  We derive a generalized wave-particle duality relation for arbitrary
multipath quantum interference phenomena. Beyond the conventional notion of the
wave nature of a quantum system, i.e., the interference fringe visibility, we
introduce a quantifier as the normalized quantum coherence, recently defined in
the framework of quantum information theory. To witness the particle nature, we
quantify the path distinguishability or the which-path information based on
unambiguous quantum state discrimination. Then, the Bohr complementarity
principle for multipath quantum interference can be stated as a duality
relation between the quantum coherence and the path distinguishability. For
two-path interference, the quantum coherence is identical to the interference
fringe visibility, and the relation reduces to the well-known complementarity
relation. The duality relation continues to hold in the case where mixedness is
introduced due to possible decoherence effects.
