带状双层石墨上的自旋量子比特

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1、▲，-^IAbstractRecently,onthehorizonofmaterialsscienceandcondensed—matterphysics，arapidlyrisingstarappears，whichistheso-calledgraphene．Thisperfectlytwo-dimensionalmaterialshowsoutstandinglyhighelectronicandcrystalqual-ity．Withoutbeingaffectedbyitsshorthistory,graphenehasopenedana

2、bundantsourceofnewphysicsandpotentialapplications．Scientistshavejustuncoveredtheverytipoftheicebergofitsqualitiesandapplications，althoughitsexperi-mentsandtheoriesareexceptionallyrapidlyprogressing．Inthethesis，wemainlyfocusontherealizationofspinqubitsviaquantumdotsinthegraphene

3、ribbonandbilayergrapheneribbon．Intheintroductionchapter，webrieflyreviewtheexperimentalandtheoreticalbreakthroughsongrapheneinrecentyears．InChapterTwo，we’introducetheDiracFermionasthelowenergyexcitatiohsofthegraphene，basedonthefieldtheory．Wethendiscusstwo-dimensionalhoneycomblat

4、ticeinthenearest—neighbortight—bindingmodel．Wederivetheeffective-massequationwithinthecalledk·Papproximation．InChapterThree，weconsiderelectronicstatesofgrapheneribbonwitharm-chairandzigzagedges，respectively．Forthearmchairedge，bandstructureisinsulatingwhenthewidthoftheribboninla

5、tticeconstantunitshastheforms3Mor3M+2，withMallinteger，andmetallicotherwise．InChapterFour，wediscusshowtorealizespinqubitsingrapheneviaquantumdots．Here，twodifficultiesmayarise：(1)Asthereisnoenergygapingraphenespectrum，SOitishardtoformtunablequantumdotsingraphene．(2)Sincethevalley

6、degeneracyexistsingraphene，thereisnoHeisenbergexchangecouplingbetweentwoneighboringquantumdots．However，wemaysolvethesetwoprob-lemsatoncebyusingtunabletransversestatesingrapheneribbonwitharmchairedges．AsdiscussedinChapterThree，anenergygapwithtensofmeVappears哞2onthiskindofgraphen

7、eribbon，SOthevalleydegeneracyisliftedandtheHeisen-bergexchangecouplingappears．Moreover，itisshownthatthespinqubitsinquantumdotsimplementedinthearmchairgrapheneribboncanbecorrelatedbyeachotheroverawidedistance．InChapterFive，wesuggestthatthespinqubitscanbealsorealizedinthebilayerg

8、rapheneribbonwitharmchairedges．Wefindthattheinterlayer