  We propose the $2\pi$-periodic Aharonov-Bohm (AB) effect as a nonlocal probe
of Majorana zero modes (MZMs) without the restriction of fermion parity. We
demonstrate the enhancement of the AB effect, where the topological protection
of MZMs yields amplified and robust Andreev reflection mediated by MZMs at
multiple superconductor-normal metal junctions. We investigate the influence of
trivial bound states and show that a nonlocal index enables a more explicit
distinction between the trivial and topological bound states than local probes.
