  Reflectionless defects in Hermitian tight-binding lattices, synthesized by
the intertwining operator technique of supersymmetric quantum mechanics, are
generally not invisible and time-of-flight measurements could reveal the
existence of the defects. Here it is shown that, in a certain class of
non-Hermitian tight-binding lattices with complex hopping amplitudes, defects
in the lattice can appear fully invisible to an outside observer. The
synthesized non-Hermitian lattices with invisible defects possess a real-valued
energy spectrum, however they lack of parity-time (PT) symmetry, which does not
play any role in the present work.
