29.11.2016 - Piotr Zuchowski - Cold collisions of metastable helium with atoms and molecules

Development of techniques for cooling and manipulating atoms and molecules was very impressive in past several years. One of the important outcomes of this amazing progress was emergence of new experiments on molecular and atomic collisions which provide information on interactions in unprecedented detail.

It is usually believed that quantum chemistry methods are not accurate enough to provide interaction potentials good enough to predict collisional properties in ultracold regime, as the scattering is very sensitive for variation of the potential. I will revise this statement and discuss for what systems we might expect ab-initio methods to be accurate enough to  quantitatively predict such parameters as the scattering lengths.

I will give example of Penning-ionizing systems containing metastable helium (He*) and closed-shell species. I will show how quantum chemistry methods can provide interaction potentials which predict low-energy shape resonances in He*+molecular hydrogen system in recently performed experiments in Narevicius group (Weizmann Institute). I will discuss also other system for which theory provided crucial guidance: the ultracold mixture of metastable helium and rubidium atoms. This system was recently investigated experimentally by the group of Steven Knoop (VU Amsterdam) who determined the termalization rates of the He*+Rb mixture in magnetic trap in which system experiences only the quartet potential. Theoretical calculations predicted very accurately the scattering lengths.

See poster.