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High-quality polarization entanglement engineering in standard telecom channels

Lutfi Arif Ngah, Florian Kaiser, Amandine Issautier, Harald Herrmann, W. Sohler, Anthony Martin, Sébastien Tanzilli

Published Jul 8, 2013• 0 citations
OpenAlex

Abstract

We report a compact, fully fibred approach for generating high-quality polarization entanglement in telecom C-band wavelength. The strength of our approach lies in the use of high-performance, standard fibre components to perform certain crucial tasks namely deterministic pair separation into two adjacent telecom ITU channels and temporal walk-off compensation between generated paired photons. We demonstrate the violation of the Bell's inequalities with more than 100 standard deviations.

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High-quality polarization entanglement engineering in standard ITU telecom channels

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•Jul 11, 2011•0 citations
We report a compact, fully fibred approach for generating high-quality polarization entanglement in telecom C-band wavelength. The strength of our approach lies in the use of high-performance, standard fibre components to perform certain crucial tasks namely deterministic pair separation into two adjacent telecom ITU channels and temporal walk-off compensation between generated paired photons. We demonstrate the violation of the Bell's inequalities with more than 100 standard deviations.
Recent advances in guided-wave optics bring quantum key distribution (QKD) to a new level where less complex, yet more robust, schemes have been proposed. Through continuous research in this field, newer QKD systems achieve higher bit rate, distance, and reliability. Entanglement-based QKD receives enormous attention from the scientific community, in order to increase the communication distance and to go to device-independent systems. In this framework, photons are generally the preferred qubit carrier, taking advantage of low-loss fibre optical networks, and high-performance standard telecom components. Future QKD networks will demand sources exhibiting high brightness, reliability, and photons in the standard telecom ITU channels for compatibility and easy integration with current technology. One of the most exploited approaches towards genera- ting photonic entanglement is based on the process of spontaneous parametric down-conversion (SPDC) in non-linear crystals. Usually employed entanglement observables are energy-time and polarization. The latter one is, without doubt, the easiest to analyze thanks to interferometer-free setups. Polarization entanglement is conveniently generated via the so-called type-II SPDC interaction, possibly in a waveguide non-linear structure for increasing the efficiency. Nevertheless, with a type-II source, there are some precautions that must be taken for achieving high entanglement qualities. In particular, the generated paired photons need to be spectrally and temporally indistinguishable. Typically, this requires spectral filtering, and temporal walk-off compensation stages. So far, these issues have been addressed by using bulk optics arrangements. We demonstrate a fully fibred approach based on a type-II periodically poled lithium niobate waveguide (PPLN/W) generating paired photons at 1540 nm (telecom C-band wavelength). We highlight the use of a standard polarization maintaining fibre (PMF) as an essentially loss-free, guided-wave solution to the temporal walk-off problem. By using standard telecom DWDMs, we perform, at the same time, the tasks of spectral filtering and deterministic photon pair separation in two ITU channels. By the violation of the Bell's inequalities with more than 100 standard deviations, we demonstrate excellent entanglement qualities and high coincidence rates. Our fully fibred approach offers very low losses, high reliability, and would be ready for QKD field tests.
We report a simple and practical approach for generating high-quality polarization entanglement in a fully guided-wave fashion. Both deterministic pair separation into two adjacent telecommunication channels and the paired photons' temporal walk-off compensation are achieved using standard fiber components. Two-photon interference experiments are performed, both for quantitatively demonstrating the relevance of our approach and for manipulating the produced state between bosonic and fermionic symmetries. The compactness, versatility and reliability of this configuration makes it a potential candidate for quantum communication applications.
Abstract Entanglement is a key resource in quantum information science and associated emerging technologies. Photonic systems offer a large range of exploitable entanglement degrees of freedom (DOF) such as frequency, time, polarization, and spatial modes. Hyperentangled photons exploit multiple DOF simultaneously to enhance the performance of quantum information protocols. Here, we report a fully guided-wave approach for generating polarization and energy-time hyperentangled photons at telecom wavelengths. Moreover, by demultiplexing the broadband emission spectrum of the source into five standard telecom channel pairs, we demonstrate compliance with fibre network standards and improve the effective bit rate capacity of the quantum channel up to one order of magnitude. In all channel pairs, we observe a violation of a generalised Bell inequality by more than 27 standard deviations, underlining the relevance of our approach.
We demonstrate high quality polarization entanglement at telecom wavelength, based on guided-wave technology. The fully fibered setup relies on a type-II periodically poled Lithium Niobate waveguide (PPLN/W) emitting pairs of cross-polarized photons (H,V) at 1310 nm. These photon pairs are sent onto a simple 50/50 fiber-optic coupler, leading to an entangled state of the form |Ψ>=(1/21/2)*(|Ha,Vb>+|Va,Hb>) in the coincidence basis, which is eventually distributed to "users" (a,b) through standard optical fibers. Along these distribution channels, the entangled state acquires an unknown phase between its two components leading to an "elliptically polarized" maximally entangled states |Ψ>=(1/21/2)*(| Ha,Vb>+eiφ|Va,Hb>), in which φ is a non random phase, and (a,b) represent the two channels at the output of the emitting source. For such a state, the usual settings used for optimal violation of the Bell inequality are no longer adapted. Thanks to the use of a phase compensator, namely a Soleil-Babinet birefringent system, we demonstrate experimentally that any phase can be compensated, leading to a maximal violation of the Bell inequality when the standard settings are used. Alternatively, we propose here a theoretical approach that allows, when applied to those particular states, determining the phase, and finding new analysis parameters towards optimizing the Bell inequality violation. After introducing our formalism in its generic form, we will show that it can be applied to several existing systems capable of either compensating or analyzing the phase.