Article

Long-distance distribution of time-bin entangled photon pairs over 100 km using frequency up-conversion detectors

Osaka University, Suika, Ōsaka, Japan
Optics Express (Impact Factor: 3.53). 11/2007; 15(21):13957-64. DOI: 10.1364/OE.15.013957
Source: PubMed

ABSTRACT We report an experimental demonstration of the distribution of time-bin entangled photon pairs over 100 km of optical fiber. In our experiment, 1.5-mum non-degenerated time-bin entangled photon pairs were generated with a periodically poled lithium niobate (PPLN) waveguide by using the parametric down conversion process. Combining this approach with ultra-low-loss filters to eliminate the pump light and separate signal and idler photons, we obtained an efficient entangled photon pair source. To detect the photons, we used single-photon detectors based on frequency up-conversion. These detectors operated in a non-gated mode so that we could use a pulse stream of time correlated entangled photon pairs at a high repetition frequency (1 GHz). Using these elements, we distributed time-bin entangled photon pairs over 100 km of dispersion shifted fiber and performed a two-photon interference experiment. We obtained a coincidence fringe of 81.6% visibility without subtracting any background noise, such as accidental coincidence or dark count, which was good enough to violate Bell's inequality. Thus, we successfully distributed time-bin entangled photon pairs over 100 km.

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    • "The detection efficiency problem for photons is very complicated and its solution was based on the use of advanced photo-detectors, i.e., new technology as well as its testing [24]. The Bell tests with photons [11]–[13] are promising to close both the detection and locality loopholes, since the latter was closed long ago [25] and recently experiments demonstrating violation of Bell-type inequalities on large distances [26]–[33] were performed. However, to violate Bell type inequalities one has to approach very high efficiency of the total experimental setup. "
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    • "Nowadays, quantum communication links can be established over considerable distances using the art fibre technology [1],[19]– [21]. Indeed, up to 100 km entanglement distributions have been created in optical fibres [18]–[24]. The confinements of the photons to a fibre has certain drawbacks. "
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