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The European Physical Journal Special Topics

Flexible reconfigurable entanglement-based quantum key distribution network

Till Dolejsky, Erik Fitzke, Lucas Bialowons, Maximilian Tippmann, Oleg Nikiforov, Thomas Walther

Published Sep 12, 2023• 5 citations
Publisher

Abstract

Abstract Recently, we implemented a basic star-shaped entanglement-based quantum key distribution network without trusted nodes. It enables simultaneous pairwise exchange of quantum keys between multiple users. In this paper, we demonstrate its flexibility by focusing on several aspects. We show continuous system operation over a partially deployed 100 km fiber link for multiple days as well as dynamic reconfiguration of the communication partners. The photon pair source enables type-II or type-0 photon pair generation by SPDC as well as various demultiplexing strategies and repetition rates.

DOI
10.1140/epjs/s11734-023-00980-9

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Abstract Recently, we implemented a basic star-shaped entanglement-based quantum key distribution network without trusted nodes. It enables simultaneous pairwise exchange of quantum keys between multiple users. In this paper, we demonstrate its flexibility by focusing on several aspects. We show continuous system operation over a partially deployed 100 km fiber link for multiple days as well as dynamic reconfiguration of the communication partners. The photon pair source enables type-II or type-0 photon pair generation by SPDC as well as various demultiplexing strategies and repetition rates.
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We report on the design and field validation of a fully connected entanglement-based quantum key distribution (QKD) network employing a time-shared photon-pair source and reconfigurable optical switching. The system eliminates the need for trusted relay nodes and enables any-to-any secure connectivity among users over metropolitan-scale fiber infrastructure. We present a three-node prototype network operating in the O-band(1310/1316nm)(1310 / 1316 \text{nm})(1310/1316nm)which demonstrates key generation sufficient to provide pairwise 10 G encrypted connections between 32 users, and confirming practical feasibility for telecom integration.
The practical roll-out of quantum communication technologies in optical networks and the adoption of novel quantum applications demand the distribution of single or entangled photons. Flexibility and dynamicity are paramount for the provision of quantum resources, in order to scale with the number of users and to meet the demand of complex network architectures. We present a quantum network architecture that features this degree of reconfigurability, without being restricted to a rigid physical-layer network based on purely passive multiplexing componentry. We leverage spectral assets of photon-pair sources, from the short-wavelength band to the L-band, and agile spatial switching at a remote optical network node, in order to realize a flexible distribution map that features different flavors, reaching from cloud-centric to user-centric quantum connectivity. Photon pair distribution is experimentally demonstrated between five users in a 17-km reach, tree-shaped optical network, with high visibility entanglement shared between three users of the network. Simultaneous distribution of photons to more than one user is enabled and the delivered photon rate can be dynamically adjusted. Penalty-free operation is confirmed for integrating a co-existing classical control channel within the quantum.
Abstract Quantum key distribution (QKD) would play an important role in future information technologies due to its theoretically proven security based on the laws of quantum mechanics. How to realize QKDs among multiple users in an effective and simple way is crucial for its real applications in communication networks. In this work, we propose and demonstrate a fully connected QKD network without trusted node for a large number of users. Using flexible wavelength division multiplexing/demultiplexing and space division multiplexing, entanglement resources generated by a broadband energy-time entangled quantum light source are distributed to 40 users. Any two users share a part of entanglement resources, by which QKD is established between them. As a result, it realizes a fully connected network with 40 users and 780 QKD links. The performance of this network architecture is also discussed theoretically, showing its potential on developing quantum communication networks with large user numbers owing to its simplicity, scalability, and high efficiency.
Quantum communication is developed owing to the theoretically proven security of quantum mechanics, which may become the main technique in future information security. However, most studies and implementations are limited to two or several parties. Herein, we propose a fully connected quantum communication network without a trusted node for a large number of users. Using flexible wavelength demultiplex/multiplex and space multiplex technologies, 40 users are fully connected simultaneously without a trusted node by a broadband energy-time entangled photon pair source. This network architecture may be widely deployed in real scenarios such as companies, schools, and communities owing to its simplicity, scalability, and high efficiency.
Entanglement-based quantum links are the backbone of future quantum internet networks, enabling secure communication between distant cities. Realizing such networks requires addressing multiple practical challenges in long-distance quantum key distribution : time synchronisation, interferometer stabilisation and automation. Here, we report several advances. First, we maintained an operational QKD link continuously for 325hours over 50km between two remotes locations, demonstrating the feasibility of long-duration key generation. We further extended secure key distribution up to a 100km operational link connecting the University of Nice to a ground-based optical station, a setup compatible with future quantum satellite connections. Finally, by employing wavelength demultiplexing to separate photons of entangled pairs, we performed QKD across multiple ITU channels, achieving secure key exchange via the BBM92 protocol and time-energy observables.