Entanglement in a valence-bond solid state

The entanglement in a valence-bond solid state that describes the ground state of an Affleck-kennedy-Lieb-Tasaki quantum spin chain was investigated. It was observed that the entanglement was characterize between various subsystems of the ground state by calculating the entropy of one of the subsystems. It was also observed that the reduced density matrix of a continuous block of bulk spins was dependent on the size of the chain and the location of the block relative to the ends. It was found that the entanglement of the block with the rest of the sites approached a constant value exponentially fast, as the size of the block was increased.