Geometrical phases for the G(4,2) Grassmannian manifold

We generalize the usual Abelian Berry phase generated for example in a system with two nondegenerate states to the case of a system with two doubly degenerate energy eigenspaces. The parametric manifold describing the space of states of the first case is formally given by the G(2,1) Grassmannian manifold, while for the generalized system it is given by the G(4,2) one. For the latter manifold which exhibits a much richer structure than its Abelian counterpart we calculate the connection components, the field strength and the associated geometrical phases that evolve nontrivially both of the degenerate eigenspaces. A simple atomic model is proposed for their physical implementation.