Superconducting Hybrid Rings for Homodyne Detections of Microwave Signals

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1、LUDWIGWALTHER-MEISSNER-BAYERISCHEMAXIMILIANSINSTITUTFURTIEF•-AKADEMIEDERUNIVERSITAT•TEMPERATURFORSCHUNGWISSENSCHAFTENMUNCHEN•SuperconductingHybridRingsforHomodyneDetectionsofMicrowaveSignalsDiplomaThesisElisabethHomannAdvisor:Prof.Dr.RudolfGrossMunich,

2、15February2008LUDWIGMAXIMILIANSUNIVERSITATM•UNCHEN•AbstractDuringthelastyears,thetopicofsuperconductingcircuitquantumelectrodynamicshasattractedincreasinginterest.After,A.Wallraetal.[1]observedthecoherentexchangeofamicrowavesinglephotonbetweenasupercon

3、ductingchargequbitstronglycoupledtoanon-chipmicrowavecavity,itbecameclearthatthecouplingofaquantummechanicaltwo-levelsystemtoamicrowavephotonononechipispossible.In2005M.Mariantoni[2]proposedanexperimentalsetuptodeterministicallygen-eratesinglemicrowavep

4、hotonsinasystemofa uxqubitstronglycoupledtoaresonator.Sincesinglemicrowavephotondetectorsarenotavailableyet,atech-niquesimilartoopticalhomodynedetectionisproposedtodetecttheseextremelyweakmicrowavesignals.Acriticalcomponentinthissetupisa180hybridringwh

5、ichactsasamicrowavebeamsplitter.Thishybridringwillbeconnectedtotheresonatoroutputandtheweakmicrowavesignalwillbesuperimposedwithastronglocaloscillator(LO)signalofthesamefrequency.Theconstructiveanddestructiveinterferencesignalswillgiveinformationaboutth

6、esinglemicrowavephoton.Thisdetectionschemeputsstrongrequirementsonthehybridring.Bothinputportsneedtobeisolatedatthephoton(andLO)frequency,whereasa3dBcouplinghastobeachievedbetweentheinputandtheoutputports.Inthisworkexperimentalresultsofhybridringsofdie

7、rentdesignsandmaterialswillbepresentedandanalyzed.Ashortintroductionofqubitsandthereadoutofweakmicrowavesignalsisgivenintherstchapter.Thetheoreticalbackgroundofamicrowavebeamsplitterisexplainedinchaptertwo,includingtransmissionlinetheory,theoryoftheS-p

8、arametersandthetheoreticalbehaviorofthehybridring.Afterashortdescriptionofthefabricationprocessandtheexperimentalsetupscheme,themeasurementsarepresentedinchaptersfourandve.TheresultsoftheS-parametersareclassiedaccordingtothetwo