Non-Abelian geometric phases in a system of coupled quantum bits

A common strategy to measure the Abelian geometric phase for a qubit is to let it evolve along an orange-slice-shaped path connecting two antipodal points on the Bloch sphere by two different semi-great-circles. Since the dynamical phases vanish for such paths, this allows for direct measurement of the geometric phase. Here, we generalize the ``orange-slice'' setting to the non-Abelian case. The proposed method to measure the non-Abelian geometric phase can be implemented in a cyclic chain of four qubits with controllable interactions.