  Based on the complementarity relation between entanglement of a composite
system and the purity of a subsystem, we propose a simple method to measure the
amount of entanglement. The method can be applied to a bipartite system in a
pure state of any arbitrary dimension. It requires only single qudit rotations
and straightforward probability measurements performed on one of the
subsystems, and can thus be easily implemented experimentally using linear
optical devices.
