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Quantum computing
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R.ColinJohnson4/29/201505:00AMEDT21comments
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News&Analysis
IBMSolvesQuantumComputing
GooglearchitectureobstacletocommercializationPORTLAND,Ore.Quantumcomputersarebeingpursuedbyallthemajorresearchlabsworldwide,includingevennewcomerslikeGoogle.However,IBMclaimsits30yearsofexperienceinquantumcomputingresearchshowsGoogleisallwronginits"linear"design,becauseIBM's"squaretiled"designcansolvebothofthemostimportantproblemsinquantumcomputingpluscanscaletoanysizeneededinthefuture.
IBM'ssearchfortherightarchitectureforquantumcomputersbeganin1981whenitattendedNobelPrizewinnerRichardFeynman'sfirstworkshoponthe"physicsofinformation"wherehelaidouttheconceptofaquantumcomputer.
Overthesubsequent34yearsIBMhasdevelopedFeynman'stheory,inventeditsownarchitectureandconductedexperimentsthattodayhaveledtothedevicesthatcanreliablyscaletoanynumberofqubitsextendingMoore'slawindefinitelysinceitwouldontakeonly50qubitstooutperformthefastestsupercomputerontheTop500.orgsupercomputerlist.
"Wearereportingonafourqubitsystemtoday,andalreadyexperimentingwithaneightqubitsystem,"JerryChow,managerofexperimentalquantumcomputinggroupatIBMResearchCenter(YorktownHeights,N.Y.)toldEETimes."Butunlikeotherdesigns,theseriesofproblemswehavejustsolvedcanscaletoasuperconductingquantumcomputerwithanynumberofqubits."
Thecurrentprototype(seephotos)issupercooledto15milliKelvin,usingacommerciallyavailablesuperrefrigerator,andhassolvedthetwomostimportantproblemsinquantumcomputingtoday,accordingtoIBM,thatissimultaneouslycorrectingforbitflipandphasefliperrorsaswellasbeingcompletelyscalabletoanysize.
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IBM'sfoursuperconductingquantumbitsuseasquarelatticetodetectbothtypesofquantumerrorsbiterrorsandphaseerrorsforthefirsttime.
(Credit:IBMResearch)
"Onthemarchtowardquantumcomputerserrorcorrectionisthemostimportantproblem,becausequbitsarenotasrobustasnormalcomputerbits,"Chowtoldus."Qubitsareveryfragileandcanbespoiledbyallsortsofnoiseintheenvironmentandintherestofthesystem."
Therearetwomaintypesoferrorsthatmustbecorrectedinquantumcomputersbiterrors(flippinga1toa0ora0toa1)andphasefliperrors(whichcausesignalstosubtractfromeachotherinsteadofadd).Unfortunately,itisverydifficulttosolveboththeseerrorsatonce.Todoso,IBMhadtogotoasquarearchitectureinsteadofalineararrayarchitecturelikeGoogle's,whichaccordingtoIBMcanonlysolveoneoftheproblemsortheotherbutnotboth.Asaresult,IBM'ssquarearrayoffourqubitsisquadrupleredundant,butitmakesanerrorfreescalablequantumcomputerpossible.
IBM'ssquarelayoutisthebestconfigurationtoaddmorequbitsandscaletolargersystems.(Credit:IBMResearch)
"Youneednearlyperfectqubitstodomeaningfulcalculationswithaquantumcomputer,soyouhavetodedicatesomequbitstoerrorcorrection,"Chowtoldus."Infact,weareworkingonaneightqubitarchitecturenowtocorrectotherpossibilitiesoferrorinasinglequbitandbelievethatitmaytake13to17qubitsormaybeevenmoretomakeasinglequbitperfectlyreliable."
Thereasonisthatqubitsdonotjustholdasingle0or1likeregularbits,butholdasuperpositionofvalues,"theyarepart0andpart1,whichiswhyitissohardtoperfectlypreservethenduringquantumcalculations,"Chowtoldus.
Inthecurrentfourqubitarchitecture,twoqubitsholdthevaluetobepreserved,whiletheothertwoqubitstellyouwhethertherehavebeenanybitfliporphasefliperrors,respectively.
IBM'sJerryChowinspectingaqubitinthequantumcomputinglabatIBM'sT.J.WatsonResearchCenter.(Credit:JonSimon/FeaturePhotoServiceforIBM)
NextIBMisshootingfortheHolyGrailofquantumcomputingtheperfectincorruptiblequbitthatcouldformthebasisofarealquantumcomputerscalabletoanysize.Toachievethatgoal,IBMplanstoextendthecurrentarchitecturebyaddingmorequbitsinan8bitsurfacecodelatticefornowthatwillofferevenbetterprotectionandcorrectionofquantumerrorsontheroadtotheperfectiontheyneedtostartmarketingrealquantumcomputers.
"Itmaytake8,13,17oreven49qubitsinascalablelatticetorealizetheHolyGrailofperfection,andthearchitecturemayhavetochangetorectangularorhexagonalorsomeothersymmetricalconfiguration,butwenowbelieveitisdefinitelyanachievablegoal."
IBM'squantumcomputingarchitectureusesscalablebuildingblocks,detectsandcorrectsquantumerrors,andwillbeablesolveproblemsconventionalcomputerscannot.
(Source:IBM)
Onceaquantumcomputerisperfecteditwillnotonlybeabletocrackanyencryptioncodetodayandmakenewuncrackablecodes,butwillalsoallowresearcherstounderstandphysicalprocessesthatareimpossibletosimulateoftraditionalcomputersForinstanceallthemolecularinteractionsthatmakecommonprocessesworkallowingdesignerstocreatematerialsimpossibletoimaginetoday,deriveinsightsfromunstructuredBigDatainaninstant,andtrulyunderstandusefulchemicalreactionsthattodaywereonlyfoundbytrialanderror.
"Quantumcomputerswillspawnaneweraofinnovationacrossallindustries,"Chowconcluded.
IBM'sworkwaspartiallyfundedtheU.S.IARPA(IntelligenceAdvancedResearchProjectsActivity)multiqubitcoherentoperationsprogram.
R.ColinJohnson,AdvancedTechnologyEditor,EETimes
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