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

Five-user QKD over switched fiber networks

Jan Bogdanski, Nima Rafiei, Mohamed Bourennane

Published Sep 5, 2008• 0 citations
Publisher

Abstract

Unconditionally secure multiuser quantum key distribution (QKD) over long distance switched telecom fiber networks will have a revolutionary impact on people's, companies', and governmental exchange of confidential information. We report five-user QKD over switched fiber networks in both star and tree configurations, using the BB84-protocol with phase encoding. Both setups implement polarization insensitive phase modulators, necessary for birefringent single mode fiber networks. In both configurations, for the mean photon number μ=0.1, we have achieved raw rates between 50Hz and 300Hz at distances between 25km to 50km with quantum bit error rates between 1.24% to 5.56%. The measurements have showed feasibility of multiuser QKD over switched telecom fiber networks, using standard fiber telecom components.

DOI
10.1117/12.798228

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arXiv:0901.4646•International Conference on Collaboration Technologies and Systems (CTS)•Jul 10, 2006•7 citations
Unconditionally secure multiuser quantum key distribution (QKD) over long distance switched telecom fiber networks will have a revolutionary impact on people's, companies', and governmental exchange of confidential information. We report five-user QKD over switched fiber networks in both star and tree configurations, using the BB84-protocol with phase encoding. Both setups implement polarization insensitive phase modulators, necessary for birefringent single mode fiber networks. In both configurations, for the mean photon number μ=0.1, we have achieved raw rates between 50Hz and 300Hz at distances between 25km to 50km with quantum bit error rates between 1.24% to 5.56%. The measurements have showed feasibility of multiuser QKD over switched telecom fiber networks, using standard fiber telecom components.
We are currently experiencing a rapid development of quantum information, a new branch of science, being an interdisciplinary of quantum physics, information theory, telecommunications, computer science, and many others. This new science branch was born in the middle of the eighties, developed rapidly during the nineties, and in the current decade has brought a technological breakthrough in creating secure quantum key distribution (QKD), quantum secret sharing, and exciting promises in diverse technological fields. Recent QKD experiments have achieved high rate QKD at 200 km distance in optical fiber. Significant QKD results have also been achieved in free-space. Due to the rapid broadband access deployment in many industrialized countries and the standing increasing transmission security treats, the natural development awaiting quantum communications, being a part of quantum information, is its migration into commercial switched telecom networks. Such a migration concerns both multiuser quantum key distribution and multiparty quantum secret sharing that have been the main goal of my PhD studies. They are also the main concern of the thesis. Our research efforts in multiuser QKD has led to a development of the five-user setup for transmissions over switched fiber networks in a star and in a tree configuration. We have achieved longer secure quantum information distances and implemented more nodes than other multi-user QKD experiments. The measurements have shown feasibility of multiuser QKD over switched fiber networks, using standard fiber telecom components. Since circular architecture networks are important parts of both intranets and the Internet, Sagnac QKD has also been a subject of our research efforts. The published experiments in this area have been very few and results were not encouraging, mainly due to the single mode fiber (SMF) birefringence. Our research has led to a development of a computer controlled birefringence compensation in Sagnac that open the door to both classical and quantum Sagnac applications. On the quantum secret sharing side, we have achieved the first quantum secret sharing experiment over telecom fiber in a five-party implementation using the "plug & play" setup and in a four-party implementation using Sagnac configuration. The setup measurements have shown feasibility and scalability of multiparty quantum communication over commercial telecom fiber networks.
We present the first Sagnac quantum secret sharing (in three- and four-party implementations) as well as Sagnac two-user quantum key distribution (QKD) over 1550 nm single mode fiber (SMF) networks, using the BB84- protocol with phase encoding. The secret sharing experiment has implemented a single qubit protocol, which allows for a practical secret sharing implementation over fiber telecom channels and in free-space. The previous quantum secret sharing proposals were based on multiparticle entangled states, not scalable and diffcult in the experimental implementations. Our experimental data show stable, in regards to birefringence drift, quantum secret sharing transmissions at the total Sagnac transmission loop distances of 45-55 km with the quantum bit error rates (QBER) of 3.0-3.7 % for the mean photon number μ = 0.1. In the QKD experiment we have achieved the total Sagnac transmission loop distances of 100-150 km with quantum bit error rates (QBER) of 5.84-9.79 % for μ = 0.1. The distances were much longer and rates much higher than in any other published Sagnac QKD experiments. The stability of quantum transmission in both secret sharing and QKD experiments has been achieved thanks to our new concept for compensation of SMF birefringence effects in Sagnac, based on a polarization control system and a polarization insensitive phase modulator. The measurement results have showed feasibility of quantum secret sharing and QKD over telecom fiber networks in Sagnac confi;guration, using standard fiber telecom components. Our birefringence compensation in SMF Sagnac open the door to other Sagnac-based applications over SMF links such as precise optical sensing, dispersion characteristics of optical fibers, acoustic and strain sensing, and generally sensing of any time varying phenomenon.
We present two long-distance quantum key distribution (QKD) systems over telecom fiber. The first one is the Sagnac QKD system implementing standard BB84 protocol. Novel polarization-insensitive phase modulators are used to simplify the conventional architecture. We are able to achieve a stable quantum bit error rate of 4-6.5% over 40km fiber loop over one hour without recalibration. The second one is the fiber-based QKD system using Gaussian-modulated coherent states. We have overcome the challenges imposed by the requirements for high detector sensitivity, long-term stability, and low signal crosstalk. Our GMCS QKD system is the first practical fiber-based one-way demonstration and is able to achieve a sifted secret key rate of 15.5 kbits/s over a transmission distance of 5km fiber. Experimental QKD is still in its infancy. The results presented in this thesis represent a significant step forward towards the practical QKD over conventional fiber networks.
A six-user quantum key distribution network implemented on a bus topology is experimentally demonstrated. The network employs the BB84 protocol to transmit cryptographic keys encoded unto the phase states of highly attenuated laser light to distances of up to 31 km in a standard telecommunication-grade fiber. Each user on the network is assigned a unique wavelength for communication with the network server at a time. The measured quantum bit error rate and sifted key rate compare favorably with theoretical results
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.
Quantum key distribution (QKD) has been developed within the last decade that is provably secure against arbitrary computing power, and even against quantum computer attacks. Now there is a strong need of research to exploit this technology in the existing communication networks. In this paper we have presented various experimental results pertaining to QKD like Raw key rate and Quantum bit error rate (QBER). We found these results over 25 km single mode optical fiber. The experimental setup implemented the enhanced version of BB84 QKD protocol. Based upon the results obtained, we have presented a network design which can be implemented for the realization of large scale QKD networks. Furthermore, several new ideas are presented and discussed to integrate the QKD technique in the classical communication networks.