@Jankunas2014a], which finally has lead to recent observation of scattering resonances in Penning ionization using merged beams [@Narevicius]. It also recently became possible to produce ultracold KRb molecules in optical traps by using Feshbach resonance and the STIRAP technique, high phase space density [@Ospelkaus2010; @Ni2010; @Miranda2011]. A number of different experiments basing on this technique is now being performed with other species, for now mainly consisting of alkali atoms [@Winkler2007; @Hudson2008; @Deiglmayr2011a; @Takekoshi2014]. The electronic, hyperfine, rotational and vibrational state of the produced molecules can be controlled with external fields, so the dependence of chemical reaction rates on the internal state can be analyzed experimentally. Calculations show that many of those molecules can be highly reactive [@Zuchowski2010; @Tomza2013]. Another possibility is to study reactions of cold atoms and ions [@Willitsch2008; @Rellergert2011; @Willitsch2012]. Apart from studying the inelastic collisions, ultracold atoms, ions and molecules offer the opportunity to act as quantum simulators of many-body effects, or to implement quantum information processing protocols [@DeMille2002; @Ortner2009; @Gorshkov2011; @Hazzard2013; @Wall2013].

In the ultracold limit the collision process crucially depends on the quantum statistics, as the scattering of identical fermions exhibits a $p$-wave centrifugal barrier, in contrast to collisions of bosons or distinguishable particles. Quantum 