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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Compact sources of correlated and entangled photons

Marco Fiorentino B, S. M. Spillane, Tony Roberts, Raymond G. Beausoleil

Published Sep 11, 2007• 1 citation
Publisher

Abstract

We present two experiments geared toward the realization of a robust and intense source of polarization-entangled photons. First, we describe a novel source of polarization-entangled pairs that uses periodically-poled potassium titanyl phosphate (PPKTP) and an interferometer based on polarization beam displacers. The source emits an intense flux of high-quality single-mode entangled photons and is stable, robust, and easy to align. Second, we report on sources of correlated photons generated in PPKTP waveguides. Waveguide sources of correlated pairs have been shown to generate high fluxes of pairs: we theoretically and experimentally investigate spontaneous parametric down-conversion generation of photon pairs in waveguides at different wavelengths.

DOI
10.1117/12.730526

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We present two experiments geared toward the realization of a robust and intense source of polarization-entangled photons. First, we describe a novel source of polarization-entangled pairs that uses periodically-poled potassium titanyl phosphate (PPKTP) and an interferometer based on polarization beam displacers. The source emits an intense flux of high-quality single-mode entangled photons and is stable, robust, and easy to align. Second, we report on sources of correlated photons generated in PPKTP waveguides. Waveguide sources of correlated pairs have been shown to generate high fluxes of pairs: we theoretically and experimentally investigate spontaneous parametric down-conversion generation of photon pairs in waveguides at different wavelengths.
We experimentally demonstrate a source of polarization entangled photon-pairs based on a single periodically poled potassium titanyl phosphate crystal pumped with a broadband, free running laser diode. The crystal is placed within a linear beam-displacement interferometer and emits photon-pairs based on type-0 spontaneous parametric downconversion. We observe pair rates of 0.56 Mpairs/s/mW in a single spatial mode with a polarization visibility of 97.7% over a spectral range of 100 nm. This experiment demonstrates a pathway toward observing gigacount rates of polarization entangled photon pairs by using high-power free-running laser diodes with fast multiplexed detectors.
We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in periodically poled potassium titanyl phosphate (PPKTP) waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. We use balanced non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements and investigate the power and spectral tunability of the system. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We built a separate platform containing a computer-controlled tomography system to characterize the produced states and another NPBS is installed to combine photons from adjacent waveguides and assess their interferability, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.
The need for bright efficient sources of entangled photons has been a subject of tremendous research over the last decade. Researchers have been working to increase the brightness and purity to help overcome the spontaneous nature of the sources. Periodic poling has been implemented to allow for the use of crystals that would not normally satisfy the phase matching conditions. Utilizing periodic poling and single mode waveguide confinement of the pump field has yielded extremely large effective nonlinearities in sources easily producing millions of photon pairs. Here we will demonstrate these large nonlinearity effects in a periodically poled potassium titanyl phosphate (PPKTP) waveguide as well as characterizing the source purity.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.