Do you have an eye for entanglement

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1、Doyouhaveaneyeforentanglement?TakingagoodlookatcloningExperimentsthatrevealtheweirdnessofthequantumworldusuallyinvolvepreciseandhighlyspecializedequipment.ButnowphysicistsinSwitzerlandandtheUKhaveproposedawayofusinghumanvisiontoobservethepurelyquantumeffectof"entangle

2、ment".Theexperiment—whichhasyettobeperformedinthelab—wouldinvolveentanglingapairofphotonsandthencreatingthousandsofidenticalcopiesofoneofthepairsuchthattheycouldbeseenbythehumaneye.Entangledparticleshaveamuchstrongerrelationshipthanthatallowedbyclassicalmechanics.Fore

3、xample,thepolarizationofonephotonisrevealedinstantlybymeasuringthepolarizationitsentangledpartner,regardlessofthedistancebetweenthephotons.Thenewexperiment,whichhasbeenproposedbyNicolasGisinandcolleaguesattheUniversityofGenevaandUniversityofBristol,wouldfirstinvolvecr

4、eatingapairofentangledphotons.Thiscouldbedone,forexample,bypassinglightthroughanon-linearcrystalinwhichahigher-energyphotonisabsorbedfollowedbytheemissionoftwolower-energyphotons(arXiv:0902.2896).CloningphotonsOneofthephotonsisthen“cloned”tocreatethousandsofidenticalp

5、hotons.Thisisdonebystimulatedemission—thesameprocessbehindalaser—wherebytheoriginalphotonissentthroughapumpedopticalmedium.Becausetheclonesarecreatedinacoherentquantumprocess,itproducesapulseoflightthatisintenseenoughtobeseenwiththenakedeye—yetisentangledwiththesecond

6、originalphoton.Measuringthepolarizationofthepulsewillthereforerevealthepolarizationofthesecondphoton.Theteamproposestomeasurethepolarizationofthepulsebypassingitthroughapolarizingfilter,whichallowslightwithparallelpolarizationtopassthroughwhiledeflectinglightwithperpe

7、ndicularpolarizationby90°.Twohumanobservers—onelookingalongtheparallelpathandtheothertheperpendicularpath—couldthendeterminethepolarizationofeachpulse.Meanwhile,thepolarizationofthesecondphotonofthepairwouldbedeterminedbypassingitthroughasimilarpolarizingfilterthatism

8、onitoredbytwosensitivephotondetectors.PredictingtheoutcomeIftheexperimentisasuccess,thehumansshouldbeabletopredicttheoutcome