  We consider a two-mode model describing scalar bosons with two-body
interactions in a single trap, taking into account coherent pair-exchange
between the modes. It is demonstrated that the resulting fragmented many-body
states with continuous (nonsingular) Fock-space distribution amplitudes are
robust against perturbations due to occupation number and relative phase
fluctuations, Josephson-type tunneling between the modes, and weakly broken
parity of orbitals, as well as against perturbations due to interaction with a
third mode.
