Observation of the Dynamical Casimir Effect in a Superconducting Circuit

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1、ObservationoftheDynamicalCasimirEectinaSuperconductingCircuitC.M.Wilson1,G.Johansson1,A.Pourkabirian1,J.R.Johansson2,T.Duty3,F.Nori2;4&P.Delsing11Depart.ofMicrotechnologyandNanoscience,ChalmersUniversityofTechnology,G•oteborg,Sweden2AdvancedScienceInstitu

2、te,RIKEN,Wako-shi,Saitama351-0198,Japan3UniversityofNewSouthWales,Sydney,NSW,2052Australiaand4UniversityofMichigan,AnnArbor,MI48109,USA(Dated:May25,2011)PACSnumbers:arXiv:1105.4714v1[quant-ph]24May20111Oneofthemostsurprisingpredictionsofmodernquantumtheory

3、isthatthevacuumofspaceisnotempty.Infact,quantumtheorypredictsthatitteemswithvirtualparticles ittinginandoutofexistence.Whileinitiallyacuriosity,itwasquicklyrealizedthatthesevacuum uctuationshadmeasurableconsequences,forinstanceproducingtheLambshift[1]ofato

4、micspectraandmodifyingthemagneticmomentfortheelectron[2].Thistypeofrenormalizationduetovacuum uctuationsisnowcentraltoourunderstandingofnature.However,theseeectsprovideindirectevidencefortheexistenceofvacuum uctuations.Fromearlyon,itwasdiscussedifitmighti

5、nsteadbepossibletomoredirectlyobservethevirtualparticlesthatcomposethequantumvacuum.40yearsago,Moore[3]suggestedthatamirrorundergoingrelativisticmotioncouldconvertvirtualphotonsintodirectlyobservablerealphotons.ThiseectwaslaternamedthedynamicalCasimireec

6、t(DCE).Usingasuperconductingcircuit,wehaveobservedtheDCEforthersttime.Thecircuitconsistsofacoplanartransmissionlinewithanelectricallengththatcanbechangedatafewpercentofthespeedoflight.Thelengthischangedbymodulatingtheinductanceofasuperconductingquantumint

7、erferencedevice(SQUID)athighfrequencies(11GHz).Inadditiontoobservingthecreationofrealphotons,weobservetwo-modesqueezingoftheemittedradiation,whichisasignatureofthequantumcharacterofthegenerationprocess.Thatamirrorcanbeusedtomeasurevacuum uctuationswasrst

8、predictedbyCasimirin1948[4].Casimirpredictedthattwomirrors,i.e.perfectlyconductingmetalplates,heldparalleltoeachotherinvacuumwillexperienceanattractiveforce.Essentially,themirrorsreducethedensityofelectromagn