Atomic ultracold mixtures have been realized with very different species or with different internal states of one species. The latter system offers a unique possibility to coherently interchange the constituents of the mixture offering a new degree of freedom which is under pristine experimental control. By interpreting a mixture of two components as a pseudo-spin-1/2 system, one can realize in good approximation an XXX-Heisenberg model with single-ion anisotropy and precisely controllable transverse field. This is a model system exhibiting a reach phase diagram including an experimentally accessible quantum phase transition. The experimental system is especially interesting for the study of dynamics which is theoretically very challenging to be predicted. In this lecture the fundamental properties of coherently coupled two-component gases will be discussed and the results on probing the quantum critical point with dynamics after a fast quench will be presented.