We numerically study the classical and quantum dynamics of an atomic bright soliton in a highly elongated one dimensional harmonic trap with a Gaussian barrier. In the regime of the recent experiment by Dyke et al the system realizes a coherent nonlinear soliton beam-splitter and interferometer whose accuracy we analyze. In the case of tighter radial trap confinement and enhanced quantum fluctuations, a split soliton can represent a spin-squeezed, or alternatively, a fragmented condensate with reduced phase coherence that can be measured by interfering the split soliton by the barrier. We also find large quantum mechanical uncertainties in the soliton’s position and momentum due to nonlinear interaction with the barrier.