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Quantum computing



Basicprinciple

Theprincipleofsuperpositionofquantummechanicalstatesmakesthestateofquantuminformationunitinasuperpositionstateofmultiplepossibilities,resultinginquantuminformationprocessingintermsofefficiencycomparedtoclassicalinformationprocessingHasgreaterpotential.The2-bitregisterinanordinarycomputercanonlystoreoneofthefourbinarynumbers(00,01,10,11)atatime,whilethe2-bitqubitregisterinaquantumcomputercanstorethesefouratthesametimeThestateofsuperposition.Asthenumberofqubitsincreases,fornqubits,quantuminformationcanbeinasuperpositionoftwopossiblestates.Withtheparallelismofquantummechanicsevolution,itcanshowfasterprocessingspeedthantraditionalcomputers.

Qubit

Qubitisthetheoreticalcornerstoneofquantumcomputing.Inaconventionalcomputer,theinformationunitisrepresentedbyabinarybit.Itiseitherinthe"0"stateorinthe"1"state.Inabinaryquantumcomputer,theinformationunitiscalledaqubit,exceptforthe"0"state.Inadditiontothe"1"state,itcanalsobeinasuperposedstate.

Thesuperpositionstateisanylinearsuperpositionofthe"0"stateandthe"1"state.Itcanbeeitherthe"0"stateorthe"1"state.The"0"stateandthe"1"stateareeachExistatthesametimewithacertainprobability.Bymeasuringorinteractingwithotherobjects,itpresentsa"0"stateora"1"state.Anytwo-statequantumsystemcanbeusedtorealizequbits,suchasthegroundstateofelectronsinhydrogenatoms(Groundstate)andthefirstexcitedstate(firstexcitedstate),the+1/2componentand-1/2componentoftheprotonspininanydirection,theleftandrightrotationofcircularlypolarizedlight,etc.

Aquantumsystemcontainsanumberofparticles,whichmoveaccordingtothelawsofquantummechanics,andthesystemissaidtobeinacertainquantumstateinthestatespace.Thestatespacementionedherereferstothevectorspaceformedbymultipleeigenstates(basicquantumstates).Thebasicquantumstateisreferredtoasbasicstateorbasicvector.StateSpacecanbeexpressedbyHilbertspace(linearcomplexvectorspace),thatis,Hilbertspacecanexpressvariouspossiblequantumstatesofaquantumsystem.Inordertofacilitaterepresentationandoperation,Diracproposestousethesymbol|x>torepresentthequantumstate,and|x>isAcolumnvectoriscalledket;itsconjugatetranspose(conjugatetranspose)isrepresentedby〈x|,〈x|isarowvector,calledbra.Thesuperpositionstateofaqubitcanbeusedintwo-dimensionalHilbertspace(ieTwo-dimensionalcomplexvectorspace)unitvectortodescribe.

Superpositionprinciple

Thinkofquantumasanelectroninamagneticfield.Theelectron'srotationmaycoincidewiththemagneticfield,whichiscalledtheup-spinstate,ortheoppositeofthemagneticfield,whichiscalledthedown-spinstate.Ifwecanuseanenergypulsetoflipthelowerspinstateintoanupperspinstateunderthepremiseofeliminatingexternalinfluences;then,ifweusehalfoftheenergypulse,thelowerspinstatewillbepreparedintoalowerspinstate.Inthestatewherethespinandtheupperspinaresuperimposed(theprobabilityofbeingineachstateisone-half).Fornqubits,itcancarryasuperpositionof2statestothepowerofn.Theoperatingprocessofquantumcomputersiscalledunitaryevolution,andunitaryevolutionwillensurethateverypossiblestateevolvesinaparallelmanner.Thismeansthatifaquantumcomputerhas500qubits,eachstepofquantumcomputingwilloperateon2500possibilitiesatthesametime.2500isaterriblenumber,itismorethanthenumberofatomsknownontheearth(thisistrueparallelprocessing,today’sclassiccomputers,theso-calledparallelprocessorisstillonlyonetimeonething).

Actionplan

In2016,theEuropeanUnionannouncedthelaunchofaUS$1.1billion"QuantumFlagship"program;Germanyannounceda650millioneurosNationalQuantumPlaninAugust2019;ChinaandtheUnitedStatesChinahasalsoinvestedbillionsofdollarsinquantumscienceandtechnology.Thiscompetitionaimstobuildaquantumcomputerthatperformsbetterthantraditionalcomputersoncertaintasks.InOctober2019,Googleannouncedthataquantumprocessorthatperformsspecificcomputingtaskshasachievedthisquantumhegemony.

OnDecember6,2019,RussianDeputyPrimeMinisterMaximAkimovproposedtheNationalQuantumActionPlanattheTechnologyForumheldinSochi.ItplanstoinvestapproximatelyUS$790millionin5yearstobuildaTaiwanisapracticalquantumcomputerandhopestocatchupwithothercountriesinthefieldofpracticalquantumtechnology.

Development

ConceptProposal

TheconceptofquantumcomputationwasfirstproposedbyP.BenioffoftheArgonNationalLaboratoryintheearly1980s.HeItisproposedthatasecond-levelquantumsystemcanbeusedtosimulatedigitalcalculations;Feynmanalsobecameinterestedinthisproblemandbegantostudy,andgaveasessionintheFirstConferenceonPhysicsofComputationheldattheMassachusettsInstituteofTechnologyin1981.Thespeechoutlinesthevisionofrealizingcomputingwithquantumphenomena.In1985,D.DeutschofOxfordUniversityputforwardtheconceptofquantumTuringmachine,andquantumcomputingbegantohavethebasicformofmathematics.However,mostoftheabove-mentionedquantumcomputingresearchislimitedtoexploringthephysicalnatureofcomputing,andisstillatafairlyabstractlevel,andhasnotyetenteredthestageofdevelopingalgorithms.

Mid-termdevelopment

In1994,P.Shor,anappliedmathematicianatBellLabspointedout[3]thatcomparedtotraditionalelectroniccalculators,quantumcomputingcanbeusedinashortertimeInsidedecomposesalargeintegerintotheproductofprimefactors.Thisconclusionopensanewstageofquantumcomputing:Quantumalgorithms,whicharedifferentfromtraditionalcalculationrules,dohavepracticalityandarebynomeansatrickinthepocketsofscientists.Sincethen,newquantumalgorithmshavebeenproposedoneafteranother,andoneoftheimportantissuesfacingphysicistsnextishowtobuildarealquantumcalculatortoexecutethesequantumalgorithms.Manyquantumsystemshavebeennamedastheinfrastructureofquantumcalculators,suchasphotonpolarization(photonpolarization),cavityquantumelectrodynamics(CQED),iontrap(iontrap),andnuclearmagneticresonance(nuclearmagneticresonance).,NMR)andsoon.Asof2017,consideringfactorssuchassystemscalabilityandcontrolaccuracy,iontrapsandsuperconductingsystemsareaheadofotherphysicalsystems.

InAugust2019,China'squantumcomputingresearchmadeimportantprogress:scientistsledtherealizationofhigh-performancesingle-photonsources.PanJianwei,anacademicianoftheChineseAcademyofSciencesandaprofessorattheUniversityofScienceandTechnologyofChina,ledbyLuChaoyang,HuoYonghengandothers,andcooperatedwithmanydomestic,German,andDanishscholarstoproposeanewtheoreticalsolutionforthefirsttimeintheworld,whichisbasedonthenarrowbandandbroadbandmicrocavities.Thesuccessfulrealizationofasingle-photonsourcewithdeterministicpolarization,highpurity,highidentityandhighefficiencyhaslaidanimportantscientificfoundationforopticalquantumcomputerstosurpassclassicalcomputers.Theinternationalauthoritativeacademicjournal"NaturePhotonics"recentlypublishedtheresults,commentingthatit"solvesalong-standingchallenge."

Developmentprospects

Quantumcomputingwillmakeitpossibleforcomputerstogreatlyexceedthecomputingpoweroftoday’scomputers,buttherearestillmanyobstacles.Animportantprobleminlarge-scalequantumcomputingishowtomaintainthequantumcoherenceofenoughqubitsforalongtime,whileatthesametimebeingabletomakeenoughquantumlogicoperationswithultra-highprecisionwithinthistimeperiod.

Theworld’sfirstcommercialquantumcomputer

CanadianquantumcomputingcompanyD-Waveofficiallyreleasedtheworld’sfirstoneonMay11,2011Commercialquantumcomputer"D-WaveOne",thedreamofquantumcomputerisabigstepclosertous.D-Wave'ssloganis-"Yes,youcanhaveone."Infact,asearlyasthebeginningof2007,D-WaveCompanydemonstratedtheworld’sfirstcommercialandpracticalquantumcomputer"Orion"(Orion),butstrictlyspeaking,thesystemwasnotreallyaquantumcomputeratthetime,butitcouldbeused.Somespecial-purposemachineswithquantummechanicsmethodstosolveproblems.

General-purposetasksarefarfromtheopponentsoftraditionalsiliconprocessors,andprogrammingneedstobere-learned.Inaddition,inordertoreducetheenergylevelofqubitasmuchaspossible,itisnecessarytouseniobiuminthelow-temperaturesuperconductingstatetoproducequbit,andtheoperatingtemperatureofD-Waveneedstobekeptnearabsolutezero(20mK).

Quantumcomputingwillmakeitpossibleforcomputerstogreatlyexceedthecomputingpoweroftoday’scomputers,buttherearestillmanyobstacles.Oneproblemwithlarge-scalequantumcomputingisthatitisdifficulttoimprovetheaccuracyoftherequiredquantumdevices.

InJanuary2017,D-WavelaunchedD-Wave2000Q.Theyclaimedthatthesystemconsistsof2000qubitsandcanbeusedtosolveproblemssuchasoptimization,networksecurity,machinelearning,andsampling.Forsomebenchmarkproblems,suchasoptimizationproblemsandmachinelearning-basedsamplingproblems,D-Wave2000Qoutperformsthecurrenthighlyspecializedalgorithms1000to10,000times.

D-WaveOnequantumcomputersystemandD-WavecompanyfounderandCTOGeordieRose

Thefirstnon-localquantumsimulatordevelopedbytheUniversityofScienceandTechnologyofChina

TheresearchgroupofProfessorLiChuanfengfromtheKeyLaboratoryofQuantumInformationoftheUniversityofScienceandTechnologyofChinadevelopedanon-localquantumsimulatorforthefirsttime,andsimulatedthesuperluminalphenomenonintheworldofParity-time(PT).

Thisexperimentfullydemonstratestheimportantroleofnon-localquantumsimulatorsinthestudyofquantumphysicsproblems.

Quantumsimulatorsarededicatedquantumcomputersthatsolvespecificproblems.ThisconceptwasfirstproposedbyFeynmanin1981.Feynmanbelievesthatnatureessentiallyfollowsquantummechanics,andonlyadevicethatfollowsquantummechanicscansimulateitbetter.Thismechanicaldeviceisaquantumsimulator.Inthestudyofquantumsimulators,peoplepaymoreattentiontoitsquantumaccelerationcapabilities.Generally,themorequbitscontrolledbyaquantumsimulator,thestrongeritscomputingpower.

Huawei’sfirstexposuretoquantumcomputingresults

OnOctober12,2018,Huaweiannouncedthelatestprogressinthefieldofquantumcomputing:quantumcomputingsimulatorHiQThecloudserviceplatformcameout.TheplatformincludestheHiQquantumcomputingsimulatorandtheHiQquantumprogrammingframeworkdevelopedbasedonthesimulator.Thisisthecompany'sfirststepinthefundamentalresearchofquantumcomputing.

BaidulaunchesBaiduQuantumPlatform

OnSeptember15,2020,the"BaiduWorld2020"conferencewillbeheldonline,BaiduResearchInstituteQuantumComputingInstituteThedirectorDuanRunyaoreleasedtheBaiduQuantumPlatform,demonstratingtheBaiduQuanmai+QuantumPaddle+Quanyifuempoweringnewinfrastructureandpursuingthevisionof"everyonecanbequantum".Heintroduced,“Baiduhasnewlyreleasedthefirstcloud-nativequantumcomputingplatforminChina,QuanYiFu,andcomprehensivelyupgradedthequantumpulsecloudcomputingservicesystem,QuantumPulseandQuantumMachineLearningDevelopmentTool,QuantumPaddle.Ecologyopensthedoortothequantumera."BaiduQuantumPlatformprovidesalargenumberofsoftwaretoolsandinterfacesrequiredtoconnecttop-levelsolutionsandunderlyinghardwarefoundations.Baiduhopesthatthisplatformwillplaytheroleofanoperatingsysteminthequantumcomputingera,developersandpartnersTheempowermentofquantumcomputingtotheindustrycanberealizedthroughthisplatform.

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