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Japanese Journal of Applied Physics

Violation of Bell's Inequality in 1550 nm Band without Subtraction of Accidental Coincidences

Akio Yoshizawa, Hidemi Tsuchida

Published Mar 1, 2005• 7 citations
Publisher

Abstract

A violation of Bell's inequalities using quantum entanglement indicates the nonlocality of two particles such as photons and electrons. We observe a violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality, a particular Bell's inequality, in polarization-entangled photon pairs in the 1550 nm band. For photon pair generation based on spontaneous parametric down conversion, a fiber-optic two-photon interferometer with two periodically poled lithium niobate waveguides is adopted. The obtained S value of the CHSH inequality is 2.44 ±0.02 without subtraction of accidental coincidences, yielding a violation by ∼22 standard deviations in an hour. Two-photon interference with a visibility of 0.885 is also observed. If those coincidences are subtracted, the visibility becomes almost unity.

DOI
10.1143/jjap.44.l375

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A violation of Bell's inequalities using quantum entanglement indicates the nonlocality of two particles such as photons and electrons. We observe a violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality, a particular Bell's inequality, in polarization-entangled photon pairs in the 1550 nm band. For photon pair generation based on spontaneous parametric down conversion, a fiber-optic two-photon interferometer with two periodically poled lithium niobate waveguides is adopted. The obtained S value of the CHSH inequality is 2.44 ±0.02 without subtraction of accidental coincidences, yielding a violation by ∼22 standard deviations in an hour. Two-photon interference with a visibility of 0.885 is also observed. If those coincidences are subtracted, the visibility becomes almost unity.
We report a source of polarization-entangled photon pairs in the 1550-nm telecommunication band, which is based on non-collinear spontaneous parametric down-conversion in a periodically poled lithium niobate crystal pumped by picosecond pulses. This source is realized utilizing a polarization-based Sagnac interferometer employing a type-0 non-collinear quasi-phase-matching configuration. Polarization entanglement is verified through measurement of the polarization-correlation interference fringes with visibility >96% and by testing the experimental violation of the Clauser-Horne-Shimony-Holt (CHSH) form of Bell's inequality. The CHSH-Bell parameter S is found to be 2.72 ± 0.04, with 18 standard deviations from the statistical uncertainty.
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.
Abstract In addition to Bell's original inequality, John Clauser, Michael Horne, Abner Shimony, and Richard Holt (CHSH) developed a special form of Bell's inequality which gives classical limits to the expected correlation between two particles. We present a theoretical demonstration of the maximum value for violation of CHSH inequality, S = 2 2\sqrt{2}2​ , for the pure entangled quantum state. Using the spontaneous four‐wave mixing process, we generate polarization‐entangled photon pairs in a highly nonlinear fiber (HNLF) loop, for experimental verification. Using a nonentangled quantum state, we show theoretically that the violation of CHSH inequality is only a property of entangled states. We also show the theoretical solution of violation of the CHSH inequality for a general Greenberger–Horne–Zeilinger state and for an arbitrary state of two particles. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2454–2461, 2012; View this article online at wileyonlinelibrary. com. DOI 10.1002/mop.27127