  Aharonov-Bohm (AB) cage has a spectrum fully constituted by the flat bands
and has the capacity to confine arbitrary excitation. The confined excitation
in coupled waveguides propagates without diffraction. Exploited the
unidirectionality of the exceptional point (EP), we first propose the
non-Hermitian AB cage in the photonic crystal with inversion symmetry or
combined-inversion symmetry. Alternatively, the destructive interference of the
synthetic magnetic flux incorporated with gain and loss at the EP is then shown
to be able to induce the non-Hermitian AB cage. The spectrum of the
non-Hermitian AB cage is entirely constituted by the coalesced flat bands. The
light excitation is still confined regardless of the nonunitary dynamics caused
by the non-Hermiticity, but the localization area may alter. The non-Hermitian
AB caging can also be observed in the passive photonic crystals including
coupled waveguides. These findings pave the way of light control and
manipulation in the non-Hermitian integrated photonics.
