  Using a three-dimensional spin polarimeter we have gathered evidence for the
interference of spin states in photoemission from the surface alloy Sb/Ag(111).
This system features a small Rashba-type spin-splitting of a size comparable to
the linewidth of the quasiparticles, thus causing an intrinsic overlap between
states with orthogonal spinors. Besides a small spin polarization caused by the
spin-splitting, we observe a large spin polarization component in the plane
normal to the quantization axis provided by the Rashba effect. Strongly
suggestive of coherent spin rotation, this effect is largely independent of the
photon energy and photon polarization.
