  The role of complex potentials in single-body Schr\H{o}dinger equation has
been studied intensively. We study the quantum coherence for degenerate Bose
gases in complex potentials, when the exchange symmetry of identical bosons is
considered. For initially independent Bose-Einstein condensates, it is shown
that even very weak imaginary potential can induce perfect quantum coherence
between different condensates. The scheme to observe imaginary potential
induced quantum coherence is discussed.
