High-Rate, High-Dimensional Quantum Key Distribution Systems PDF
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Springer Theses Recognizing Outstanding Ph.D. Research Nurul T. Islam High-Rate, High-Dimensional Quantum Key Distribution Systems Springer Theses Recognizing Outstanding Ph.D. Research AimsandScope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected for its scientific excellence and the high impact of its contents for the pertinent fieldofresearch.Forgreateraccessibilitytonon-specialists,thepublishedversions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provideavaluableresourcebothfornewcomerstotheresearchfieldsdescribed,and for other scientists seeking detailed background information on special questions. 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Moreinformationaboutthisseriesathttp://www.springer.com/series/8790 Nurul T. Islam High-Rate, High-Dimensional Quantum Key Distribution Systems Doctoral Thesis accepted by Duke University, Durham, NC, USA 123 NurulT.Islam DepartmentofPhysics DukeUniversity Durham,NC,USA ISSN2190-5053 ISSN2190-5061 (electronic) SpringerTheses ISBN978-3-319-98928-0 ISBN978-3-319-98929-7 (eBook) https://doi.org/10.1007/978-3-319-98929-7 LibraryofCongressControlNumber:2018953017 ©SpringerNatureSwitzerlandAG2018 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Thepublisher,theauthors,andtheeditorsaresafetoassumethattheadviceandinformationinthisbook arebelievedtobetrueandaccurateatthedateofpublication.Neitherthepublishernortheauthorsor theeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinorforany errorsoromissionsthatmayhavebeenmade.Thepublisherremainsneutralwithregardtojurisdictional claimsinpublishedmapsandinstitutionalaffiliations. ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG. Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Thisdissertationisdedicatedtomyparents. Supervisor’s Foreword Dr. Nurul T. Islam’s thesis describes a broad research program on the topic of quantum communication. Here, a cryptographic key is exchanged by two parties usingquantumstatesoflightandthesecurityofthesystemarisesfromthefunda- mental properties of quantum mechanics. Dr. Islam develops new communication protocols using high-dimensional quantum states so that more than one classical bit is transferred by each photon. This approach helps circumvent some of the non-ideal properties of the experimental system, allowing him to achieve record key rates on metropolitan distance scales. Another important aspect of the work is the encoding of the key on high-dimensional phase-randomized weak coherent states, combined with the so-called decoy states to thwart a class of possible attacks on the system. The experiments are backed up by a rigorous security analysis of the system, which accounts for all known device non-idealities. Dr. Islam goes on to demonstrate a scalable approach for increasing the dimension of the quantum states and considers attacks on the system that use optimal quantum cloning techniques. The thesis captures the current state of the art of the field of quantum communication in laboratory systems and demonstrates that phase- randomizedweakcoherentstateshaveapplicationbeyondquantumcommunication. In greater detail, the introductory Chap.1 introduces the basics of cryptography andpointstotheneedforpost-quantumcryptographicmethodsthatwillbesecure in the presence of an attacker with a large-scale quantum computer. Quantum key distribution offers one potential solution, but additional research is needed to improve the secure key rate of these systems and to analyze their security in the presence of experimental imperfections. The chapter then introduces the dissertation, highlighting the original contributions to the field. Chapter 2 is a pedagogicalintroductiontoquantumkeydistributionusingtwo-dimensional(qubit) time-phasestates.Here,aquantumphotonicwavepacketisinoneoftwocontingent timeslotsinthecommunicationsystem(temporalbasis)orinbothtimeslotswitha relativephasedifference(phasestates).Thereaderiswalkedthroughaquantumkey distributionsessionusingthesestatesandsomepossibleattacksbyaneavesdropper are discussed. The chapter is rounded out by discussing a possible experimental realizationofaquantumkeydistributionsystem,highlightinghowthephasestates vii viii Supervisor’sForeword can be measured at the receiver using thermally insensitive delay interferometers (describedingreaterdetailinAppendicesAandB).Athoroughdiscussionofafour- dimensional time-phase quantum key distribution system is presented in Chap.3. Here,Dr.Islamusedphase-randomizedweakcoherentstatesatthetransmitterand identifies the fraction of the transmitted states for which the photonic wavepacket hasoneorlessphotonsusingthedecoy-stateprotocol.Acurrentrecord-highsecure rateisobtainedwiththissystemforchannellossesusefulforametropolitan-scale quantum key distribution network. Dr. Islam achieved this result by paying strict attention to experimental non-ideal behaviors, especially single-photon detector saturation. The experimental work is complemented with a full security analysis using entropic uncertainty relations, a state-of-the-art theoretical approach for this problem with additional details given in Appendix C. Following in Chap.4 is a security analysis for a quantum key distribution system does not use all quantum states. A quantum key distribution system is secured using at least two mutually unbiased bases. For a d-dimension system, there are d states in each basis and each state on both bases needs to be chosen randomly and sent by transmitter. An analysis is presented here to show that only d states in one basis and one state in the other basis need to be used without substantial loss in key rate provided that the quantum bit error rate is low. This result is important for practical application for high-dimensional quantum key distribution systems and can be applied to any quantum photonic states. Going beyond a four-dimensional Hilbert space used in Chap.3, Dr. Islam presents in Chap.5 a new method for measuring phase states using a weak local oscillator and two-photon interference at the receiver. This approach does not require delay interferometers and hence is readily scaled to higher dimensions. Using this system along with the efficient security approach described in Chap.4, Dr. Islam observes that detector saturation reduces the key rate at low channel loss; increasing the dimension helps avoid saturation effects, but eventually lowers the rate for large dimension. Thus, the secure key rate is optimizedforadimensionthatisalwayslargerthantwoforthissystem.Chapter6 describesonetypeofattackonahigh-dimensionalquantumkeydistributionsystem enabled by optimal quantum cloning. Previous experiments on optimal quantum cloninguseheraldedsingle-photonstatesgeneratedbyparametricdownconversion. Here, Dr. Islam demonstrates that optimal quantum cloning is also possible using phase-randomizedweakcoherentstateswiththedecoy-stateprotocol,whichiswell matchedtothetransmitterusedinthequantumkeydistributionsystem.Consistent with previous work, the fidelity of the cloned state decreases with dimension and hencethesecurityofthesystemincreasesassumingconstantbiterrorrate.Finally, Dr. Islam summarizes his original contributions and points to future directions in thefinalconclusionchapter. Columbus,OH DanielJ.Gauthier Acknowledgments Iwouldliketoacknowledgetheguidanceandsupportofmyadviser,Prof.Daniel Gauthier. Over the last 4 years, I have greatly appreciated and benefited from the amount of time he dedicates to his students, the way he motivates and encourages everyonetocollectbetterdata,andtherateatwhichherespondstoemailqueries. Itisanabsoluteprivilegetolearnunderhisguidance.IwouldliketothankDanfor puttingupwithmeoverthelast4years,andhiswillingnesstocontinuetodoso. IwouldalsoliketoacknowledgethesupportofProf.JungsangKim,whoafter Dan moved to OSU, provided me with a lab space, equipment, and an incredible environment to work. I would also like to thank him for realizing that the high- efficiencysingle-photondetectorswerecriticalfortheseprojects.Onthesamenote, I would also like to thank Clinton Cahall for his work on the cryogenic readout circuitsthatIhaveusedtocollectmostofthedatapresentedhere.Finally,Iwould liketothankDr.CharlesCiWenLimforteachingmethebasicsofsecurityproofs and for patiently explaining to me why I should always check my intuition with calculation. I am grateful to my preliminary and thesis committee members, Prof. Harold Baranger,Prof.KateScholberg,andProf.HenryEveritt,forthehelpfuldiscussion andquestionsandfortakingthetimetoreadthroughthiswork. I would like to acknowledge all the past members of the Qelectron research group who overlapped a portion of their graduate school or postdoctoral life with me—Michael, Bonnie, Hannah, Andres, Otti, Lou, David, Nick—and the only other present member Meg, for all the conversations, laughter, physics-related discussions,etc. Duringgraduateschool,itisveryeasytoloseperspectiveonthebiggerpicture oflife.IwouldliketothankAryaRoyforconstantlyremindingmeofthat,andall the free coffee and great conversations about history, politics, sports, and physics. Forthesamereasons,averyspecialthankstomyfriendsofgrads13—Gleb,Yingru, Agheal, Ming—who kept me going with frequent lunch meetings and hangouts. I wouldliketothankPayalforthecompanyduringlongworkdaysandeveningsand forproofreadingmostofthisthesis. ix x Acknowledgments I also want to thank my college Professors, Dr. Harmon and Dr. Haring-Kaye, for constantly checking-in with me during my time at Duke. I want to thank Mrs. Harmon for all the free food and care. Finally, I would like to thank my parents andsisterfortheirconstantsupport,understanding,andpatience.Theyhavealways managedtokeepmeshieldedfromtheday-to-dayactivitiesathome. I would like to gratefully acknowledge the support of the Office of Naval Research MURI program on Wavelength-Agile Quantum Key Distribution in a Marine Environment, Grant # N00014-13-1-0627, for funding my research work atDuke.
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