  Bright solitons in atomic Bose--Einstein condensates are a strong candidate
for high precision matter-wave interferometry, as their inherent stability
against dispersion supports long interrogation times. One analog to a beam
splitter for these solitons is a narrow potential barrier. A very narrow
barrier is desirable for interferometric purposes, but the width in a typical
realisation, using a blue-detuned optical dipole potential, is limited by the
wavelength of the laser light. We investigate a soliton interferometry scheme
using the geometric scalar potential experienced by atoms in a spatially
dependent dark state to overcome this limit. We propose a possible
implementation and numerically probe the effects of deviations from the ideal
configuration.
