  We create a six-qubit linear cluster state by transforming a two-photon
hyperentangled state in which three qubits are encoded in each particle, one in
the polarization and two in the linear momentum degrees of freedom. For this
state, we demonstrate genuine six-qubit entanglement, persistency of
entanglement against the loss of qubits, and higher violation than in previous
experiments on Bell inequalities of the Mermin type.
