Theory and experiment of entanglement in a quasi-phase-matched two-crystal source

Abstract

We report new results regarding a source of polarization entangled photon-pairs created by the process of spontaneous parametric downconversion in two orthogonally oriented, periodically poled, bulk KTiOPO4 crystals (PPKTP). The source emits light colinearly at the non-degenerate wavelengths of 810 nm and 1550 nm, and is optimized for single-mode optical fiber collection and long-distance quantum communication. The configuration favors long crystals, which promote a high photon-pair production rate at a narrow bandwidth, together with a high pair-probability in fibers. The quality of entanglement is limited by chromatic dispersion, which we analyze by determining the output state. We find that such a decoherence effect is strongly material dependent, providing for long crystals an upper bound on the visibility of the coincidence fringes of 41% for KTiOPO4, and zero for LiNbO3. The best obtained raw visibility, when canceling decoherence with an extra piece of crystal, was 91 \pm 0.2%, including background counts. We confirm by a violation of the CHSH-inequality (S = 2.679 \pm 0.004 at 55 s^{-1/2} standard deviations) and by complete quantum state tomography that the fibers carry high-quality entangled pairs at a maximum rate of 55 x 10^3 s^{-1}THz^{-1}mW^{-1}.

arXiv comment12 pages, 10 figures, REVTeX4

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Cited by in corpus (7)

• Entangled Photon-Pair Sources based on three-wave mixing in bulk crystals
• A high-brightness source of polarization-entangled photons optimized for applications in free space
• Modelling and optimization of photon pair sources based on spontaneous parametric down-conversion
• Compact source of narrow-band counterpropagating polarization-entangled photon pairs using a single dual-periodically poled crystal
• Extended Source of Indistinguishable Polarization-entangled Photons over Wide Angles of Emission
• Designing a compact cavity-enhanced source of entangled photons
• High-fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber