We propose a scheme to directly measure the entangled W states with cross-Kerr nonlinearity mediums. find that well-designed structure can three-photon, four-photon and even N-photon in one step. Only PBSs mediums are used this scheme, which is feasible for experiments. explore measurement of three-photon extend it states.

This article considers spline smoothing of variance functions. We focus on selection of smoothing parameters and develop three direct data-driven methods: unbiased risk (UBR), generalized approximate cross validation (GACV) and generalized maximum likelihood (GML). In addition to guaranteed convergence, simulations show that these direct methods perform better than existing indirect UBR, genera...