  We show that quantum walks interpolate between a coherent `wave walk' and a
random walk depending on how strongly the walker's coin state is measured;
i.e., the quantum walk exhibits the quintessentially quantum property of
complementarity, which is manifested as a trade-off between knowledge of which
path the walker takes vs the sharpness of the interference pattern. A physical
implementation of a quantum walk (the quantum quincunx) should thus have an
identifiable walker and the capacity to demonstrate the interpolation between
wave walk and random walk depending on the strength of measurement.
