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arXiv:quant-ph/0508215 · Physical Review A

Generation of 1.5−μm band time-bin entanglement using spontaneous fiber four-wave mixing and planar light-wave circuit interferometers

Hiroki Takesue, Kyo Inoue

Published Oct 19, 2005• 111 citations
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Abstract

This paper reports $1.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ band time-bin entanglement generation. We employed a spontaneous four-wave mixing process in a dispersion shifted fiber, with which correlated photon pairs with very narrow bandwidths were generated efficiently. To observe two-photon interference, we used planar lightwave circuit based interferometers that were operated stably without feedback control. As a result, we obtained coincidence fringes with 99% visibilities after subtracting accidental coincidences, and successfully distributed entangled photons over 20-km standard single-mode fiber without any deterioration in the quantum correlation.

DOI
10.1103/physreva.72.041804

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This paper reports 1.5\ensuremath-\ensuremathμm1.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}1.5\ensuremath-\ensuremathμm band time-bin entanglement generation. We employed a spontaneous four-wave mixing process in a dispersion shifted fiber, with which correlated photon pairs with very narrow bandwidths were generated efficiently. To observe two-photon interference, we used planar lightwave circuit based interferometers that were operated stably without feedback control. As a result, we obtained coincidence fringes with 99% visibilities after subtracting accidental coincidences, and successfully distributed entangled photons over 20-km standard single-mode fiber without any deterioration in the quantum correlation.
This paper reports the first demonstration of the generation and distribution of time-bin entangled photon pairs in the 1.5-microm 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.
We report the generation of polarization entangled photon pairs in the 1550-nm wavelength band using spontaneous four-wave mixing in a dispersion-shifted fiber loop. The use of the fiber-loop configuration made it possible to generate polarization entangled states very stably. With accidental coincidences subtracted, we obtained coincidence fringes with >90>90%>90 visibilities, and observed a violation of Bell's inequality by seven standard deviations. We also confirmed the preservation of the quantum correlation between the photons even after they had been separated by 20 km of optical 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
We generate photon pairs at telecom wavelength through a spontaneous four-wave mixing process in a short 10 m of highly nonlinear fiber. We use a counterpropagating scheme to generate a correlated and entangled photon pair. We observe coincidence to accidental-coincidence ratio of 29±3 at room temperature (300 K) and as high as 130±5 when the fiber is cooled to liquid-nitrogen temperature (77 K). Two-photon interference with visibility >98% (>92%) and the violation of Bell's inequality by >12 (≈5) standard deviation are observed at 77 K (300 K), respectively, without subtracting accidental-coincidence count. We obtain a photon-pair production rate about factor 3(2) higher than a 300 m dispersion-shifted fiber at 300 K (77 K).
We report the first entanglement swapping experiment using entangled photon-pair sources based on spontaneous four-wave mixing (SFWM). The 1.5-microm band entangled photon pairs generated by SFWM in two independent 500-m dispersion shifted fibers exhibited quantum interference, thanks to the negligible walk-off between the pump and photon pairs. The use of 500-MHz gated-mode InGaAs/InP avalanche photodiodes based on the sine-wave gating technique increased the fourfold coincidence rate. As a result, the formation of an entanglement between photons from independent sources was successfully observed.