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European Quantum Electronics Conference (EQEC)

Field experiments of quantum cryptosystem in 96km installed fibers

Tetsuya Hasegawa, T. Nishioka, Hirokazu Ishizuka, J. Abe, 克宏 清水, M. Matsui

Published Jan 18, 2006• 7 citations
Publisher

Abstract

We have successfully demonstrated quantum cryptosystem in 96 km installed fibers between Osaka and Kyoto, Japan with our dedicated QKD hardware suitable for field experiments. We confirmed that key rate is 8.2 bps and QBER is 9.9%.
DOI
10.1109/eqec.2005.1567470

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We havesuccessfully demonstrated quantum cryptosystem in96kminstalled fibers between OsakaandKyoto, Japan withourdedicated QKD hardware suitable forfield experiments. Weconfirmed that keyrate is8.2bps andQBERis9.9%. Quantum cryptography hastheadvantage ofdetecting eavesdroppers andsecurity guaranteed byafundamental physical law,andisexpected asanabsolutely unbreakable cryptography. Although manylong-distance experiments23 within a laboratory havebeencarried out, aserious QKDfield experiment, except 67kmQKDexperiment' byGeneva Univ., hasnot beenreported yet. Infield experiments compared tothat inlaboratories, there areseveral difficulties tobeovercome, such asfluctuations bytemperature, losses/reflections atconnected points, operations between twodistant points andsoon. Inthis paper, wereport ourfield experiments ofquantum cryptosystem in96kminstalled fibers ofJGNIItestbed between OsakaandKyoto(see Fig. 1). Wehavedesigned compact 1550nmsingle photon detectors andoptics forportable useand electronic control units suitable forfield tests. Andthenwedeveloped atotal portable QKD system applicable toactual fiber networks. Ourdesign policy ofQKD system forfield experiments isthatitscomponents, especially detectors andoptics, are compact forportable use, thesystem canworkstable attwodistant points tofollow timing shifts resulted bytemperature fluctuations andsoforth. We also regarded flexibility asimportant. Therefore wedesigned electronic control units sothat wecould easily change detector's parameters, timing parameters orevenalaser repetition rate (I-IOMHz)whennecessary. Asforsingle photon detectors, wedesigned several parameters toattain about 10-6 darkcount probability andS/Nwhich canlead toabout 100kilometers QKD.Weoperated EPITAXXEPM239BAingated Geiger mode.Wechose anexcess bias voltage as7.1 V(breakdown voltage 44.9V), gate width asInsec(FWHM)andtemperature asabout 203KbyPeltier cooling. Inanother sample, anexcess bias voltage is5.8V(breakdown voltage 44.3V). Asaresult, wehavesuccessfully constructed compact low-noise detectors whosedarkcount probabilities are1.2x10.6, 1.Ox I0-6. Forfield experiments ofquantum cryptosystem, weusedthese compact detectors andourdedicated electronic control units. We adopted modified plugp ) D i __~~~~~~~~~~~~~~~~~~~~~~~~~~~(OIOS Ib A icboPD2 | 7 ~~~~~~~pWbi, cbh-mLAN-TCP/IP Fig.VI.aLAN) Fig. 1.JGNII fiber testbed between OsakaandKyoto Fig 2.Schematic diagram ofexperimental setup
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.