  We study the wave-particle duality in a general Mach-Zehnder interferometer
with an asymmetric beam splitter from the viewpoint of quantum information
theory. The correlations(including the classical correlation and the quantum
correlation) between the particle and the which-path detector are derived when
they are in pure state or mixed state at the output of Mach-Zehnder
interferometer. It is found that the fringe visibility and the correlations are
effected by the asymmetric beam splitter and the input state of the particle.
The complementary relations between the fringe visibility and the correlations
are also presented.
