SinglePhotonEmittersandtheiruseinQuantumCryptography单光子发射和它们的使用在量子密码

SinglePhotonEmittersandtheiruseinQuantumCryptographyPresentationby:BramSlachterSupervision:Dr.Ir.CasparvanderWalContentsTheIdealsinglephotonemitterExampleoftheiruse:QuantumCryptographyinanutshellExperimentalsetupsOverviewofvarioussinglephotonemitters:QuantumdotsinglephotonemittersQuantum‘well’singlephotonemitters*Moleculesinglephotonemitters*ColourCentresinglephotonemitters*ConclusionTheidealsinglephotonemitterSinglephotonpulsesondemandPulseshaveidenticalwavepacketsRoomtemperatureoperationEasytocreateFrequencytuneableTheidealsinglephotonemitter:StatesoflightMaxwelleqsforacubegiveEMmodeswithdiscreteandpolarizationEMmodesbehaveasH.O.WhenquantizedthesegivetraditionalQMH.O.levelswithenergy.

FortheseEMmodes:welldefinedandundefinedduetonumberphaseHeisenbergminimumuncertaintyClassicallight(laserlight,thermallight)insuperpositionofthesestates:(Super)PoissonianTheidealsinglephotonemitter:StatesoflightInreality:‘infinite’cube->quantizationbecomescontinuous->discretegoestocontinuous.Continuousmodeexcitationnowlocalizedinwavepacketswithdistributionin:

WavepacketexcitationstilldefinedbynumberandphasebutalsohasadistributionTheidealsinglephotonemitterSinglephotonwavepackets:lowestexcitationpossibleConsecutivewavepacketsemitted->samewavepacketsQuantumCryptographyinaNutshellModerncryptography:encryptionanddecryptionproceduresdependonasecretkeyThiskeyconsistsofarandomlychosenstringofbitswhichneedstobesharedonceinawhile:keydistributionproblemMathematicalsolution:publickey–privatekeyinsecurewhenquantumcomputerbecomesavailableQuantumkeydistributionEntangledstatesNonorthogonalstates*QuantumCryptographyinaNutshellSendersendsarandomkeywitheachbitencodedinarandombasisDetectionbasisrandomforeachbitOverapublicchannelthebaseschosenforeachbitarecomparedandtheoneswiththerightbasesarekeptRandomlychosenpartoftheremainingkeyispubliclycheckedforerrorsNoerrors->safekeyestablishedExperimentalSetups:

HanburyBrownTwistexperimentDeterminationmultiplephotonsuppression: HBTexperimentCalculation:TwophotonsuppressionSantorietal,Nature419pg595(2002)Classical:ExperimentalSetups:twophotoninterferenceIndistinguishabilityconsecutivephotonsinexperiments->wavepacketoverlapTwophotoninterference:Whentwophotonsentera50-50beamsplitterfromeachsidetheycanonlyleavetogether:knownasthe‘bunching’ofphotonsnonentangledinput:ExperimentalSetups:twophotoninterferenceSantorietal,Nature419pg595(2002)OverviewSinglePhotonEmitters:

QuantumDotSPESemiconductorquantumdotDiscretelevelsChargingeffectsCreatedbyMBE,EtchingandE-beamExcitedwithalaser:Santori

etal,Nature419pg595(2002)Michler

etal,Science290pg2282(2000)1)2)OverviewSinglePhotonEmitters:

QuantumDotSPESemiconductorquantumdotDiscretelevelsChargingeffectsExcitedwithalaser.ChargingeffectsusedforsinglephotonselectionMichleretal,Science290pg2282(2000)OverviewSinglePhotonEmitters:

QuantumDotSPE

Wavepacketoverlapbytwophotoninterference0.7-0.8.Problem:RoomtemperatureoperationhardduetoopticalphononemissioninthebulkPerformancereasonable:lifetimelimitedBigadvantage:electricalexcitationpossiblewithp-i-njunctionwithquantumdotsinintrinsicregion.Yuanetal,Science295,pg102(2002)OverviewSinglePhotonEmitters:

QuantumWellSPEPoststructurescreatedwithMBE,E-BeamLithographyandplasmaetchingUsessimultaneousCoulombblockadeforelectronsandholesIntrinsicquantumwellseparatedbytunnelbarriersfromann-andp-dopedquantumwelllyinginahostmaterialOperatingat20mKKimetal,Nature397,pg500(1999)OverviewSinglePhotonEmitters:

QuantumWellSPEOverviewSinglePhotonEmitters:

QuantumWellSPEFrequencycontrolledcurrentConductancequantizationKimetal,Nature397,pg500(1999)OverviewSinglePhotonEmitters:

QuantumWellSPENoHBTexperimentbutthoseareprobablyprettygood.Roomtemperatureoperationhard:Smallerquantumdotsneeded->biggerenergyspacingandcoulombeffectsHigherpotentialbarrierstosuppressnonradiativedecayOverviewSinglePhotonEmitters:

MoleculeSPELasertargetedatasinglemolecule:LaserlightfilteredHighlyFluorescentandtemperaturestablemoleculesneededOverviewSinglePhotonEmitters:

MoleculeSPEMoleculeshavebeenreportedwhichworkatroomtemperature.Lounis&Moerner,Nature407,pg491(2000)ReasonabletwophotonsuppressionbutnotalwayseasytoprocessOverviewSinglePhotonEmitters:

MoleculeSPEAlsoasetuppossiblebasedonadiabaticfollowing:Bruneletal,Phys.Rev.Lett.83,pg2722(1999)OverviewSinglePhotonEmitters:

ColourCentreSPESame4levelprincipleasbeforeDiamondnanocrystalsgrownfromdiamondpowder.NitrogenimpuritiesnaturallypresentByelectronbombardmentvacanciesproducedwhichmovenexttonitrogenimpuritiesbyannealingNitrogen-VacancycolourcentreproducedReasonabletwophotonsuppressionandroomtemperaturestableCanbespincoatedbutthedifficultlyoftargetingthenanocrystalsremainsConclusionAllstructuresinprinciplecapableofproducingroom