Qubit entanglement between ring-resonator photon-pair sources on a silicon chip

Silverstone, J.W. and Santagati, R. and Bonneau, D. and Strain, M.J. and Sorel, M. and O'Brien, J.L. and Thompson, M.G. (2015) Qubit entanglement between ring-resonator photon-pair sources on a silicon chip. Nature Communications, 6. 7948. ISSN 2041-1723 (https://doi.org/10.1038/ncomms8948)

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Entanglement - one of the most delicate phenomena in nature - is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale.