Physics of ultracold spin mixtures in low and stable magnetic field environment

A high degree of control over the magnetic field is required in many ultracold atom experiments. On the one hand, magnetic field stability sets the fundamental limit for observing phenomena in coherently coupled superfluid mixtures. In our laboratory, a magnetic shield ensures field stability at the microGauss level, enabling the observation of the quantum phase transition in a ferromagetic atomic mixture, the investigation of its static properties and the study of dynamical properties such as the local decay of the metastable state into the true ground state, resulting in the probabilistic nucleation of bubbles. In particular, this thesis focuses on the temperature dependence of this decay mechanism. On the other hand, the magnetic field magnitude determines the strength of the Zeeman contribution to the system's energy. In this context, I discuss efforts to minimize the magnetic field in order to access a novel quantum phase in which the interaction energy dominates over all the other relevant energy scales, such that the system's evolution is governed solely by interactions.