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Asia Communications and Photonics Conference

Towards the Quantum Internet: Prospects and Challenges of Efficient Entanglement Distribution Over Telecom Fibers

Matheus Ribeiro Sena, Mael Flament, Mehdi Namazi, Shane Andrewski, G. Di Bello, Ralf-Peter Braun, Marwa Youssef-Sayed, Ronny Döring, Michaela Ritter, Ming Yin, Oliver Holschke, Marc Geitz

Published Nov 2, 2024• 0 citations
Publisher

Abstract

Network operators hold a significant asset in their widespread optical fiber networks and as quantum technologies advance, these operators will be ideally positioned to offer new streams of services in the context of the Quantum Internet. However, establishing a functional Quantum Internet requires diverse technological advancements, particularly in the efficient distribution of entanglement over optical fibers. Entanglement serves as the cornerstone for quantum protocols and technologies such as quantum repeaters, teleportation, sensing, and time synchronization. Nonetheless, as photons propagate through fiber, they encounter various impairments that can degrade entanglement quality. Specifically, polarization-entangled photons suffer from polarization drifts, which exhibit stochastic behavior and can reduce fidelity. In this paper, we examine the prospects of entanglement distribution for the Quantum Internet, presenting experimental campaigns that highlight both the challenges and solutions. We demonstrate the inherent instability of photon fidelity in field-deployed fibers and show how compensation schemes can effectively enhance entanglement transmission in urban fiber networks. Our findings include results from a four-day entanglement distribution experiment conducted over Deutsche Telekom's optical fiber network in Berlin, achieving an average Bell parameter and fidelity of 2.52 and 99.6%, respectively.

DOI
10.1109/acp/ipoc63121.2024.10809958

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Network operators hold a significant asset in their widespread optical fiber networks and as quantum technologies advance, these operators will be ideally positioned to offer new streams of services in the context of the Quantum Internet. However, establishing a functional Quantum Internet requires diverse technological advancements, particularly in the efficient distribution of entanglement over optical fibers. Entanglement serves as the cornerstone for quantum protocols and technologies such as quantum repeaters, teleportation, sensing, and time synchronization. Nonetheless, as photons propagate through fiber, they encounter various impairments that can degrade entanglement quality. Specifically, polarization-entangled photons suffer from polarization drifts, which exhibit stochastic behavior and can reduce fidelity. In this paper, we examine the prospects of entanglement distribution for the Quantum Internet, presenting experimental campaigns that highlight both the challenges and solutions. We demonstrate the inherent instability of photon fidelity in field-deployed fibers and show how compensation schemes can effectively enhance entanglement transmission in urban fiber networks. Our findings include results from a four-day entanglement distribution experiment conducted over Deutsche Telekom's optical fiber network in Berlin, achieving an average Bell parameter and fidelity of 2.52 and 99.6%, respectively.
Entanglement distribution is a fundamental building block of quantum communication networks, enabling the secure and reliable exchange of quantum information over long distances. Unlike classical communication, quantum networks exploit the unique properties of quantum entanglement to support applications such as quantum key distribution, quantum teleportation, distributed quantum computing, and networked quantum sensing. Although significant progress has been made in recent years, the efficient generation, transmission, and preservation of entangled states remain major research challenges due to photon loss, decoherence, and limitations in current communication infrastructure.This review provides a comprehensive overview of entanglement distribution in quantum communication networks, focusing on the technologies that enable practical implementation and the latest experimental developments. It discusses key approaches for generating and distributing entangled photons through optical fibers, free-space links, and satellite-based communication, together with supporting technologies such as quantum repeaters, quantum memories, and photonic devices. The review also examines recent experimental demonstrations that have advanced long-distance quantum communication while highlighting the technical barriers that must be overcome for large-scale deployment. Finally, emerging applications and future research directions are presented, including the development of scalable quantum networks, the quantum internet, and secure global communication systems. This review aims to provide researchers and students with a clear understanding of the current state of entanglement distribution and its growing role in next-generation quantum communication technologies.
Distributing quantum entanglement over telecommunication fiber is a fundamental task in metropolitan-scale quantum networks, enabling advanced applications such as quantum-secured communication, quantum sensing, and distributed quantum computing. Although polarization entanglement is relatively easy to generate and manipulate, its distribution across deployed fibers is challenging because of the time-varying polarization transformations imposed by the fiber, which must be actively stabilized. In this work, we experimentally demonstrate the distribution of polarization-entangled photons over a 62 km, partially aerial fiber between the National Institute of Standards and Technology and the University of Maryland. With polarization stabilization applied to the fiber, we achieved a photon pair rate of approximately 1500s −1 and observed a time-averaged CHSH inequality parameter of S =2.34±0.37. During a continuous 24 h experiment, time-multiplexed polarization compensation sessions only cost 7.2% of the total link operation time, leaving an entanglement distribution uptime of 92.8%. Our results demonstrate the feasibility of distributing polarization-entangled photons over challenging fiber conditions, which is an important step toward the practical deployment of quantum networks.
Entanglement distribution between spatially distant nodes is crucial for advancing the development of quantum networks. Achieving large-scale, practical quantum networks by leveraging existing fiber infrastructures and commercial technologies can greatly enhance cost efficiency in real-world applications. As such, the simultaneous transmission of quantum entanglement and classical signals within a single optical fiber is becoming increasingly desirable, yet it remains challenging due to the substantial intensity disparities between single-photon-level quantum light and classical traffic. In this study, we theoretically describe and experimentally implement polarization entanglement distribution using a continuous wave pumped integrated AlGaAs Bragg reflection waveguide quantum source, coexisting with classical light in optical fiber at the telecom C-band. The characteristics of noise photons are analyzed and evaluated under different levels of classical light power. Using the BBM92 protocol for quantum key distribution, we demonstrate that temporal and spectral filtering during coincidence detection, combined with optimized source brightness, effectively influences the secure key rate and achievable distance of the system. Polarization drift is measured across various fiber paths, with 35-hour stability tests on fibers ranging up to 55 km in length. Our results can guide the initial design of optimal entanglement distribution networks that are compatible with fiber-optic communication systems.
The coming Quantum Internet will bring us new capabilities: advanced cryptographic functions, high-precision sensor networks for uses such as high-resolution astronomy, and secure distributed quantum computing. Experimental progress on the components for quantum repeaters is moving at a dizzying rate, and theorists have proposed various approaches to managing errors to create high-fidelity quantum entanglement. Building quantum networks presents different challenges from building quantum links. I will give an overview of these issues, then discuss the even more daunting challenge of creating a network of networks -- an internetwork -- and show how our simulations are guiding the design of a true quantum Internet. These challenges include routing (path selection), resource management such as multiplexing techniques, and security considerations within individual networks. Recently, we have discovered that it is possible for a single hijacked quantum repeater to frame other repeaters as malicious, substantially disrupting network operations. All of these issues are magnified when discussing autonomous networks that exchange information, known as an internetwork. In internetworking, not only is the scale of the problem daunting, but heterogeneous technologies will be deployed and demand interoperability at the logical level as well as the physical. Network operators also prefer to maintain the privacy of their own network operations, requiring mechanisms including connection establishment to operate with minimal sharing of information across network boundaries.
Optical photons play unique role in transmitting information over long distances. Photonic links by the optical fiber networks compose the backbone of today's global internet. Such fiber optics can also provide the most cost-effective quantum channels to distribute quantum information across distant stationary nodes in future large-scale quantum networks. This prospect motivates the recent emerging efforts in developing microwave-optical quantum transduction technology to interconnect microwave quantum processors. Various frequency conversion approaches are investigated to efficiently bridge the enormous electromagnetic frequency gap while preserving quantum coherence. Nonetheless, high-fidelity entanglement generation between remote quantum processing units has remained out of reach to date. Here, we summarize the state-of-the-art progresses in quantum transducer engineering and provide the perspectives on the key challenges and opportunities toward optically heralded quantum entanglement distributions.
Quantum communication, our ability to transmission quantum information between remote locations, is a primitive operation necessary for any future quantum internet. At its heart quantum communication relies on establishing entangled links between remote locations which can then be used to teleport quantum data. The ultimate performance of such approaches is limited by photon losses in the optical fiber channels. We introduce the concept of quantum multiplexing, which allows us to both minimize the number of photons needed in the entanglement distribution processing while at the same time enhancing the quality of the entangled pairs generated. Our approach should improve the performance of quantum communication systems and repeater networks. © 2019 The Author(s)