  We study the formation of band gap bound states induced by a non-Hermitian
impurity embedded in a Hermitian system. We show that a pair of bound states
emerges inside the band gap when a parity-time ($\mathcal{PT}$) imaginary
potential is added in a strongly coupled bilayer lattices and the bound states
become strongly localized when the system approaches to the exceptional point
(EP). As a direct consequence of such $\mathcal{PT}$ impurity-induced bound
states, an impurity array can be constructed and protected by energy gap. The
effective Hamiltonian of the impurity array is non-Hermitian
Su-Schrieffer-Heeger (SSH) type and hosts Dirac probability-preserving
dynamics. We demonstrate the conclusion by numerical simulations for the
quantum transport of wave packet in right-angle bends waveguide and $Y$-beam
splitter. Our finding provides alternative way to fabricate quantum device by
non-Hermitian impurity.
