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Optics Express

Stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short PPLN waveguide

Han Chuen Lim, Akio Yoshizawa, Hidemi Tsuchida, Kazuro Kikuchi

Published Aug 4, 2008• 60 citations
Publisher

Abstract

We demonstrate a stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short periodically-poled lithium niobate (PPLN) waveguide. Full quantum state tomographic measurement performed on the photon-pairs has revealed a very high state purity of 0.94, and an entanglement fidelity exceeding 0.96 at the low-rate-regime. At higher rates, entanglement quality degrades due to emission of multiple-pairs. Using a new model, we have confirmed that the observed degradation is largely due to double- and triple-pair emissions.

DOI
10.1364/oe.16.012460

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We demonstrate a stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short periodically-poled lithium niobate (PPLN) waveguide. Full quantum state tomographic measurement performed on the photon-pairs has revealed a very high state purity of 0.94, and an entanglement fidelity exceeding 0.96 at the low-rate-regime. At higher rates, entanglement quality degrades due to emission of multiple-pairs. Using a new model, we have confirmed that the observed degradation is largely due to double- and triple-pair emissions.
Quantum entanglement is one of the most important resources for quantum communication, information and computing. Since active polarization stabilization methods could alleviate the polarization-drift problem over optical fibre, telecom-band polarization-entangled photon-pairs can be well distributed and shared. Spontaneous four-wave mixing in a dispersion-shifted fibre (DSF) can be used to realize a source of telecom-band polarization-entangled photon pairs, but DSF is often cooled to suppress noise photons generated by spontaneous Raman-scattering. Second-order nonlinear crystals or waveguides such as periodically-poled lithium niobate (PPLN) waveguides are also available and generation has been reported on the conditions of careful selection of two nearly identical nonlinear crystals or accurate temperature-control of waveguides.
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%.
In this paper, we present a compact source of narrow-band energy–time-entangled photon pairs in the telecom regime based on a Ti-indiffused periodically poled lithium niobate (PPLN) waveguide resonator, i.e. a waveguide with end-face dielectric multi-layer mirrors. This is a monolithic doubly resonant optical parametric oscillator (OPO) far below threshold, which generates photon pairs by spontaneous parametric down-conversion (SPDC) at around 1560 nm with a 117 MHz (0.91 pm)-bandwidth. A coherence time of 2.7 ns is estimated by a time correlation measurement and a high quality of the entangled states is confirmed by a Bell-type experiment. Since highly coherent energy–time-entangled photon pairs in the telecom regime are suitable for long distance transmission and manipulation, this source is well suited to the requirements of quantum communication.