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Journal of the Optical Society of America B

Femtosecond source of unbalanced polarization-entangled photons

Milrian S. Mendes, Lenin Fernández, A. S. Coelho, Marcio H. G. de Miranda, Fernando Parisio, Marco Bellini, D. Felinto, K. N. Cassemiro

Published Jul 16, 2015• 3 citations
Publisher

Abstract

We characterize a polarization-entangled photon source based on femtosecond pulsed parametric downconversion in a periodically poled χ(2) medium. Employing a Sagnac interferometer, we prepared different quantum states aiming at future investigations in quantum information and on the foundations of quantum mechanics. In this work we demonstrate the controlled generation of unbalanced entangled states, rather than the usual maximally entangled ones, by tuning the polarization of the system’s pumping field.

DOI
10.1364/josab.32.001670

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We characterize a polarization-entangled photon source based on femtosecond pulsed parametric downconversion in a periodically poled χ(2) medium. Employing a Sagnac interferometer, we prepared different quantum states aiming at future investigations in quantum information and on the foundations of quantum mechanics. In this work we demonstrate the controlled generation of unbalanced entangled states, rather than the usual maximally entangled ones, by tuning the polarization of the system’s pumping field.
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Photonic quantum information experiments demand bright and highly entangled photon pair sources. The combination of periodic poling and collinear excitation geometry allows the use of considerably longer crystals for parametric down-conversion. We demonstrate a picosecond-pulsed laser pumped source of high quality polarization entangled photon pairs. The phase of the output biphoton state is affected by the relative phase of the two-color interferometer and the phase of the nonlinearly interacting Gaussian beams. We measure the influence of these onto the phase of the output state. The presented source is a promising candidate for a compact, semiconductor laser driven source of entangled photon pairs.
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This thesis describes the design, development, and implementation of a pulsed source of polarization-entangled photons using spontaneous parametric down-conversion in a Sagnac interferometer. A tangle of 0.9286 ± 0.0015, fidelity to the state (|10〉 + |01〉)/√2 of \n0.9798 ± 0.0004 and a brightness of 597 pairs/s/mW were demonstrated. \n \nSpontaneous parametric down-conversion is a nonlinear optical process in which one photon is split into two lower-frequency photons while conserving momentum and energy, in this \nexperiment nearly degenerate photons are produced. These photons are then interfered at the output beamsplitter of the interferometer, exchanging path entanglement for polarization entanglement and generating the desired polarization-entangled photon pairs.
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.