A tale of two species: Ultracold rubidium and strontium Stable mixtures, open-shell molecules and precision measurement

This thesis presents the physics and experimental techniques for successful production and investigations of ultracold Rb-Sr mixtures. Bose-Bose and Bose-Fermi mixtures where pursued with the intention of creating weakly bound molecules, while also offering rich insights into alkali – alkaline-earth systems. In the first part of this thesis, experiments with ⁸⁷Rb-⁸⁴Sr mixtures aiming at the creation of weakly bound molecules are described. We attempted magnetoassociation in ⁸⁷Rb-⁸⁴Sr Bose-Bose mixtures on a narrow Feshbach resonance at 1312 G magnetic field with a width of 1.69 mG. Motivated by the prospects of confinement-induced resonances and magnetoassociation in ⁸⁷Rb-⁸⁷Sr mixtures, the second part of this thesis presents experiments with resonantly interacting ultracold ⁸⁷Rb-⁸⁷Sr Bose-Fermi mixtures. The challenges posed by three-body losses in ⁸⁷Rb-⁸⁷Sr resonantly interacting Bose-Fermi mixtures are overcomed by demonstrating significant suppression of three-body recombination rate in 2D-confinement regimes. In the last part of this thesis, we demonstrated a unique co-magnetometry experiment, combining both ⁸⁷Sr and ⁸⁷Rb. We performed precision measurement of the g-factor of ground-state ⁸⁷Sr at the parts-per-million level using a co-magnetometry-like scheme. This experiment improved the measurement of the ⁸⁷Sr ground-state g-factor to a relative precision of 1.4 ppm. We also extracted for the first time the ratio of the magnetic moments between ⁸⁷Rb and ⁸⁷Sr to similar precision.