  The dynamics of an atom waveguide X-junction beam splitter becomes truly 1D
in a regime of low temperatures and densities and large positive scattering
lengths where the transverse mode becomes frozen and the many-body Schrodinger
dynamics becomes exactly soluble via a generalized Fermi-Bose mapping theorem.
We analyze the interferometric response of a double-X interferometer of this
type due to potential differences between the interferometer arms.
