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Journal of Applied Physics

Generation of frequency tunable polarization entangled photon pairs

Atsushi Yabushita, Takayoshi Kobayashi

Published Mar 15, 2006• 9 citations
Publisher

Abstract

Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency resolved photons was measured under several typical configurations. By optimizing a condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation.

DOI
10.1063/1.2183355

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Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency resolved photons was measured under several typical configurations. By optimizing a condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation.
Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency-resolved photons was measured under several typical configurations. By optimizing the condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation.
Quantum computation and quantum communication require sources of entangled photons, especially from low-cost diode lasers. This study considered a polarization entangled photons pulse source produced via a spontaneous parametric down-conversion process in the type-I phase-matching of two nonlinear crystals, incorporating a continuous wave laser diode operating in pulse mode as a pump. The generated photons were measured based on visibility as a function of the pump frequency and collection apertures. A polarization correlation between photon pairs of approximately 93% and a Bell parameter S value of 2.56 ± 0.05 were obtained using the source described here.
Polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum communications, quantum computation and high precision quantum metrology. We report on the generation of a continuous-wave pumped 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II periodically poled KTiOPO(4) (PPKTP) crystal in a Sagnac interferometer. Hong-Ou-Mandel (HOM) interference measurement yields signal and idler photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The source can be tuned over a broad range against temperature or pump power without loss of visibilities. This source will be used in our future experiments such as generation of orbital angular momentum entangled source at telecom wavelength for quantum frequency up-conversion, entanglement based quantum key distributions and many other quantum optics experiments at telecom wavelengths.
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.
Polarization-entangled photon pairs have been widely used as a light source for quantum communication. The polarization-entangled photon pairs are generally obtained at the crossing points of the light cones that are generated from a type-II nonlinear crystal. However, it is hard to pick up the photon pairs coming out from the crossing points because of their invisible wavelength and low intensity. In our previous work, we succeeded in generating polarization-entangled photon pairs by overlapping two light paths for the photon-pair generation. The photon pairs could be entangled in all of the generated photon pairs without clipping the crossing points, even with some difficulty in their alignment to overlap the two light paths. In this paper, we have developed an optical system that generates polarization-entangled photon pairs using a beamlike photon pair, without the difficulty in alignment. The measured results show that the photon pairs generated in the system are entangled in their polarizations.