Abstract
The generation of two photon fields, to date, has been demonstrated utilizing a fully coherent pump beam. In this paper we demonstrate, the theoretical and experimental generation of polarization entangled single photon pairs by varying the spatial coherence of the pump beam. The effect of the pump beam spatial coherence on the visibility of a polarization-entangled single photon source is investigated. A comparison of the visibility measurements using a fully coherent and partially coherent pump beam is performed. It is shown that the partial coherence of the pump beam contributes to an increase in the visibility. The coherence properties of the beam are significant for free-space optical transmission in particular for long range free-space quantum communication.
Highlights
The process of spontaneous parametric down-conversion (SPDC)[1] is the foremost popular method of producing entangled photons and has acquired immense attention of late due to its potential applications in quantum communication especially for long range free-space and satellite quantum key distribution[2,3,4]
Non-collinear photon pairs at a down-converted wavelength of 810 nm were produced by two type-I Beta Barium Borate (BBO) crystals (7 × 7 × 0.7 mm) concatenated using a partially coherent pump beam laser lasing at 405 nm
The results of the experimental visibilities for the fully spatially coherent (FSC) and varying coherence lengths of partially spatially coherent (PSC) are presented in Table 1, including the corresponding theoretically calculated visibility attained from Equation (12)
Summary
The process of spontaneous parametric down-conversion (SPDC)[1] is the foremost popular method of producing entangled photons and has acquired immense attention of late due to its potential applications in quantum communication especially for long range free-space and satellite quantum key distribution[2,3,4]. The two-photon interference effect corresponding to temporal[12,8], spatial[13,14], and angular interference[15,16] has been demonstrated. The transfer of angular momentum of the pump beam[23] and the effect of the pump transverse width[19] on the down-converted photons have been investigated both theoretically and experimentally. In the present paper, applying the process of SPDC, we demonstrate a novel pump source for entangled photons by incorporating a scheme to produce partial spatial coherence of the pump beam. An experimental study is performed to investigate the effects of the pump spatial coherence, on the properties of the polarization-entangled photon field.
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