Observation of eight-photon entanglement

The creation of increasingly large multipartite entangled states is not only a fundamental scientific endeavour in itself1,2,3, but is also the enabling technology for quantum information4,5. Tremendous experimental effort has been devoted to generating multiparticle entanglement with a growing number of qubits6,7,8,9,10,11,12,13,14,15,16. So far, up to six spatially separated single photons10,11,12,13,14 have been entangled based on parametric downconversion17. Multiple degrees of freedom of a single photon have been exploited to generate forms of hyper-entangled states18,19. Here, using new ultra-bright sources of entangled photon pairs20, an eight-photon interferometer and post-selection detection, we demonstrate for the first time the creation of an eight-photon Schrödinger cat state1 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 simulation21,22, topological error correction23 and testing entanglement dynamics under decoherence24. Researchers demonstrate the creation of an eight-photon Schrödinger-cat state with genuine multipartite entanglement by developing noise-reduction multiphoton interferometer and post-selection detection. The ability to control eight individual photons will enable new multiphoton entanglement experiments in previously inaccessible parameter regimes.