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1、VOLUME89,NUMBER13PHYSICALREVIEWLETTERS23SEPTEMBER2002AdaptiveHomodyneMeasurementofOpticalPhaseMichaelA.Armen,*JohnK.Au,JohnK.Stockton,AndrewC.Doherty,andHideoMabuchiNormanBridgeLaboratoryofPhysics12-33,CaliforniaInstituteofTechnology,Pasadena,California91125(Received1April2002;publ
2、ished4September2002)Wepresentanexperimentaldemonstrationofthepoweroffeedbackinquantummetrology,confirmingthepredicted[H.M.Wiseman,Phys.Rev.Lett.75,4587(1995)]superiorperformanceofanadaptivehomodynetechniqueforsingle-shotmeasurementofopticalphase.Formeasurementsperformedonweakcoheren
3、tstateswithnopriorknowledgeofthesignalphase,adaptivehomodyneestimationapproachesclosertotheintrinsicquantumuncertaintythananyprevioustechnique.Ourresultsunderscoretheimportanceofreal-timefeedbackforreachingquantumlimitsinmeasurementandcontrol.DOI:10.1103/PhysRevLett.89.133602PACSnu
4、mbers:42.50.Dv,03.65.Ta,03.67.–a,06.90.+vQuantummechanicscomplicatesmetrologyintwoofachievingULestimationoftrueopticalphase(ascomplementaryways.Firstitforcesustoaccepttheopposedtophase-quadratureamplitude),forcoherentorexistenceofintrinsicuncertaintyinthevalueofobserv-anyotherpures
5、tatesofanopticalfield.ablessuchastheposition,momentum,andphaseofanInthisLetterwepresentanexperimentaldemonstra-oscillator.Suchquantumuncertaintyexistsevenwhenthetionofthesurprisingefficacyofreal-timefeedbackinthestateofthesystembeingmeasuredhasbeenpreparedinadevelopmentofULmeasuremen
6、tprocedures.Wedothistechnicallyflawlessway.Eventhevacuumstateofainthecontextofmeasuringtheopticalphasesofweaksingle-modeopticalfield,forexample,exhibits‘‘zero-pulsesoflight,followingatheoreticalproposalbypoint’’fluctuationsintheamplitudesofitselectricandWiseman[4].Thismetrologicaltask
7、canbemotivatedmagneticcomponents.Thesameistrueoftheopticalbyacoherentopticalcommunicationscenarioinwhichcoherentstatesrepresentativeoftheoutputofanidealinformationisencodedinthephaseoflaserpulsesthatlaser.Theseuncertaintieslimitthesensitivityofubiqui-musttravellongdistancesbetweent
8、hesenderandre-tousmeasurem
