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ID:49251701
大小:2.67 MB
页数:24页
时间:2020-02-02
《Bell_Measurements_and_Teleportation.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、BellMeasurementsandTeleportationOverviewEntanglementBellstatesandBellmeasurementsLimitationsonBellmeasurementsusinglineardevicesTeleportationDensecodingEntanglementswappingEntanglementpurificationQuantumrepeatersEntanglementTwosystemsdescribedbytwosepa
2、rableHilbertspaces.Statesofthetwosystemscanbedescribedbythetensorproductoftheirstatespaces.Schmidtdecomposition:Ifandthestateissaidtobeseparable.Ifmorethanonethenissaidtobeentangled.Thestateofonesystemcannotbespecifiedwithouttheother.BellStatesFortwotw
3、o-statesystemsdenotedeachbytheBellstatesformabasisforthewholesystemandaremaximallyentangled:whereisanti-symmetricandaresymmetricwithrespecttoparticleinterchanging.BellMeasurementsDistinguishingBellstatesusinglinearelementssuchasbeamsplitters,phaseshift
4、ers,photo-detectorsetc.Allelementscanbedescribedbyunitarytransformations.Inlinearonesparticlenumberisconserved.PolarizationbeamsplitterHalfwaveplateat45degreesExamplesforphotons:Beamsplitter:Example:distinguishinganti-symmetricandsymmetricstates-Hong–O
5、u–MandeleffectDoubletransmissionobtainsaminussignrelativetodoublereflection.symmetricstateshavezeroamplitudeford1-d2coincidence.d1+d2simultaneous“click”thestatehascollapsedtoBymeasuringtheBelloperatorwehavecreatedentanglement!Beamsplitteroperatorrepre
6、sentationforasinglephoton:OR?DistinguishingBellStatesThegoal:Tocreateasetofunitaryoperatorsthatwouldmakeadifferentsetofdetectors“click”foreachBellstate.DistinguishingBellstates–cont.Aschemetomeasure2+Bellstates.Turnsoutthisisthebestwecandowithlinearele
7、ments.Non-lineardevicescanachieveacompletemeasurementbutwithlowefficiency.TeleportationAlicewantstosendaquantumbittoBob.Shecannotmeasurethestateandsendtheresults.Ifshesendsthequbititselfitmightdeteriorateonthewayortaketoomuchtimetogetthereifitisastateo
8、famassiveobject.Teleportation–cont.Alicehasaphoton-qubitthatshewantstoteleport.Alicecreatestwoentangledphotons,2and3,andsendsphoton3toBob.SheperformsaBellmeasurementonphoton1andphoton2andsendsBobtheresult.Bobperformsatransformationofhis
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