  Two majorana Fermions (MFs) localized at the two ends of the topological
superconducting wire can interfere with each other and form the well known
$4\pi$ Josephson current. We reveal that the density of states (Dos) for the
electron part and the hole part also follow a parity correlated $4\pi$ period
oscillation, while the Dos displays a $2\pi$ period oscillation when two
trivial states interfere with each other. Thus, the period of Dos oscillation
can be used to distinguish the MFs from the trivial localized states.
Interestingly, such phenomena can be directly observed in a short
superconducting wire controlled by the gate voltage. This largely simplifies
the experimental setup. We suggest that the interference effects can be
detected through two STM leads or two norm leads.
