title: Two-photon interference at telecom wavelengths for time-bin-encoded single photons from quantum-dot spin qubits.
abstract: Practical quantum communication between remote quantum memories rely on single photons at telecom wavelengths. Although spin-photon entanglement has been demonstrated in atomic and solid-state qubit systems, the produced single photons at short wavelengths and with polarization encoding are not suitable for long-distance communication, because they suffer from high propagation loss and depolarization in optical fibres. Establishing entanglement between remote quantum nodes would further require the photons generated from separate nodes to be indistinguishable. Here, we report the observation of correlations between a quantum-dot spin and a telecom single photon across a 2-km fibre channel based on time-bin encoding and background-free frequency downconversion. The downconverted photon at telecom wavelengths exhibits two-photon interference with another photon from an independent source, achieving a mean wavepacket overlap of greater than 0.89 despite their original wavelength mismatch (900 and 911 nm). The quantum-networking operations that we demonstrate will enable practical communication between solid-state spin qubits across long distances.
authors.affiliation: E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.
authors.forename: Leo
authors.initials: L
authors.lastname: Yu
authors.affiliation: E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.|National Institute of Informatics, Hitotsubashi 2-1-2, Tokyo 101-8403, Japan.|School of Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Chandra M
authors.initials: CM
authors.lastname: Natarajan
authors.affiliation: National Institute of Informatics, Hitotsubashi 2-1-2, Tokyo 101-8403, Japan.|Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Horikiri
authors.affiliation: E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.
authors.forename: Carsten
authors.initials: C
authors.lastname: Langrock
authors.affiliation: Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, California 94304, USA.
authors.forename: Jason S
authors.initials: JS
authors.lastname: Pelc
authors.affiliation: Scottish Universities Physics Alliance (SUPA) and School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Tanner
authors.affiliation: National Institute of Informatics, Hitotsubashi 2-1-2, Tokyo 101-8403, Japan.
authors.forename: Eisuke
authors.initials: E
authors.lastname: Abe
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Center for Complex Material Systems, University of Würzburg, Am Hubland, Würzburg 97074, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Maier
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Center for Complex Material Systems, University of Würzburg, Am Hubland, Würzburg 97074, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schneider
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Center for Complex Material Systems, University of Würzburg, Am Hubland, Würzburg 97074, Germany.|School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK.
authors.forename: Sven
authors.initials: S
authors.lastname: Höfling
authors.affiliation: Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Center for Complex Material Systems, University of Würzburg, Am Hubland, Würzburg 97074, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Kamp
authors.affiliation: School of Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Hadfield
authors.affiliation: E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.
authors.forename: Martin M
authors.initials: MM
authors.lastname: Fejer
authors.affiliation: E. L. Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.|National Institute of Informatics, Hitotsubashi 2-1-2, Tokyo 101-8403, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Yamamoto