  Bright solitons in atomic Bose--Einstein condensates are strong candidates
for high precision matter-wave interferometry, as their inherent stability
against dispersion supports long interrogation times. An analog to a beam
splitter is then a narrow potential barrier. A very narrow barrier is desirable
for interferometric purposes, but in a typical realisation using a blue-detuned
optical dipole potential, the width is limited by the laser wavelength. 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.
