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Quantum 2.0 Conference and Exhibition

A Cost-effective and Plug-and-play Entangled Biphoton Source for Quantum Networks

Rong Xue, Christopher J. Chunnilall

Published Jan 1, 2025• 0 citations
Publisher

Abstract

A cost-effective, plug-and-play, fiber-based quantum entanglement source based on a single periodically poled lithium niobate (PPLN) waveguide with a reflection scheme was developed, generating energy-time or time-bin entangled photon pairs in the telecom C-band.
DOI
10.1364/quantum.2025.qth3a.15

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A quantum entanglement source distributing entangled photons to multiple users is an indispensable component of a quantum network. Furthermore, the development of affordable and easy-to-use entanglement sources can pave the way for widespread deployment of quantum networks. Here, a cost-effective, rack-mountable, fiber-based entanglement source in the telecom band has been developed. Based on second-order nonlinear optical processes in one periodically poled lithium niobate waveguide utilizing a reflection scheme, the source exhibited good signal-to-noise characteristics at high photon pair generation rates with a broadband spectrum covering the entire C-band and parts of the S-band and L-band. Three different wavelength-correlated energy-time and time-bin entangled photon pairs were demonstrated, whose entanglement properties were verified by measuring interference fringes with visibilities exceeding 96.5% for energy-time entanglement and 91.1% for time-bin entanglement. This source has great potential for implementing practical quantum networks and other scenarios.
A fully fibered source of entangled photon pairs based on a nonlinear Sagnac interferometer is reported. Operating at telecom wavelengths, the source relies exclusively on standard fiber-optic components and periodically poled lithium niobate (PPLN) waveguides, resulting in a compact, robust, and field-deployable architecture. The generation stage supports both polarization and energy-time entanglement without modification, enabling versatile operation depending on the targeted application. Broadband spontaneous parametric down-conversion allows dense wavelength-division multiplexing over the telecom C and L bands. High normalized brightness (10.3 kpairs/s/nm/mW2^22) is achieved on a standard 100 GHz ITU channel pair, together with high entanglement quality. Polarization and energy-time encodings are characterized through state tomography and two-photon interference measurements, yielding fidelities, purities, and visibilities exceeding 96 % over multiple wavelength channels. The stability and reproducibility of the source are further evaluated through long-duration operation in a network environment. These results demonstrate that the proposed Sagnac source constitutes a practical and scalable building block for future plug-and-play quantum communication and quantum networking platforms.
Periodically poled lithium niobate waveguides (PPLN/W) are considered to be one of the most useful toolboxes for quantum communication experiments. Thanks to the high optical confinement over longer lengths than in bulk configurations (a few cm in our case), such structures provide highly efficient non-linear interactions, both in down- and up-conversion regimes. Within the framework of long-distance quantum communication at telecom wavelengths, PPLN/Ws have therefore been proved to be a key ingredient for building ultra-bright sources of energy-time, time-bin, as well as polarization entangled pairs of photons, up-conversion based detectors for telecom photon detection, photonic quantum interfaces for coherent wavelength conversion, and also for quantum relays in the entanglement swapping configuration.
We report a broadband energy-time entangled photon-pair source based on a fiber-pigtailed periodically poled lithium niobate (PPLN) waveguide, designed for applications in the quantum secure network.Utilizing the spontaneous parametric down-conversion nonlinear optical process, the source generates entangled photon pairs within a wavelength range of 64 nm in the telecom band at a pump wavelength of 770.3 nm.Photon pairs from eight paired International Telecommunication Union (ITU) channels are selected, and their correlation and entanglement properties are characterized.The measured coincidence counts of photon pairs from eight paired ITU channels are larger than 152.9 kHz when the coincidence-to-accidental ratios are greater than 260.Entanglement properties are measured through two-photon interference in the Franson interferometer, with all visibilities of interference curves exceeding 98.13%.Our demonstration provides a broadband energy-time entangled photon-pair source, contributing to the development of a large-scale quantum secure network.
We report the realization of a fiber-coupled time-bin entangled photon-pair source at 1538 nm. Unlike previous time-bin sources based on type-0 spontaneous parametric down conversion, our approach takes advantage of cross-polarized paired photons generated in a type-II periodically poled lithium niobate waveguide (PPLN/W). Here, we use a birefringent delay line (BDL) in a Michelson configuration to introduce a controllable delay between the paired photons. After the BDL, these photons are separated by a polarizing beam splitter (PBS) at 45° and sent to Alice and Bob. This way we create the non common time-bin entangled Bell state |Ψ ⟩ = 1/√2 [|s,l⟩ + |l,s⟩], where s and l represent the short and long time-bins, respectively.