  Genuine 3-qubit entanglement comes in two different inconvertible types
represented by the Greenberger-Horne-Zeilinger (GHZ) state and the W state. We
describe a specific method based on local positive operator valued measures and
classical communication that can convert the ideal N-qubit GHZ state to a state
arbitrarily close to the ideal N-qubit W state. We then experimentally
implement this scheme in the 3-qubit case and characterize the input and the
final state using 3-photon quantum state tomography.
