Group seminar at MPQ and Zoom: Dynamic processes in Rydberg-atom–ion Systems

Moritz Berngruber, University of Stuttgart, Germany
Group seminar at MPQ lecture hall B 0.32 and Zoom
Thursday, 01 August, 09:00 am (MEZ)

In my talk, I will report on work done during my PhD using an ion microscope to investigate the physics behind ion–Rydberg interactions in real space. The ion microscope setup is able to detect positively charged particles, including atomic and molecular ions, as well as Rydberg state immediately after their ionization. The imaging system reaches a magnification of about 1500 and a resolution of at least 200 nm. This apparatus was used to observe charged Rydberg-atom–ion molecules consisting of an ion and a highly excited Rydberg atom. The molecule is based on a charge-induced flipping dipole bond and shows a bond length of several micrometers, which is well within the resolution of our microscope. Due to the versatile nature of the ion microscope, the molecules could not only be studied by means of traditional spectroscopy and mass spectrometry, but could also directly be observed in real space images.
Thus, the spatial alignment of the two particles, caused by the laser polarization during the photoassociation, could be detected in situ. Furthermore, the response of the molecule to an external electric field was investigated, which opens up the possibility to not only associate the molecule in an aligned way but to directly create orientated molecules. Owing to the exceptionally long bond length of these diatomic molecules, dynamical processes are slowed down drastically. This provides the possibility to observe the vibrational motion of the molecules. Moreover, the onset of the collision dynamics between an ion–Rydberg atom pair in a purely attractive potential was analyzed. At sufficiently small distances, the charge-induced Stark shift leads to a large number of avoided crossings between an atomic Rydberg S-state and the adjacent hydrogenic manifold. These crossings open up additional fast collision channels for a system originally in the Rydberg S-state. For a certain energy regime this results in a counter-intuitive behavior, as initially slow particles predominantly occupy steep collision channels and therefore undergo a fast collisional process compared to initially faster ion-Rydberg pairs that mostly populate slow collision channels.