An ultracold gas of bosonic 23Na39K ground-state molecules
Creators: name: Voges, Kai Konrad
Publisher: name: Hannover : Institutionelles Repositorium der Leibniz Universität Hannover
Year: 2020
Subjects: subject: ultracold molecules
subject: Bose gases
subject: Feshbach resonances
subject: Feshbach molecules
subject: molecular spectroscopy
subject: polar molecules
subject: ultracold collisions
subject: ultracold atoms
subject: ultrakalte Moleküle
subject: Bose-Gase
subject: Feshbachresonanz
subject: Feshbachmoleküle
subject: Molekülspektroskopie
subject: STIRAP
subject: polare Moleküle
subject: ultrakalte Stöße
subject: ultrakalte Atome
subject: Dewey Decimal Classification::500 | Naturwissenschaften::530 | Physik

description: Ultracold bialkali polar molecules play a leading part at the frontline of quantum physics. They recently attract a lot of attention in the ﬁeld of ultracold quantum chemistry, quantum many-body physics and quantum simulations. The key for their success is the rich internal level structure with rotational and vibrational degrees of freedom and their large electric dipole moments. Still, only a handful of molecular species are available at ultracold temperatures until now, although it is highly desirable to produce new molecular species to further expand the range of applications. Besides direct laser cooling methods for molecules, the assembly of heteronuclear ground-state molecules from ultracold atomic mixtures is the most promising approach for the creation of polar molecules. It includes the formation of weakly bound Feshbach molecules from the diatomic mixture and the subsequent two-photon stimulated Raman adiabatic passage (STIRAP) transfer to the rovibrational ground state. This creation strategy has been successfully demonstrated for the ﬁrst time in the pioneering experiments at JILA with ultracold 40K87Rb molecules. Since then, only a few more molecular species from diﬀerent alkali atoms have been created, namely 6Li23Na, 23Na40K, 23Na87Rb and 87Rb133Cs. In this thesis, I report the successful creation of a new species of ultracold polar ground-state molecules: 23Na39K. Starting from an ultracold mixture of bosonic 23Na and 39K atoms, weakly bound molecules are created. For this purpose, a Feshbach resonance in a high angular momentum scattering channel is chosen, experimentally identiﬁed and characterized. Close to this resonance the weakly bound Feshbach molecules are formed using resonant radio frequency radiation. For the two-photon ground-state transfer, a unique, highly specialized two-color laser system is designed and realized. It is used for one- and two-photon spectroscopy to identify the relevant transitions for the ground-state transfer. Based on the obtained data, a local model of the singlet-triplet mixed excited state manifolds is developed, with which the hyperﬁne structure and the magnetic ﬁeld dependence is predicted with high accuracy. According to these ﬁndings, a suitable pathway to a single hyperﬁne ground state is chosen considering selection rules and experimental conditions such as laser polarization and beam alignment. To precisely determine the two-photon resonance condition for STIRAP, electromagnetically induced transparency measurements are performed. The ground-state transfer is then performed using STIRAP. The experimental ﬁndings regarding the STIRAP are successfully supported theoretically by a model based on a ﬁve-level master equation. The pure molecular gas shows evidence for two-body dominated loss mechanisms, such as sticky four-body collisions. The molecule-atom mixture of 23Na39K+39K reveals an unexpectedly low loss rate coeﬃcient although sticky three-body collisions are assumed to occur. This behavior demands further investigations regarding diﬀerent hyperﬁne collisional chan-nels and magnetic ﬁeld regions.