  Quantum states can acquire a geometric phase called the Berry phase after
adiabatically traversing a closed loop, which depends on the path not the rate
of motion. The Berry phase is analogous to the Aharonov-Bohm phase derived from
the electromagnetic vector potential, and can be expressed in terms of an
Abelian gauge potential called the Berry connection. Wilczek and Zee extended
this concept to include non-Abelian phases -- characterized by the gauge
independent Wilson loop -- resulting from non-Abelian gauge potentials. Using
an atomic Bose-Einstein condensate, we quantum-engineered a non-Abelian SU(2)
gauge field, generated by a Yang monopole located at the origin of a
5-dimensional parameter space. By slowly encircling the monopole, we
characterized the Wilczek-Zee phase in terms of the Wilson loop, that depended
on the solid-angle subtended by the encircling path: a generalization of
Stokes' theorem. This observation marks the observation of the Wilson loop
resulting from a non-Abelian point source.

Atomic Physics;Quantum Gases;Quantum Physics