described above, namely the cases of many Rydberg atoms and that of many ground state atoms:  We explore the spectral structure of a Rydberg atom immersed into a Bose-Einstein condensate. This system is of immediate physical interest and well-accessible within present-days ultracold experimental techniques.
The electronic spectrum of the Rydberg atom depends crucially on characteristic parameters of the condensate and of the quantum numbers of the Rydberg state. Therefore it is possible to determine these parameters of the condensate by spectroscopy of the energy spectrum of a single atom. As an example the dependency of the shift of the energy spectrum due to the interaction with the condensate for the n=30 states on the axial trapping frequency for an axial symmetric harmonic trap is shown.
 

Invitation

You are warmly welcome to join our efforts to uncover natures secrets: please step by (INF 229 (Umweltphysik), 6th floor, room 620) or drop a note (stephan.middelkamp@pci.uni-heidelberg.de).