Entanglement enhancement through multi-rail noise reduction for   continuous-variable measurement-based quantum information processing
  We study theoretically the teleportation of controlled-phase (CZ) gate through measurement-based quantum information processing for continuous-variable systems. We examine the degree of entanglement in the output modes of the teleported CZ-gate for two classes of resource states: the canonical cluster states that are constructed via direct implementations of two-mode squeezing operations, and the linear-optical version of cluster states which are built from linear-optical networks of beam splitters and phase shifters. In order to reduce the excess noise arising from finite-squeezed resource states, teleportation through resource states with different multi-rail designs will be considered and the enhancement of entanglement in the teleported CZ-gates will be analyzed. For multi-rail cluster with an arbitrary number of rails, we obtain analytical expressions for the entanglement in the output modes and analyze in detail the results for both classes of resource states. At the same time, we also show that for uniformly squeezed clusters the multi-rail noise reduction can be optimized when the excess noise is allocated uniformly to the rails. To facilitate the analysis, we develop a trick with manipulations of quadrature operators that can reveal rather efficiently the measurement sequence and corrective operations needed for the measurement-based gate teleportation, which will also be explained in detail. 
Yung-Chao Su and Shin-Tza Wu
quant-ph