Experimental demonstration of a hyper-entangled ten-qubit Schrödinger cat state

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Wei-Bo Gao, et. al. Nature Physics March 2010. doi:10.1038/nphys1603

Coherent manipulation of a large number of qubits and the generation of entangled states between them has been an important goal and benchmark in quantum information science, leading to various applications such as measurement-based quantum computing and high-precision quantum metrology. However, the experimental preparation of multiparticle entanglement remains challenging. Using atoms, entangled states of up to eight qubits have been created, and up to six photons have been entangled. Here, by exploiting both the photons’ polarization and momentum degrees of freedom, we experimentally generate hyper-entangled six-, eight- and ten-qubit Schrödinger cat states with verified genuine multi-qubit entanglement. We also demonstrate super-resolving phase measurements enhanced by entanglement, with a precision to beat the standard quantum limit. Modifications of the experimental set-up would enable the generation of other graph states up to ten qubits. Our method offers a way of expanding the effective Hilbert space and should provide a versatile test-bed for various quantum applications.