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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Demonstration of an active quantum key distribution network

Xiao Hong Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Xu Hai, Barry Hershman, Joshua C. Bienfang, David Su, Ronald F. Boisvert, Charles W. Clark, Carl J. Williams

Published Aug 31, 2006• 18 citations
Publisher

Abstract

We previously demonstrated a high speed, point to point, quantum key distribution (QKD) system with polarization coding over a fiber link, in which the resulting cryptographic keys were used for one-time pad encryption of real time video signals. In this work, we extend the technology to a three-node active QKD network - one Alice and two Bobs. A QKD network allows multiple users to generate and share secure quantum keys. In comparison with a passive QKD network, nodes in an active network can actively select a destination as a communication partner and therefore, its sifted-key rate can remain at a speed almost as high as that in the point-to-point QKD. We demonstrate our three-node QKD network in the context of a QKD secured real-time video surveillance system. In principle, the technologies for the three-node network are extendable to multi-node networks easily. In this paper, we report our experiments, including the techniques for timing alignment and polarization recovery during switching, and discuss the network architecture and its expandability to multi-node networks.

DOI
10.1117/12.679589

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We previously demonstrated a high speed, point to point, quantum key distribution (QKD) system with polarization coding over a fiber link, in which the resulting cryptographic keys were used for one-time pad encryption of real time video signals. In this work, we extend the technology to a three-node active QKD network - one Alice and two Bobs. A QKD network allows multiple users to generate and share secure quantum keys. In comparison with a passive QKD network, nodes in an active network can actively select a destination as a communication partner and therefore, its sifted-key rate can remain at a speed almost as high as that in the point-to-point QKD. We demonstrate our three-node QKD network in the context of a QKD secured real-time video surveillance system. In principle, the technologies for the three-node network are extendable to multi-node networks easily. In this paper, we report our experiments, including the techniques for timing alignment and polarization recovery during switching, and discuss the network architecture and its expandability to multi-node networks.
We demonstrate a three-node QKD network that allows multiple users to share secure keys. This QKD network operates on the 850 nm and 1550 nm wavelengths at 1.25 Gbps clock rate. The communication route is controlled by MEMS optical switches. In this paper, we report the network structure and experimental results including the performance of the optical switch, polarization recovery, and timing alignment technology during switching. This demonstration experimentally shows that QKD can be extended to active multi-node networks.
Abstract We report the implementation of a quantum key distribution (QKD) system over a three-user fiber-optic network in which each user employs an identical bidirectional transceiver, with a single asymmetric interferometer shared between the encoding and decoding paths to reduce duplicated optical resources at the node level. The three users-Alice, Bob, and Charlie-are interconnected through a passive circulator-based hub built from 3-port optical circulators, which enables secure key exchange between any pair of them without active switching or a trusted intermediary. Each user is connected to the central circulator via standard telecom fiber links of 10-15 km, resulting in effective inter-user distances of 20-25 km. We employed the BB84 protocol with a two-decoy-state method (weak and vacuum) for secure key generation. For each user pair, sifted keys of 10610^6106 bits were processed with a composable security parameter ε∼10−8\varepsilon \sim 10^{-8}ε∼10−8 . Secret key lengths were evaluated using three approaches: (1) theoretical estimation based on measured quantum bit error rate (QBER) and gains, assuming an error correction efficiency of 1.16; (2) experimental post-processing using Winnow; and (3) experimental post-processing using Cascade. All links achieved low QBERs and yielded positive secret key lengths. Cascade consistently produced longer final keys due to its higher reconciliation efficiency. These results demonstrate the feasibility of a resource-sharing bidirectional node architecture for secure multi-user quantum communication using passive circulator-based routing.
The National Institute of Standards and Technology (NIST) has developed a number of complete fiber-based high-speed quantum key distribution (QKD) systems that includes an 850 nm QKD system for a local area network (LAN), a 1310 nm QKD system for a metropolitan area network (MAN), and a 3-node quantum network controlled by a network manager. This paper discusses the key techniques used to implement these systems, which include polarization recovery, noise reduction, frequency up-conversion detection based on a periodically polled lithium nitrate (PPLN) waveguide, custom high-speed data handling boards and quantum network management. Using our quantum network, a QKD secured video surveillance application has been demonstrated. Our intention is to show the feasibility and sophistication of QKD systems based on current technology.
The quantum key distribution (QKD) method allows for the safe creation of encryption keys between trusted entities for secure communication. The suggested system is designed to enable secure communication between multiple parties (a single sender, Alice, and multiple receivers, Bobs) connected via a public channel susceptible to interception. It enables Alice to privately share encryption keys with each Bob over dedicated quantum channels, which can then be used to decrypt messages sent over the public network. The procedure involves Alice generating optical signals with randomly assigned properties such as intensity, phase, polarization, and frequencies. Alice randomly sends either signal states carrying information or decoy states with different frequencies to the receivers (Bobs) over the quantum channels. She also sends a synchronization signal for timing alignment with the quantum signals over the optical links. At the receiving end, the synchronization pulse timestamps the incoming quantum signals. Each Bob then randomly alters the frequencies of the received quantum signals and randomly measures their phase or polarization. The key is created from the frequency, phase, or polarization information of the quantum signals, resulting in longer keys. Key management agents manage the securely QKD-generated keys to encrypt information before sending it to the intended receivers. Essentially, this framework establishes authenticated, private communication by using QKD over dedicated ultra-secure quantum links to distribute decryption keys, ensuring that only intended users can access the content. The approach is designed to ensure end-to-end secure communication across the network.
We demonstrate a three-node active quantum key distribution (QKD) network with our previous two-way QKD system. An optical switch is used as a router to connect the two nodes. Adjacent nodes are connected by a 25 km optical fiber. The test over 11 h shows that our system can reduce the Raleigh backscattering efficiently in the absence of the storage fiber. Furthermore, the obtained average sifted key is about 1.2 kbps in the network, with high visibility and low quantum bit error rate in the long-time test.
Quantum key distribution (QKD) offers unconditional information security by allowing two distant users to establish a common encryption key resilient to hacking. Resultingly, QKD networks interconnecting critical infrastructure and enabling the secure exchange of classified information, can provide a solution to the increasing number of successful cyberattacks. To efficiently deploy quantum networks, the technology must be integrated over existing communication infrastructure, such as optical fibre links. Yet, QKD poses stringent requirements on the conditions of the network over which it is deployed. This work demonstrates the first quantum communication network in Cyprus via the deployment of a multi-node quantum network, exploiting existing commercial underground optical fibre. The network employs bidirectional occupation of fibres and wavelength multiplexing in a ring architecture to achieve, with minimal use of dark fibres, high-rate QKD. Results obtained reveal consistent key generation rates across all nodes, confirming reliable operation in a real-world environment. This deployment highlights the feasibility of leveraging existing telecom infrastructure for quantum-secured communication, marking a significant step toward scalable and cost-effective quantum networks suited for critical applications.