Observation of eight-photon entanglement

The creation of increasingly large multipartite entangled states is not only a fundamental scientific endeavour in itself(1-3), but is also the enabling technology for quantum information(4,5). Tremendous experimental effort has been devoted to generating multiparticle entanglement with a growing number of qubits(6-16). So far, up to six spatially separated single photons(10-14) have been entangled based on parametric downconversion(17). Multiple degrees of freedom of a single photon have been exploited to generate forms of hyper-entangled states(18,19). Here, using new ultra-bright sources of entangled photon pairs(20), an eight-photon interferometer and post-selection detection, we demonstrate for the first time the creation of an eight-photon Schrodinger cat state(1) with genuine multipartite entanglement. The ability to control eight individual photons represents a step towards optical quantum computation, and will enable new experiments on, for example, quantum simulation(21,22), topological error correction(23) and testing entanglement dynamics under decoherence(24).