Experimental entanglement of six photons in graph states

Graph states^1,2,3—multipartite entangled states that can be represented by mathematical graphs—are important resources for quantum computation⁴, quantum error correction³, studies of multiparticle entanglement¹ and fundamental tests of non-locality^5,6,7 and decoherence⁸. Here, we demonstrate the experimental entanglement of six photons and engineering of multiqubit graph states^9,10,11. We have created two important examples of graph states, a six-photon Greenberger–Horne–Zeilinger state⁵, the largest photonic Schrödinger cat so far, and a six-photon cluster state², a state-of-the-art 'one-way quantum computer'⁴. With small modifications, our method allows us, in principle, to create various further graph states, and therefore could open the way to experimental tests of, for example, quantum algorithms^4,12 or loss- and fault-tolerant one-way quantum computation^13,14.