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Optics Express

Non-degenerated sequential time-bin entanglement generation using periodically poled KTP waveguide

Lijun Ma, Oliver Slattery, Tiejun Chang, Xiao Hong Tang

Published Aug 21, 2009• 30 citations
Publisher

Abstract

We have experimentally implemented a non-degenerate sequential time-bin entangled photon-pair source using a periodically poled potassium titanyl phosphate waveguide at a clock rate of 1 GHz. The wavelengths of the signal and idler are 895 nm and 1310 nm, which are suitable for local and long distance optical communications, respectively and the 895 nm signal is also suitable for quantum memory research. A silicon avalanche photodiode is used to detect the photons at 895 nm while a periodically poled lithium niobate waveguide based up-conversion detector is used to detect the photons at 1310 nm. The measured entangled-photon-pair flux rate is 650 Hz and the fringe visibility for two-photon interference is 79.4% without noise subtraction.

DOI
10.1364/oe.17.015799

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We have experimentally implemented a non-degenerate sequential time-bin entangled photon-pair source using a periodically poled potassium titanyl phosphate waveguide at a clock rate of 1 GHz. The wavelengths of the signal and idler are 895 nm and 1310 nm, which are suitable for local and long distance optical communications, respectively and the 895 nm signal is also suitable for quantum memory research. A silicon avalanche photodiode is used to detect the photons at 895 nm while a periodically poled lithium niobate waveguide based up-conversion detector is used to detect the photons at 1310 nm. The measured entangled-photon-pair flux rate is 650 Hz and the fringe visibility for two-photon interference is 79.4% without noise subtraction.
We report an experimental demonstration of the distribution of time-bin entangled photon pairs over 100 km of optical fiber. In our experiment, 1.5-mum non-degenerated time-bin entangled photon pairs were generated with a periodically poled lithium niobate (PPLN) waveguide by using the parametric down conversion process. Combining this approach with ultra-low-loss filters to eliminate the pump light and separate signal and idler photons, we obtained an efficient entangled photon pair source. To detect the photons, we used single-photon detectors based on frequency up-conversion. These detectors operated in a non-gated mode so that we could use a pulse stream of time correlated entangled photon pairs at a high repetition frequency (1 GHz). Using these elements, we distributed time-bin entangled photon pairs over 100 km of dispersion shifted fiber and performed a two-photon interference experiment. We obtained a coincidence fringe of 81.6% visibility without subtracting any background noise, such as accidental coincidence or dark count, which was good enough to violate Bell's inequality. Thus, we successfully distributed time-bin entangled photon pairs over 100 km.
Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mum pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides. We report what we believe to be a new method using cascaded second-order nonlinearity in a single PPLN waveguide to produce high-purity time-bin entangled photon pairs. We confirmed the generation of entanglement through a two-photon interference experiment showing a coincidence fringe with a visibility of up to 97%.
Photon pair sources in the visible to NIR wavelength region play a key role in quantum optics. The wavelength range around 800 nm provides an opportunity for using low cost detectors, which makes it highly interesting for practical, large scale quantum applications. Here, we report on the realization of single mode Rubidium (Rb) exchanged waveguides in periodically poled (PP) Potassium Titanyl Phosphate (Rb:KTiOPO4 or Rb:KTP) for frequency-non-degenerate type II parametric down-conversion pumped at 400 nm and generating pairs of photons at around 800 nm. The source exhibits a nonlinear conversion efficiency of 2.0%/(Wcm2), estimated from SHG measurements. Characterisation of the generated two-photon state confirms nonclassical photon-number correlations, characterized by g(1,1). The high nonlinear conversion efficiency and low temperature sensitivity make this source a promising candidate for operations in both classical and quantum integrated network applications.