Generalized Type II Fusion of Cluster States

Abstract: Measurement based quantum computation is a quantum computing paradigm, that employs single-qubit measurements performed on an entangled resource state in the form of a cluster state. A basic ingredient in the construction of the resource state is the type II fusion procedure, which connects two cluster states. We generalize the type II fusion procedure by generalizing the fusion matrix, and classify the resulting final states, which also include cluster states up to single-qubit rotations. We prove that the probability for the success of the generalized type II fusion is bounded by fifty percent, and classify all the possibilities to saturate the bound. We analyze the enhancement of the fusion success probability above the fifty percent bound, by the reduction of the entanglement entropy of the fusion link. We prove that the only states, that can be obtained with hundred percent probability of success, are product states.