  In this paper we study a novel superconductor-ferromagnet-superconductor
(SC-FM-SC) Josephson junction array deposited on top of a two-dimensional
quantum spin Hall (QSH) insulator. The existence of Majorana bound states at
the interface between SC and FM gives rise to charge-e tunneling, in addition
to the usual charge-2e Cooper pair tunneling, between neighboring
superconductor islands. Moreover, because Majorana fermions encode the
information of charge number parity, an exact Z_2 gauge structure naturally
emerges and leads to many new insulating phases, including a deconfined phase
where electrons fractionalize into charge-e bosons and topological defects. A
new superconductor-insulator transition has also been found.
