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Applied Physics Letters

Efficient source of high purity polarization-entangled photon pairs in the 1550nm telecommunication band

Tae-Gon Noh, Heonoh Kim, Taehyoung Zyung, Jaewan Kim

Published Jan 1, 2007• 10 citations
Publisher

Abstract

The authors present an efficient source of high purity polarization-entangled photon pairs in the standard 1550nm telecommunication band using a type-II degenerate parametric downconversion process. They first measured the spatial intensity distributions of the downconverted light to verify the beamlike, collinear, and noncollinear generations at the 1550nm wavelength. All four Bell states could easily be generated by selecting the intersection of two downconverted light cones in the noncollinear phase matching. They observed two-photon fringe visibilities of up to 98±3% and violations of Bell’s inequality by up to nine standard deviations when the accidental coincidences were subtracted.

DOI
10.1063/1.2429025

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The authors present an efficient source of high purity polarization-entangled photon pairs in the standard 1550nm telecommunication band using a type-II degenerate parametric downconversion process. They first measured the spatial intensity distributions of the downconverted light to verify the beamlike, collinear, and noncollinear generations at the 1550nm wavelength. All four Bell states could easily be generated by selecting the intersection of two downconverted light cones in the noncollinear phase matching. They observed two-photon fringe visibilities of up to 98±3% and violations of Bell’s inequality by up to nine standard deviations when the accidental coincidences were subtracted.
We report on a high-intensity source of polarization-entangled photon pairs with high momentum definition. Type-II noncollinear phase matching in parametric down conversion produces true entanglement: No part of the wave function must be discarded, in contrast to previous schemes. With two-photon fringe visibilities in excess of 97%, we demonstrated a violation of Bell's inequality by over 100 standard deviations in less than 5 min. The new source allowed ready preparation of all four of the EPR-Bell states.
We present a source of noncollinear correlated photon pairs in the standard 1550 nm telecommunication band. They are generated by a spontaneous parametric down-conversion process and emitted in a cone because of type-I noncollinear phase matching. Within the band, the source gives a completely flexible choice of the frequencies of the photon pairs, and correlation properties related to spatial momentum as well as energy and time can easily be utilized.We characterize the source by measuring the spatial intensity distribution of the down-converted light and by performing coincidence counting.
The design and implementation of a novel source of degenerate polarization entangled photon pairs in the telecom band, based on a cavity enhanced parametric downconversion process, is presented. Two of the four maximally entangled Bell states are produced; the remaining two are obtainable by the addition of a half wave plate into the setup. The coincident photon detection rate in the A/D basis between two detectors at the output of the device revealed the production of highly entangled states, resulting in quantum interference visibilities of 0.971 ± 0.041 (ϕ = 0 state) and 0.932 ± 0.036 (ϕ = π state) respectively. The entangled states were found to break the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by around 6 standard deviations. From the measured coincidence counting rates and the optical system losses, an entangled photon pair production rate of 8.9 × 10(4) s(-1) mW(-1) pump was estimated.
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 experimentally demonstrate the direct generation of polarization-entangled photon pairs in an optical fiber at room temperature by exploiting type-II phase-matched spontaneous parametric down-conversion. A second-order nonlinearity is artificially induced in the 17-cm-long weakly birefringent step-index fiber through the process of thermal poling, and quasi-phase-matching allows for the generation of entangled photons in the 1.5-micron telecom band when the fiber is pumped at 775 nm. A greater-than 80:1 coincidence-to-accidental ratio is achieved, limited mainly by multiphoton pair generation. Without the need to subtract accidentals or to compensate for walk-off, the raw two-photon interference visibility is found to be better than 95%, and violation of Bell's inequality is observed by more than 18 standard deviations. This makes for a truly alignment-free, plug-and-play source of polarization-entangled photon pairs.