We show that an entanglement swapping operation performed with spontaneous parametric down-conversion can be made faithful without postselection using sum-frequency generation. This invites us to revisit the sum-frequency process and from a proof-of-principle experiment, we demonstrate that it provides a realistic solution for nonlinear optics at the single-photon level. This opens the way to attractive alternatives to six-photon protocols based on linear optics used, e.g., for the heralded creation of maximally entangled pairs or for device-independent quantum key distribution.

Abstract:We report a coherence-preserving photon frequency downconversion experiment based on difference-frequency generation in a periodically poled Lithium niobate waveguide, at the single-photon level. The coherence of the process has been demonstrated by measuring the phase coherence of pseudo single-photon time-bin qubits after frequency conversion with an interference visibility of > 96 %. This interface could be of interest for quantum repeater based hybrid networks.

Abstract. Manufacturing superconducting circuits out of ultrathin films is a challenging task when it comes to pattern complex compounds, which are likely to be deteriorated by the patterning process. With the purpose of developing high-Tc superconducting photon detectors, we designed a novel route to pattern ultrathin YBCO films down to the nanometric scale. We believe that our method, based on a specific use of a focused ion beam, consists in locally implanting Ga 3+ ions and/or defects instead of etching the film. This protocol could be of interest to engineer high-Tc superconducting devices (SQUIDS, SIS/SIN junctions, Josephson junctions), as well as to treat other sensitive compounds.PACS numbers: 85.25. Am, 81.16.Nd, 74.78.Bz, 81.15.Cd, 85.25.Pb Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process 2

We present recent results on our development of single photon detectors, including: gated and free-running InGaAs/InP avalanche photodiodes; hybrid detection systems based on sum-frequency generation and Si APDs; and SSPDs (superconducting single photon detectors), for telecom wavelengths; as well as SiPM (Silicon photomultiplier) detectors operating in the visible regime.