Generation of free-travelling four-mode cluster-type entangled coherent states

A new scheme is proposed to generate free-travelling four-mode cluster-type entangled coherent states. Compared with other previously proposed schemes ours is very simple in execution using only one π-cross-Kerr medium, two 50:50 beam-splitters and two π/2-phase-shifters. Despite the setup simplicity, our scheme, unlike the others which are all probabilistic, is efficient with 100% success probability since no measurements are involved at all.