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1、JournalofModernOpticsVol.55,No.15,10September2008,2359–2370SpontaneousemissionofatomicsystemsinthepresenceofincidentfieldsPeterG.Brooke*CentreforQuantumComputerTechnologyandDepartmentofPhysics,MacquarieUniversity,Sydney,NSW,Australia(Received14March2008;finalversionreceived7Apr
2、il2008)Wecharacterisethespontaneousemissiontimeanddirectionfromsmallnumbersofdipole-coupledtwo-levelatoms(2LAs)inthepresenceofincidentfields.Weshowhowtouseadiabaticpassagetoadmitpopulationtransferbetweenstatesintheone-quantumsubspacefortwoandthree2LAs.Ourmethodisamulti-atomgene
3、ralisationofstimulated-Raman-adiabatic-passage(STIRAP)forasinglemulti-levelatom.Weusenumericalresultstojustifyanansatzthatenablesustogiveanalyticalexpressionsforthedirectionalemissionwhichdependsontheincidentfields.Ourresultsadmitacharacterisationoftheefficacyofpopulationtransf
4、erinsmallnumbersofdipole-coupled2LAs,andareapplicabletoproof-of-principleexperimentsinvolvingdipole-coupled2LAs.Keywords:quantumoptics;STIRAP;dipole–dipole;superradiance1.IntroductionAtomicsystemshaveproventobevaluableforexperimentaldemonstrationsofentanglementandviolationsofBe
5、llinequalities[1],quantuminformationprotocols[2–4],cooperativeeffectssuchassuperradiance[5],andquantumbeats[6].Apairofelectricdipole-coupledtwo-levelatoms(2LAs)hasbeenespeciallywellstudied[7],asthisisthesimplestatomicsystemfordemonstratingtheseeffects,andthree2LAsisthesmallestn
6、umberofatomsthatencodeadecoherence-freequbit(two-levelsystem)[8].Commontoalldemonstrationsofquantumbeats,cooperativeeffects,entanglement,andquantumprocessingtasksistheneedforexternalcontrol.Inmostphysicalsystems,externalcontrolrequiresincidentfields,whichcanalterthecharacterist
7、icsofthesystem.Quantifyingtheeffectofsuchfieldsontheemissionpropertiesofsmallcollectionsof2LAsisonepurposeofthispaper.Wefocusonsystemsinwhichtheatomiccouplingisdescribedbyadipole–dipoleinteraction.Weassumethe2LAsarecloselyseparated,andsopermitonlyglobalcontrol.Previousworkhasqu
8、antifiedglobalpreparation,manipulation,andreadoutofcol
