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International Conference on Quantum Communications, Networking, and Computing (QCNC)

Testbed and Experiments for Quantum-Conventional Networking

Nageswara S. V. Rao, Muneer Alshowkan, Joseph C. Chapman, Hsuan‐Hao Lu, Nicholas A. Peters, Joseph M. Lukens, Guoliang Xue, Saikat Guha, Emily A. Van Milligen, Don Towsley, Gayane Vardoyan, Leonardo Bacciottini, Linran Fan

Published Mar 31, 2025• 3 citations
Publisher

Abstract

The realization of quantum networks requires the development of devices and methods unprecedented in conventional networks, and yet they critically depend on the latter for implementing foundational blocks and essential operations. We describe a testbed to support the development and testing of their functionality and performance by providing quantum and conventional data planes and devices, together with a secure conventional control plane. It incorporates a variety of entangled photon sources, qubit technologies, detector technologies, photonic components, and supporting conventional switches and workstations. It implements a novel fiber telescoping scheme that provides suites of connections using fiber spools and inground-aerial fiber loops. We briefly summarize a variety of experiments conducted over this testbed including: (i) flex-grid quantum connection experiments, (ii) quantum state and channel tomography, (iii) utilization of quantum key distribution keys to secure conventional encryption and firewall devices, (iv) comparative study of analytical capacity estimates and entanglement throughput, (v) deployed squeezing coexisting with conventional communications, and (iv) measurement of polarization time variation.

DOI
10.1109/qcnc64685.2025.00031

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The realization of quantum networks requires the development of devices and methods unprecedented in conventional networks, and yet they critically depend on the latter for implementing foundational blocks and essential operations. We describe a testbed to support the development and testing of their functionality and performance by providing quantum and conventional data planes and devices, together with a secure conventional control plane. It incorporates a variety of entangled photon sources, qubit technologies, detector technologies, photonic components, and supporting conventional switches and workstations. It implements a novel fiber telescoping scheme that provides suites of connections using fiber spools and inground-aerial fiber loops. We briefly summarize a variety of experiments conducted over this testbed including: (i) flex-grid quantum connection experiments, (ii) quantum state and channel tomography, (iii) utilization of quantum key distribution keys to secure conventional encryption and firewall devices, (iv) comparative study of analytical capacity estimates and entanglement throughput, (v) deployed squeezing coexisting with conventional communications, and (iv) measurement of polarization time variation.
Secure communication is essential for modern society, from financial transactions to critical infrastructure. As classical encryption faces threats from advancing computational power, quantum communication provides a fundamentally secure alternative based on physical laws. We present QuaNTUM (Quantum Network at the Technical University of Munich), a modular and extensible quantum communication testbed enabling scalable experiments across fiber-based campus networks and satellite-ground links. The terrestrial network connects research institutions in Garching near Munich via single-mode fibers in a star topology with polarization-maintaining components, multiplexers, and time-synchronized analysis modules. Active polarization control and real-time feedback support stable qubit transmission for high-fidelity quantum key distribution and entanglement distribution. A key feature is the integration of deterministic solid-state single-photon sources, including defects in hexagonal boron nitride and excited erbium atoms, with initial deployments on small satellites to bridge terrestrial and free-space channels. As an open-access platform, QuaNTUM enables protocol development, device benchmarking, and hybrid network research, providing a foundation for scalable quantum communication and future global quantum networks.
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Quantum networks provide a versatile infrastructure for communication, computing, and sensing with quantum information. Novel sources and detectors for transmitting and receiving quantum states are critical elements in the development and eventual deployment of robust quantum networks. Alongside performance, the compatibility of quantum network devices with modern networking infrastructure is an important requirement for deployment. We present results on the integration of quantum communication using superdense coding transmitted over optical fiber links into network environments. Our approach takes advantage of a novel complete Bell-state measurement setup that relies on hyper-entanglement in the temporal and polarization degrees of freedom for a two-photon state emitted from a quantum light source. Using linear optics and common single-photon detectors, we record a single-qubit channel capacity of 1.665±0.018. We then demonstrate a full experimental implementation of hybrid, quantum-classical communication protocol for image transfer applications. Our devices integrate with existing fiber optical network and software-defined transmitters and receivers as part of a modular design to provide an extensible quantum communication system that can adapt to future quantum technology goals.
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Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users [1] and our work scaling the network to a complete end to end metropolitan quantum network with 8 users [2] . Our network architecture optimises the resources required by each user without sacrificing security or functionality. We established several long-distance loopback connections and demonstrated extended stable operation with high secure key rates. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive. Further, we present our efforts towards coexistence of 100 Gbps classical communication and all quantum channels used in the network over the same deployed optical fibres.
The throughput of entangled qubit pairs per second (eqps) is a basic performance metric of quantum networks with entanglement distribution capability. It is measured over a fiber connection using specialized instruments, including photonic entanglement sources and single-photon detectors. Extensive theory has been developed to estimate the capacity of a generic quantum channel, which in turn is applied to estimate the maximum achievable eqps over a fiber connection. However, there is a gap in relating these two characterizations of entanglement distribution performance, in part due to the disparate nature of mathematical formulae of the channel capacity and specialized instrumentation needed for eqps measurements. We describe eqps and related measurements collected over testbed connections of lengths up to 65 km composed of aerial-inground loops, fiber spools, and their hybrid compositions. We estimate the normalized capacity using the transmissivity parameter derived from single photon detector measurements. These estimates are then converted to bounds on eqps of the connection using the source eqps rate derived using co-located detector measurements. The results indicate a consistency between eqps measurements and their capacity estimates across all three types of fiber connections, and provide insights into relating the parameters of analytic capacity estimates to physical measurements.