Our experiments focus on the study of single Rydberg atoms embedded in an ultracold quantum gas at temperatures in the nanokelvin regime. Our ability to control such Rydberg impurities with principal quantum numbers up to n~200 allows us to investigate situations where the size of the Rydberg atom by far extends the typical distance between the trapped atoms. This provides ways to investigate the interaction of the Rydberg electron with single, few, or many neutral perturbers residing within the electronic orbital. The quantum mechanical scattering process describing this interaction leads to a new molecular bond and the formation of giant so-called ultralong-range Rydberg molecules.
For many perturbers within the Rydberg orbit, which is realized when exciting the Rydberg state in a Bose-Einstein condensate, the contribution of higher-order partial waves in the electron-neutral scattering process can be studied. Specifically, a detailed modelling of the excitation lineshape, which is strongly shifted and broadened by the interaction with the condensate, reveals signatures of an electron-atom p-wave scattering resonance. Moreover, the lifetime of the Rydberg electron in the dense medium is determined by chemical reactions on micrometer length scales and microsecond time scales, leading to molecular ion formation and collision-induced changes of the electron’s orbital angular momentum. In this regime, we are currently pursuing to observe the backaction of the Rydberg electron on the condensate density distribution, a mechanism that may lead to a microscopy tool for electronic orbitals.
Very recently, we have focused on the interaction of the positively charged ionic Rydberg core with the Bose-Einstein condensate. This ion-atom interaction is much weaker than the electron-atom interaction and typically fully disguised by the latter. However, the contribution of the electron can be largely reduced once its orbit exceeds the typical size of the atomic sample. At the same time, the presence of the electron serves as a protective Faraday shield for the ion from detrimental electric stray fields. We demonstrate this regime using a micron-sized optical tweezer trap and observe evidence for ion-atom interaction. These experiments may lead to a new way for studying ionic impurities in a BEC at temperatures where quantum effects in the scattering process start to play a role, with prospects for the exploration of associated polaron physics.
In our apparatus, we employ combinations of magnetic and optical trapping and cooling techniques to achieve Bose-Einstein condensation of 87Rb inside an in-chamber electric field control cage, which allows us to create single Rydberg atoms with principal quantum number up to n~200. Rydberg states are conveniently accessed via a two-photon transition with lasers at 420nm and 1020nm, both stabilized to a high-finesse optical cavity for high-resolution Rydberg spectroscopy. Efficient detection of single Rydberg atoms is achieved by means of electric field ionization and ion detection using either a microchannel plate (MCP) or a channeltron.
Additionally, our apparatus hosts an in-vacuum aspheric lens for high-resolution in-situ imaging and addressing of our condensate. This provides means to create localized Rydberg impurities at well defined positions. Apart from spectroscopic studies of the impurity, the apparatus is specifically designed to investigate the effect of the impurity on the condensate density distribution with sub-micrometer optical resolution.
We are always looking for motivated new team members!
We are currently trying to spatially image an electron wave function directly by its interaction with a Rb Bose-Einstein Condensate. For this we are looking for
- a PhD student
If you are interested in our effort to understand the physics of Rydberg atoms in quantum gases , contact F. Meinert, R. Löw, or T. Pfau via email/phone or just come by and visit our labs (5.125).