REPORTS

initiallyalignedwiththisdirectionemittedpurecircularlypolarizedphotonsandremainedin-variantunderscattering.Theirsuperpositions,ontheotherhand,becameentangledwiththescat-teredphotonpolarization.Statesthatareinvariantundercouplingtotheenvironmentareofinterest,notonlybecauseoftheirimportanceinthequan-tummeasurementprocessbutalsobecauseoftheirpotentialuseforquantumcontrolpurposes.Invariantstatescanspandecoherence-freesub-spacesinwhichquantuminformationcanbeprotected(21).Itwouldbethereforeinterestingtosearchformulti-spinstatesthatareinvariantunderphotonscattering,anddetection,byusinglargerarraysoftrappedions.

ReferencesandNotes

1.W.H.Zurek,Rev.Mod.Phys.75,715(2003).2.Thismechanismisdifferentthantheprocessof

ein-selectionindecoherencetheory,inwhichthemutualinteractionbetweenaquantumsystem,ameasurement

3.4.5.6.7.8.9.10.11.12.13.14.15.16.

apparatus,andtheirenvironmentresultsintheemergenceofapreferredbasis(1).

C.J.Myattetal.,Nature403,269(2000).

M.Bruneetal.,Phys.Rev.Lett.77,4887(1996).

M.S.Chapmanetal.,Phys.Rev.Lett.75,3783(1995).M.Mei,M.Weitz,Phys.Rev.Lett.86,559(2001).D.A.Kokorowski,A.D.Cronin,T.D.Roberts,D.E.Pritchard,Phys.Rev.Lett.86,2191(2001).R.Ozerietal.,Phys.Rev.Lett.95,030403(2005).H.Uysetal.,Phys.Rev.Lett.105,200401(2010).N.Akerman,S.Kotler,Y.Glickman,R.Ozeri,Phys.Rev.Lett.109,103601(2012).

D.B.Hume,T.Rosenband,D.J.Wineland,Phys.Rev.Lett.99,120502(2007).

A.H.Myersonetal.,Phys.Rev.Lett.100,200502(2008).A.Keselman,Y.Glickman,N.Akerman,S.Kotler,R.Ozeri,NewJ.Phys.13,073027(2011).

B.B.Blinov,D.L.Moehring,L.M.Duan,C.Monroe,Nature428,153(2004).

J.Volzetal.,Phys.Rev.Lett.96,030404(2006).N.Akerman,S.Kotler,Y.Glickman,A.Keselman,R.Ozeri,App.Phys.B,10.1007/s00340-011-4807-6(2011).

MaterialsandmethodsareavailableassupplementarymaterialsonScienceOnline.

18.Cohen-Tannoudji,ClaudeandDiu,BernardandLaloe,

Frank,QuantumMechanics(Wiley-Interscience2006),Vol.2,p.1048.

19.M.A.Nielsen,I.L.Chuang,QuantumComputationand

QuantumInformation(CambridgeUniv.Press,Cambridge,2000).

20.M.B.Plenio,S.Virmani,put.7,

1(2007).

21.D.A.Lidar,I.L.Chuang,K.B.Whaly,Phys.Rev.Lett.81,

2594(1998).Acknowledgments:Y.G.andS.K.haveequallycontributedtothiswork.WethankN.DavidssonandD.Stamper-Kurnforusefulcommentsonthemanuscript.Wegratefully

acknowledgethesupportbytheIsraeliScienceFoundation,theMinervaFoundation,theGerman-IsraeliFoundationforscientificresearch,theCrownPhotonicsCenter,andM.KushnerSchnur,Mexico.

SupplementaryMaterials

/cgi/content/full/339/6124/1187/DC1MaterialsandMethodsFigs.S1toS4

3September2012;accepted2January201310.1126/science.1229650

17.

ATransformingMetalNanocompositewithLargeElasticStrain,LowModulus,andHighStrength

ShijieHao,1LishanCui,1*DaqiangJiang,1XiaodongHan,2*YangRen,3*JiangJiang,1

YinongLiu,4ZhenyangLiu,1ShengchengMao,2YandongWang,5YanLi,6XiaobingRen,7,8XiangdongDing,7ShanWang,1CunYu,1XiaobinShi,1MinshuDu,1FengYang,1YanjunZheng,1ZeZhang,2,9XiaodongLi,10DennisE.Brown,11JuLi7,12*

Freestandingnanowireshaveultrahighelasticstrainlimits(4to7%)andyieldstrengths,

butexploitingtheirintrinsicmechanicalpropertiesinbulkcompositeshasproventobedifficult.Weexploitedtheintrinsicmechanicalpropertiesofnanowiresinaphase-transformingmatrix

basedontheconceptofelasticandtransformationstrainmatching.ByengineeringthemicrostructureandresidualstresstocouplethetrueelasticityofNbnanowireswiththepseudoelasticityofaNiTishape-memoryalloy,wedevelopedaninsitucompositethatpossessesalargequasi-linear

elasticstrainofover6%,alowYoung’smodulusof~28gigapascals,andahighyieldstrengthof~1.65gigapascals.Ourelasticstrain-matchingapproachallowstheexceptionalmechanicalpropertiesofnanowirestobeexploitedinbulkmaterials.tischallengingtodevelopbulkmaterialsthatexhibitalargeelasticstrain,alowYoung’smodulus,andahighstrengthbecauseoftheintrinsictrade-offrelationshipsamongtheseprop-erties(1,2).AlowYoung’smodulusinasingle-phasematerialusuallymeansweakinteratomicbondingandthuslowstrength.Becauseoftheinitiationofdislocationactivityand/orearlyfail-urecausedbystructuralflaws,theelasticstrainofbulkmetalsisusuallylimitedtolessthan1%.Becausefreestandingnanowireshaveultrahighelasticstrainlimits(4to7%)andyieldstrengths(3–9),itisexpectedthatcompositesmadewithnanowireswillhaveexceptionalmechanicalprop-erties.However,theresultsobtainedsofarhavebeendisappointing(10),primarilybecausethein-trinsicmechanicalpropertiesofnanowireshavenotbeensuccessfullyexploitedinbulkcomposites(10–12).AtypicalexampleistheNbnanowire–Cumatrixcomposite,inwhichthenanowiresare

nanowires,asillustratedinFig.1A.Second,SIMTanddislocationsliparefundamentallydifferentprocessesattheatomicscale.Whereastheinelasticshearstrainbetweentwoadjacentatomicplanesapproaches100%afterdislocationslip(17),theatomic-levelinelasticortransformationstrainis~10%afterSIMTintypicalSMAssuchasNiTi(16).Therefore,inelasticstrainincompatibilities(whichmustbecompensatedforbytheelasticstrainfieldtomaintaincohesion)aremuchmilderattheSMA-nanowireinterfacethanattypicaldislocation–piled-upinterfaces.

Toverifythishypothesis,weselectedNbnanowirestobecombinedwithaNiTiSMA.TheNiTi-Nbsystemwith~20atomic%Nbun-dergoeseutecticsolidificationintoamicrostruc-tureconsistingoffineNblamellae(18),whichcanbeconvertedintoNbnanowiresthroughse-vereplasticdeformation.Inthisstudy,aningotwithacompositionofNi41Ti39Nb20(atomic%)waspreparedbymeansofvacuuminduction

StateKeyLaboratoryofHeavyOilProcessing,ChinaUni-versityofPetroleum,Beijing102249,China.2InstituteofMicrostructureandPropertiesofAdvancedMaterials,BeijingUniversityofTechnology,Beijing100124,China.3X-raySci-enceDivision,ArgonneNationalLaboratory,Argonne,IL60439,USA.4SchoolofMechanicalandChemicalEngi-neering,TheUniversityofWesternAustralia,Crawley,WA6009,Australia.5StateKeyLaboratoryforAdvancedMetalsandMaterials,UniversityofScienceandTechnologyBeijing,Beijing100083,China.6SchoolofMaterialsScienceandEn-gineering,BeihangUniversity,Beijing100191,China.7StateKeyLaboratoryforMechanicalBehaviorofMaterialsandFrontierInstituteofScienceandTechnology,Xi’anJiaotongUniversity,Xi’an710049,China.8FerroicPhysicsGroup,NationalInstituteforMaterialsScience,Tsukuba,305-0047Ibaraki,Japan.9StateKeyLaboratoryofSiliconMaterials,ZhejiangUniversity,Hangzhou310058,China.10DepartmentofMechanicalEngineering,Uni-versityofSouthCarolina,Columbia,SC29208,USA.11Depart-mentofPhysics,NorthernIllinoisUniversity,DeKalb,IL60115,USA.12DepartmentofNuclearScienceandEngineeringandDepartmentofMaterialsScienceandEngineering,Massachu-settsInstituteofTechnology,Cambridge,MA02139,USA.*Towhomcorrespondenceshouldbeaddressed.E-mail:lishancui63@(L.C.);xdhan@(X.H.);ren@aps.anl.gov(Y.R.);liju@mit.edu(J.L.)

1

I

welldispersedandwellaligned,withstronginter-facialbonding.TheelasticstrainlimitachievedintheNbnanowiresinthistypeofcompositeisonly~1.5%(13,14),farbelowwhatmaybeex-pectedoffreestandingnanowires(3–9).

Tooptimizetheretentionofnanowireprop-ertiesinacomposite,wehypothesizethatthematrixshouldnotdeformviasharpmicroscopicdefectssuchascracksordislocationsbutrathershouldberubberyorgluelike,whichsuggeststheuseofashape-memoryalloy(SMA)asthematrix.TherearetwomaindifferencesbetweenanSMAmatrixandaconventional,plasticallyde-formingmetalmatrix.First,macroscopically,SMAsupportsalargepseudoelasticstrainof~7%bystress-inducedmartensitictransformation(SIMT)(15,16),whichisastrainmagnitudecomparabletonanowireelasticity(3–9).UseofanSMAasthematrixallowsonetomatchthehighpseudo-elasticityoftheSMAwiththehighelasticityof

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