  Semiconductor-superconductor hybrid systems are promising candidates for the
realization Majorana fermions and topological order, i.e. topologically
protected degeneracies, in solid state devices. We show that the topological
order is mirrored in the excitation spectra and can be observed in nonlinear
Coulomb blockade transport through a ring-shaped nanowire. Especially, the
excitation spectrum is almost independent of magnetic flux in the topologically
trivial phase but acquires a characteristic $h/e$ magnetic flux periodicity in
the nontrivial phase. The transition between the trivial and nontrivial phase
is reflected in the closing and reopening of an excitation gap. We show that
the signatures of topological order are robust against details of the geometry,
electrostatic disorder, and the existence of additional subbands and only rely
on the topology of the nanowire and the existence of a superconducting gap.
Finally, we show that the coherence length in the nontrivial phase is much
longer than in the trivial phase. This opens the possibility to coat the
nanowire with superconducting nanograins and thereby significantly reduce the
current due to cotunneling of Cooper pairs and to enhance the Coulomb charging
energy without destroying the superconducting gap.
