title: Qubit entanglement between ring-resonator photon-pair sources on a silicon chip.
abstract: 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.
authors.affiliation: Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK.
authors.forename: J W
authors.initials: JW
authors.lastname: Silverstone
authors.affiliation: Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK.
authors.forename: R
authors.identifier: 0000000196450580
authors.initials: R
authors.lastname: Santagati
authors.affiliation: Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK.
authors.forename: D
authors.initials: D
authors.lastname: Bonneau
authors.affiliation: Institute of Photonics, Department of Physics, University of Strathclyde, Wolfson Centre, 106 Rottenrow East, Glasgow G4 0NW, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Strain
authors.affiliation: School of Engineering, University of Glasgow, James Watt South Building, Glasgow G12 8QQ, UK.
authors.forename: M
authors.initials: M
authors.lastname: Sorel
authors.affiliation: Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: O'Brien
authors.affiliation: Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK.
authors.forename: M G
authors.initials: MG
authors.lastname: Thompson