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arXiv:1506.04358 · Optics Letters

Highly efficient source for frequency-entangled photon pairs generated in a 3^rd-order periodically poled MgO-doped stoichiometric LiTaO_3 crystal

Heonoh Kim, Hee Jung Lee, Sang Min Lee, Han Seb Moon

Published Jun 19, 2015• 13 citations
arXivHTMLPDF

Abstract

We present a highly efficient source for discrete frequency-entangled photon pairs based on spontaneous parametric down-conversion using 3rd-order type-0 quasi-phase matching in a periodically poled MgO-doped stoichiometric LiTaO(3) crystal pumped by a 355.66-nm laser. Correlated two-photon states were generated with automatic conservation of energy and momentum in two given spatial modes. These states have a wide spectral range, even under small variations in crystal temperature, which consequently results in higher discreteness. Frequency entanglement was confirmed by measuring two-photon quantum interference fringes without any spectral filtering.

DOI
10.1364/ol.40.003061

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We present a highly efficient source for discrete frequency-entangled photon pairs based on spontaneous parametric down-conversion using 3rd-order type-0 quasi-phase matching in a periodically poled MgO-doped stoichiometric LiTaO(3) crystal pumped by a 355.66-nm laser. Correlated two-photon states were generated with automatic conservation of energy and momentum in two given spatial modes. These states have a wide spectral range, even under small variations in crystal temperature, which consequently results in higher discreteness. Frequency entanglement was confirmed by measuring two-photon quantum interference fringes without any spectral filtering.
We demonstrate a technique that generates frequency-entangled photon pairs with strong polarization correlation by using a single-period nonlinear crystal and single pass configuration. The technique is based on the simultaneous occurrence of two spontaneous parametric down-conversion processes satisfying independent type-II collinear quasi-phase matching conditions in periodically poled stoichiometric lithium tantalate. The generated photon pairs exhibit non-degenerate Hong-Ou-Mandel interference, indicating the presence of quantum entanglement in the frequency domain. This method provides a light source capable of wide-range quantum sensing and quantum imaging or high-dimensional quantum processing.
We study the spectral correlation of photon pairs generated via type-II spontaneous parametric down conversion in periodically poled lithium niobate crystals. By performing Schmidt decomposition on the two-photon wavefunction, we calculate the spectral purity of the two-photon state under various pump laser characteristics and doping concentrations of MgO in lithium niobate crystals. Our results show that periodically poled 5% MgO doped lithium niobate is a good candidate to generate photon-pairs with high spectral purity at telecom wavelength.
We demonstrate a technique that generates frequency-entangled photon pairs with high polarization definition by using a single-period nonlinear crystal and single pass configuration. The technique is based on the simultaneous occurrence of two spontaneous parametric down-conversion processes satisfying independent type-II collinear pseudo-phase matching conditions in periodically poled stoichiometric lithium tantalate. The generated photon pairs exhibit non-degenerate Hong-Ou-Mandel interference, indicating the presence of quantum entanglement in the frequency domain. This method provides a light source capable of wide-range quantum sensing and quantum imaging or high-dimensional quantum processing.
We report a simple scheme for direct generation of frequency-bin entangled photon pairs via spontaneous parametric downconversion. Our fabricated nonlinear optical crystal with two different poling periods can simultaneously satisfy two different, spectrally symmetric nondegenerate quasi-phase-matching conditions, enabling the direct generation of entanglement in two discrete frequency-bin modes. Our produced photon pairs exhibited Hong-Ou-Mandel interference with high-visibility beating oscillations- a signature of two-mode frequency-bin entanglement. Moreover, we demonstrate deterministic entanglement-mode conversion from frequency-bin to polarization modes, with which our source can be more versatile for various quantum applications. Our scheme can be extended to direct generation of high-dimensional frequency-bin entanglement, and thus will be a key technology for frequency-multiplexed optical quantum information processing.
Entangled photon pairs have attracted many interests from the view of quantum science and technologies. However, there are still several technical issues remaining in the conventional generation method, such as complexity and inefficiency. Here we propose a simple scheme to generate frequency-entangled photon pairs via spontaneous parametric down-conversion in periodically poled stoichiometric lithium tantalite. Our method will open a way to construct a compact and efficient source of entangled photons for quantum sensing.
Ultrabright sources of entangled photon pairs with high heralding efficiency are an important step in the pursuit of high-bit-rate entanglement-base quantum key distribution, as well as an enabling tool for loss-sensitive quantum optics experiments. Here, we present a robust single-mode fiber-coupled source of polarization-entangled photons around 810 nm with both high brightness and heralding efficiency. Our approach is based on quasi-phase-matched spontaneous parametric downconversion (SPDC) from periodically poled KTiOPO4 in a Sagnac loop configuration. We demonstrate a high degree of two-photon polarization entanglement for single-frequency-pumped type-0 and type-II SPDC, and conduct a conclusive comparison in terms of efficiency and spectral characteristics. In light of applications outside a laboratory environment, we evaluate the feasibility of pumping nonlinear crystals with free-running laser diodes.