Chapter 9_ Quantum emitters_ atoms， molecules， quantum dots， .. .pdf

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1、Chapter9Quantumemitters9.1IntroductionandBasicsTheinteractionoflightwithnanometer-sizedstructuresisatthecoreofnano-optics.Itisobviousthatastheparticlesbecomesmallerandsmallerthelawsofquantummechanicswillbecomeapparentintheirinteractionwithlight.Inthislimit,contin-uo

2、usscatteringandabsorptionoflightwillbesupplementedorreplacedbyresonantinteractionsifthephotonenergyhitstheenergydifferenceofdiscreteinternal(elec-tronic)energylevels.Inatoms,molecules,andnanoparticles,likesemiconductornanocrystalsandother’quantumconfined’systems,these

3、resonancesarefoundatopticalfrequencies.Duetotheresonantcharacter,thelight-matterinteractioncanoftenbeapproximatedbytreatingthequantumsystemasaneffectivetwo-levelsys-tem,i.e.byconsideringonlythosetwo(electronic)levelswhosedifferenceinenergyisclosetotheinteractingphoton

4、energy¯hω0.Inthischapterwewillconsidersinglequantumsystemsthatarefixedinspace,eitherbydepositiontoasurfaceorbybeingembeddedintoasolidmatrix.Thematerialtobecoveredshouldfamiliarizethereaderwithsingle-photonemittersanddetectorsandwithconceptsdevelopedinthefieldofquantum

5、optics.Whilevari-oustheoreticalaspectsrelatedtothefieldsemittedbyaquantumsystemhavebeendiscussedinChapter??,thecurrentchapterfocusesmoreonthenatureofthequan-tumsystemitself.Wewilladoptaratherpracticalperspectivesincemorerigorousaccountscanbefoundelsewhere(seee.g.[1-4

6、]).12CHAPTER9.QUANTUMEMITTERS9.2FluorescentmoleculesForanorganicmolecule,thelowestenergyelectronictransitionappearsbetweenthehighestoccupiedmolecularorbital(HOMO)andthelowestunoccupiedmolecularorbital(LUMO).Higherunoccupiedmolecularorbitalscanbetakenintoaccountifnec

7、essary.Inadditiontotheelectronicenergylevels,largerparticles,suchasmolecules,havevibrationaldegreesoffreedom.Formolecules,allofthementionedelectronicstatesinvolvedintheinteractionofamoleculewithlighthaveamani-foldof(harmonic-oscillator-like)vibrationalstatessuperimp

8、osed.Sincethenucleihavemuchmoremassthantheelectrons,thelatterareconsideredtofollowthe(vibrational)motionofthenucleiinstantaneously.Withint