In Chap. 2 , we have outlined that mixtures of atomic gases are much more flexible due to the large variety of atomic species, characterized by different states, the possibility of generating coherently coupled configurations, and tuning the interaction between the different components of the mixture. To study such exotic gases at ultra-low temperatures, Bose-Einstein condensed mixtures were first realized experimentally by the JILA group in 1997 [1]. Owing to the possibility of tuning the intercomponent scattering lengths by using Feshbach resonances, two-component quantum liquids exhibit rich physics that is not accessible in a single-component fluid. Therefore, theoretical [2, 3] and experimental studies [4–7] have revealed that, the nature of this physics dramatically depends on the sign of the intercomponent coupling constant \(g_{12}\) .