Article

# A photonic quantum information interface

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Group of Applied Physics, University of Geneva, 1211 Geneva 4, Switzerland.
(Impact Factor: 41.46). 08/2005; 437(7055):116-120. DOI: 10.1038/nature04009
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ABSTRACT

Quantum communication requires the transfer of quantum states, or quantum bits of information (qubits), from one place to another. From a fundamental perspective, this allows the distribution of entanglement and the demonstration of quantum non-locality over significant distances. Within the context of applications, quantum cryptography offers a provably secure way to establish a confidential key between distant partners. Photons represent the natural flying qubit carriers for quantum communication, and the presence of telecommunications optical fibres makes the wavelengths of 1,310 nm and 1,550 nm particularly suitable for distribution over long distances. However, qubits encoded into alkaline atoms that absorb and emit at wavelengths around 800 nm have been considered for the storage and processing of quantum information. Hence, future quantum information networks made of telecommunications channels and alkaline memories will require interfaces that enable qubit transfers between these useful wavelengths, while preserving quantum coherence and entanglement. Here we report a demonstration of qubit transfer between photons of wavelength 1,310 nm and 710 nm. The mechanism is a nonlinear up-conversion process, with a success probability of greater than 5 per cent. In the event of a successful qubit transfer, we observe strong two-photon interference between the 710 nm photon and a third photon at 1,550 nm, initially entangled with the 1,310 nm photon, although they never directly interacted. The corresponding fidelity is higher than 98 per cent.

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• "To manipulate the bichromatic qubit we perform quantum frequency conversion (QFC) on the generated single photons. QFC has been demonstrated using second order χ (2) nonlinearities either via sum-frequency generation (16,17,222324252627or electro-optic modulation (13–15,30). In contrast, Bragg scattering four-wave mixing is a third order χ (3) nonlinear process that has also been shown to be an effective (18–21) way of achieving QFC which can be applied in many types of waveguide platforms. "
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• "Single-photon sources are a fundamental resource in 16 quantum optics, with a broad range of applications [1] [2] [3] [4]. "
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Full-text · Article · Sep 2015 · Physical Review A
• "To manipulate the bichromatic qubit we perform quantum frequency conversion (QFC) on the generated single photons. QFC has been demonstrated using second order χ (2) nonlinearities either via sum-frequency generation (16,17,222324252627or electro-optic modulation (13–15,30). In contrast, Bragg scattering four-wave mixing is a third order χ (3) nonlinear process that has also been shown to be an effective (18–21) way of achieving QFC which can be applied in many types of waveguide platforms. "
##### Article: Ramsey interferometry for manipulation of single photons
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ABSTRACT: We demonstrate a Ramsey interferometer for single photons via consecutive quantum frequency conversions where the phase depends on the propagation between the two interaction regions. Such an interferometer offers control over frequency encoded quantum states.
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