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Optics Express

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

Toshimori Honjo, Hiroki Takesue, Hidehiko Kamada, Y. Nishida, Osamu Tadanaga, Masaki Asobe, Kyo Inoue

Published Jan 1, 2007• 74 citations

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.

DOI: 10.1364/oe.15.013957

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1 Long-Distance Distribution of Time-Bin Entanglement Generated in a Cooled Fiber

This paper reports the first demonstration of the generation and distribution of entangled photon pairs in the 1.5-µm band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences. 2 The entangled states of quantum particles constitute the quintessential feature of quantum mechanics because they highlight its non-locality most vividly [1]. Moreover, entanglements form the basis of quantum information, and facilitate such applications as quantum key distribution (QKD) [2, 3], quantum teleportation [4], and quantum repeaters [5]. Of the many forms of entanglement, entangled photons are important because they are suitable for distributing quantum information over long distances. Although several good sources are available in the short wavelength band [6, 7], an entangled photon-pair source in the 1.5-µm band is needed if we

•Jan 1, 2008•0 citations

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.

We describe our recent experiment on the distribution of time-bin entangled photon pairs over 300 km of optical fiber, which set a record for long-distance distribution of quantum information.This experiment was achieved by using a high-speed and high signal-to-noise ratio entanglement generation/evaluation setup consisting of periodically poled lithium niobate waveguides and superconducting singlephoton detectors.We observed the violation of Bell's inequality and thus confirmed that the entangled photon pairs preserved the quantum correlation after they were separated by 300 km of fiber.

We have experimentally implemented a non-degenerate sequential time-bin entangled photon-pair source using a periodically poled potassium titanyl phosphate waveguide at a clock rate of 1 GHz. The wavelengths of the signal and idler are 895 nm and 1310 nm, which are suitable for local and long distance optical communications, respectively and the 895 nm signal is also suitable for quantum memory research. A silicon avalanche photodiode is used to detect the photons at 895 nm while a periodically poled lithium niobate waveguide based up-conversion detector is used to detect the photons at 1310 nm. The measured entangled-photon-pair flux rate is 650 Hz and the fringe visibility for two-photon interference is 79.4% without noise subtraction.

Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mum pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides. We report what we believe to be a new method using cascaded second-order nonlinearity in a single PPLN waveguide to produce high-purity time-bin entangled photon pairs. We confirmed the generation of entanglement through a two-photon interference experiment showing a coincidence fringe with a visibility of up to 97%.

This paper reports the first demonstration of the generation and distribution of entangled photon pairs in the 1.5-µm band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences. 2 The entangled states of quantum particles constitute the quintessential feature of quantum mechanics because they highlight its non-locality most vividly [1]. Moreover, entanglements form the basis of quantum information, and facilitate such applications as quantum key distribution (QKD) [2, 3], quantum teleportation [4], and quantum repeaters [5]. Of the many forms of entanglement, entangled photons are important because they are suitable for distributing quantum information over long distances. Although several good sources are available in the short wavelength band [6, 7], an entangled photon-pair source in the 1.5-µm band is needed if we