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Acta Sinica Quantum Optica

Design of the Periodically Poled KTiOPO_4 Generating 852 and 1550 nm Bicolor Entangled Lights

Jiangrui Gao

Published Jan 1, 2011• 0 citations
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Abstract

In this paper,we theoretically design the second-order nonlinear periodically poled KTiOPO4 crystal(PPKTP) by the 0-type quasi phase matching of nonlinear coefficients d33.The period of PPKTP is 10.7 microns at 20 centigrade degree.The bicolor entanglement of 852 nm signal light and 1550 nm idle light can be generated when an optical parametric oscillator of the PPKTP is pumped by 550 nm light.One of entangled beams corresponds to Cs atomic transition line,the other corresponds to optical fiber communication wavelength.The entanglement is of importance for the quantum information network and atomic information storage.

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arXiv:2009.13321•Journal of the Optical Society of America B•Aug 19, 2020•10 citations
In this paper,we theoretically design the second-order nonlinear periodically poled KTiOPO4 crystal(PPKTP) by the 0-type quasi phase matching of nonlinear coefficients d33.The period of PPKTP is 10.7 microns at 20 centigrade degree.The bicolor entanglement of 852 nm signal light and 1550 nm idle light can be generated when an optical parametric oscillator of the PPKTP is pumped by 550 nm light.One of entangled beams corresponds to Cs atomic transition line,the other corresponds to optical fiber communication wavelength.The entanglement is of importance for the quantum information network and atomic information storage.
As important members of nonclassical states of light, squeezed states and entangled states are basic resources for realizing quantum measurements and constructing quantum information networks. We experimentally demonstrate that the two types of nonclassical optical states can be generated from an optical parametric oscillator (OPO) involving a periodically poled KTiOPO4 crystal with a domain-inversion period of 51.7 μm, by changing the polarization of the pump laser. When a vertically polarized 671 nm laser is used to pump the OPO, the intra-cavity frequency-down-conversion with type-0 quasi-phase matching is realized and the output optical beam is a quadrature amplitude squeezed state of light at the wavelength of 1342 nm with the fluctuation of quadrature component of 3.17 dB below the quantum noise limit (QNL). If the pump laser is horizontally polarized, the condition of the type-II quasi-phase matching is satisfied and the output optical beam becomes Einstein-Podolsky-Rosen entangled state of light with correlation variances of both quadrature amplitude-sum and quadrature phase-difference of 2.2 dB below the corresponding QNL.
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.
Entangled states are key resource for quantum information processing. In linear optics quantum computing，the most widely used entanglement resource is polarization entangled photon pairs generated via type-Ⅱ spontaneous parametric down-conversion. However，the brightness is not sufficient to perform quantum communication experiment between ground and satellite. In this paper we have developed a high-brightness entangled resource based on periodic polarization and quasi-phase marched periodically poled KTiOPO4 crystal. The number of generated entangled pairs is about 1.6×104s-1mW-1 and the visibility is 27∶1. Our source is with about one order of magnitude brighter than previous sources based on β-barium borate crystal. This leads to an immediate possibility for applications in the field of quantum key distribution，quantum teleportation and quantum computation. Particularly it would form a solid basis for future global quantum network.
We theoretically investigated spectrally uncorrelated biphotons generated in a counter-propagating spontaneous parametric downconversion (CP-SPDC) from periodically poled M T i O X O 4 ( M = K , Rb, Cs; X = P , As) crystals. By numerical calculation, it was found that the five crystals from the KTP family can be used to generate heralded single photons with high spectral purity and wide tunability. Under the type-0 phase-matching condition, the purity at 1550 nm was between 0.91 and 0.92, and the purity can be maintained over 0.90 from 1500 nm to 2000 nm wavelength. Under the type-II phase-matching condition, the purity at 1550 nm was 0.96, 0.97, 0.97, 0.98, and 0.98 for PPKTP, PPRTP, PPKTA, PPRTA, and PPCTA, respectively; furthermore, the purity can be kept over 0.96 for more than 600 nm wavelength range. We also simulated the Hong–Ou–Mandel interference between independent photon sources for PPRTP crystals at 1550 nm, and interference visibility was 92% (97%) under the type-0 (type-II) phase-matching condition. This study may provide spectrally pure narrowband single-photon sources for quantum memories and quantum networks at telecom wavelengths.