  A non-Hermitian interferometer can realize asymmetric transmission in the
presence of imaginary potential and magnetic flux. Here, we propose a
non-Hermitian dimer with an unequal hopping rate by an interferometer-like
cluster in the framework of tight-binding model. The intriguing features of
this design are the wave-vector independence and unidirectionality of
scattering, which amplifies wavepacket without distortion and absorbs
incoherent wave without reflection. The absorption relates to the system
spectral singularities, the dynamical behaviors of the spectral singularities
are also investigated analytically and numerically.
