  Under appropriate external conditions a semiconductor nanowire in proximity
to an s-wave superconductor can be in a topological superconducting (TS) phase.
This phase supports localized zero-energy Majorana fermions at the ends of the
wire. However, the non-Abelian exchange statistics of Majorana fermions is
difficult verify because of the one-dimensional topology of such wires. In this
paper we propose a scheme to transport Majorana fermions between the ends of
different wires using tunneling, which is shown to be controllable by gate
voltages. Such tunneling-generated hops of Majorana fermions can be used to
exchange the Majorana fermions. The exchange process thus obtained is described
by a non-Abelian braid operator that is uniquely determined by the
well-controlled microscopic tunneling parameters.
