  The semiclassical evolution of spinning particles has recently been
re-examined in condensed matter physics, high energy physics, and optics,
resulting in the prediction of the intrinsic spin Hall effect associated with
the Berry phase. A fundamental nature of this effect is related to the
spin-orbit interaction and topological monopoles. Here we report a unified
theory and a direct observation of two mutual phenomena: a spin-dependent
deflection (the spin Hall effect) of photons and the precession of the Stokes
vector along the coiled ray trajectory of classical geometrical optics. Our
measurements are in perfect agreement with theoretical predictions, thereby
verifying the dynamical action of the topological Berry-phase monopole in the
evolution of light. These results may have promising applications in
nano-optics and can be immediately extrapolated to the evolution of massless
particles in a variety of physical systems.
