  We propose a method to generate entangled states of the vibrational modes of
N membranes which are coupled to a cavity mode via the radiation pressure.
Using sideband excitations, we show that arbitrary entangled states of
vibrational modes of different membranes can be produced in principle by
sequentially applying a series of classical pulses with desired frequencies,
phases and durations. As examples, we show how to synthesize several typical
entangled states, for example, Bell states, NOON states, GHZ states and W
states. The environmental effect, information leakage, and experimental
feasibility are briefly discussed. Our proposal can also be applied to other
experimental setups of optomechanical systems, in which many mechanical
resonators are coupled to a common sing-mode cavity field via the radiation
pressure.
