Interactions of anions with ultacold atoms in a hybrid trap

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Molecules and molecular ions in the ultracold temperature regime open new perspectives for the investigation of fundamental phenomena such as cold collisions, reactive dynamics or quantum chemistry, and also find a wide range of exciting applications in, e.g., high precision spectroscopy or quantum computation. During the last decade, an increasing number of techniques have been developed for preparing or creating molecular samples in the ultracold temperature regime. Nevertheless, an efficient method for cooling molecular anions into the millikelvin regime is still lacking. The present project aims at the investigation of the interaction dynamics between ultracold atoms and negative molecular ions. Specifically, our main goal is to demonstrate sympathetic cooling of molecular anions in collisions with laser-cooled atoms. We will explore and expand methods to determine motional and internal energy distributions of trapped ions, in particular photodetachment spectroscopy and tomography. We seek to measure rate coefficients of different reactive channels in atom-molecular anion systems for an extended understanding of ultracold reaction dynamics involving negatively charged molecules.The use of a hybrid atom-ion trap (HAITrap) is the ideal experimental platform for achieving this goal since it combines ions stored in an radiofrequency (rf) trap with optically trapped ultracold atoms under highly controllable conditions. We have recently set up a novel HAITrap consisting on an octupole rf linear trap for ions combined with a Dark Spontaneous Force Optical Trap (darkSPOT) for ultracold atoms. Within the framework of this research proposal we will investigate the system OH- + Rb as a prototypical system for understanding elastic and inelastic interactions between molecular anions and ultracold atoms. Due to its fundamental role in inorganic, organic and atmospheric chemistry, the molecular anion OH- is a well-suited test system for studying fundamental questions concerning reaction dynamics. The combined system OH- + Rb appears to be advantageous for sympathetic cooling of the internal and motional degrees of freedom of the molecular anions, which, in principle, should allow preparation in the absolute rotational and vibrational ground state. We will then extend the experiment to more complex polyatomic molecular anions, in particular hydrated water clusters OH-(H2O)n to address the transition from gas to condensed phase environments, and another prototypical molecular anion, SF6-.This project builds upon the well-established collaboration between the two groups at the University of Heidelberg, Germany, and the University of Innsbruck, Austria, repectively, combining their mutually complementary expertise in the physics of ultracold quantum gases, ion trapping and molecular reaction dynamics.