Photon

Thedevelopmentofphotons

Theproposalanddevelopmentofphotons—thequantumtheoryoflight

In1901,GermanphysicistPlanck(Plank)foundtheenergydistributionlawoftheabsoluteblackbodyradiationspectrumunderthermalequilibriumconsistentwiththeexperiment.Thislawisthestartingpointforthedevelopmentofquantumtheory.Thebasisofthislawistoassumethatmatterhasdiscontinuouscharacteristicsoflightemittedandabsorbed,andthatlightisemittedorabsorbedbyafinitepart-lightquanta.

Theenergyεofthisphotonisproportionaltothevibrationfrequencyωoflight,andcanbeexpressedbythefollowingequation

Here

WhenEinsteinpointedoutthatinadditiontoenergyε,animpulse(thedirectionofthisimpulseisconsistentwiththepropagationdirectionoflight)mustbeusedtodescribethephoton,thephotonTheexpressionhasonlygotaperfectform.

Ifthewavevectork,isintroduced,itscomponentisequalto

whereλisthewavelength,andcosα,cosβ,cosγIsthecosineofthenormaldirectionofthelightwave,sotheimpulseformulaofthelightquantumcanbewritteninvectorform

photonaction

photonisTheelementaryparticlethattransmitselectromagneticinteractionisagaugeboson.Photonisthecarrierofelectromagneticradiation,andinquantumfieldtheory,photonisconsideredasthemediatorofelectromagneticinteraction.Comparedwithmostelementaryparticles,therestmassofaphotoniszero,whichmeansthatitspropagationspeedinvacuumisthespeedoflight.Likeotherquanta,photonshavewave-particleduality:photonscanshowthepropertiesofclassicwavessuchasrefraction,interference,anddiffraction;andtheparticlenatureofphotonscanbeprovedbythephotoelectriceffect.Photonscanonlytransmitquantizedenergy.Theyarelatticeparticlesandthemass-energyphaseofcirclequantumparticles.

Photonproperties

Aftertheestablishmentofquantumelectrodynamics,itisconfirmedthatphotonsarethemediaparticlesthattransmitelectromagneticinteractions.Chargedparticlesinteractbyemittingorabsorbingphotons.Thepairofpositiveandnegativechargedparticlescanbeannihilatedandconvertedintophotons,andtheycanalsobegeneratedinanelectromagneticfield.

Photonsareparticlesthatcarryenergyinlight.Theenergyofaphotonisproportionaltothefrequencyofthelightwave.Thehigherthefrequency,thehighertheenergy.Whenaphotonisabsorbedbyanatom,anelectrongainsenoughenergytotransitionfromtheinnerorbittotheouterorbit,andtheatomwiththeelectronictransitionchangesfromthegroundstatetotheexcitedstate.

Photonshaveenergy,momentum,andmass.Accordingtothemass-energyequation,E=mc²=hν,findm=hν/c²,

Becausethephotoncannotbestationary,ithasnostationarymass.Themasshereistherelativisticmassofthephoton.

Accordingtoquantumfieldtheory,apairofpositiveandnegativeparticlescanbeannihilatedintoapairofhigh-energygammaphotons,andapairofhigh-energygammaphotonscanalsoreactathightemperaturestoproduceapairofpositiveandnegativeparticles.Forexample,atatemperatureofT=10¹⁵K,theconversionofphotonsintobaryonssuchasprotonsandneutronscanoccur.

Thepositron-negativeelectronscattering(alsocalledBha-Bhascattering)representedbyFeynmandiagram,andthewavylinerepresentstheprocessofexchangingvirtualphotons.

See:SpecialTheoryofRelativity

Fromtheperspectiveofwaves,photonshavetwopossiblepolarizationstatesandthreeorthogonalwavevectorcomponents,whichdetermineFromthepointofviewofparticles,therestmassofthephotoniszero,thechargeiszero,andthehalf-lifeisinfinite.Aphotonisagaugebosonwithaspinof1,sothenumberofleptons,baryons,andsingularnumbersareallzero.

Therestmassofthephotonisstrictlyzero,whichisessentiallyequivalenttothestrictinversesquaredrelationshipofCoulomb'slaw.Iftherestmassofthephotonisnotzero,thenCoulomb'slawisnotstrictlytheinversesquarelaw.Allrelatedclassicaltheories,suchasMaxwell'sequationsandtheLagrangianquantityofelectromagneticfields,relyontheassumptionthatthestaticmassofphotonsisstrictlyzero.FromEinstein’smass-energyrelationshipandphotonenergyformula,theupperlimitofphotonmasscanberoughlyobtained:m=hν/c²

Here,mistheupperlimitofphotonmass,andνisthefrequencyofanyelectromagneticwave,whichistheSchumannresonanceintheultra-lowfrequencyband.Thelowestknownfrequencyisabout7.8Hz(Hertz).

Thisvalueisonlytwoordersofmagnitudehigherthanthecurrentlyacceptedupperlimit.

SeePhotons:CanonicalBosons

Photonscanbeproducedinmanynaturalprocesses,forexample:inmolecules,atomsornucleifromhighenergylevelstolowenergyPhotonsareradiatedwhenthechargeisacceleratedduringtheleveltransition,andphotonsarealsoproducedwhenparticlesandantiparticlesareannihilated;intheabove-mentionedtimereversalprocess,photonscanbeabsorbed,thatis,molecules,atomsornucleitransitionfromlowenergylevelstohighenergylevels,Thegenerationofparticleandantiparticlepairs.

Thespeedofphotonsinvacuumisthespeedoflight,andtherelationshipbetweenenergyEandmomentumpisp=E/c;Theenergy-momentumrelationshipofparticleswithstaticmassinrelativisticmechanicsis.

Theenergyandmomentumofthephotonisonlyrelatedtothefrequencyνofthephoton;oritisonlyrelatedtothewavelengthλ.Thus,themomentumofthephotonisobtainedasp=h/λ=hv/c.

wherehiscalledPlanck'sconstant.

Aninferencecanbederivedfromtheenergyandmomentumformulasofphotons

Theannihilationprocessofparticlesandtheirantiparticlesmustproduceatleasttwophotons.Thereasonisthatthetotalmomentumofthesystemcomposedofparticlesandtheirantiparticlesinthecenterofmasssystemiszero.Duetothelawofconservationofenergy,thetotalmomentumofthegeneratedphotonsmustalsobezero;becauseasinglephotonalwayshasanon-zeromomentum,thesystemOnlytwoormorephotonscanbegeneratedtosatisfythetotalmomentumofzero.Thefrequencyatwhichphotonsareproduced,thatis,theirenergy,isdeterminedbythelawofconservationofenergy-momentum(four-dimensionalmomentumconservation).Fromtheconservationofenergy-momentum,itcanbeseenthattheinverseprocessofparticleandantiparticleannihilation,thatis,theprocessoftwo-photongeneratingelectron-antielectronpairscannotbespontaneouslygeneratedinavacuum.

Photonhaswave-particleduality

Thatistosay,photonnotonlyhasthecharacteristicsofoneparticlebyoneparticle,butalsohasthevolatilitylikesoundwave.Whentimeisaninstantaneousvalue,photonspropagateintheformofparticles;whentimeisanaveragevalue,photonspropagateintheformofwaves.Thewavenatureofphotonsisprovedbythediffractionofphotons,andtheparticlenatureofphotonsisprovedbythephotoelectriceffect.

Somepeopleabovethinkthatitiswrongforthephoton'sdynamicmasstobezero,andthephoton'sstaticmassiszero,otherwiseitsdynamicmasswillbeinfinite.Butitsdynamicmassdoesexist.Thecalculationmethodisasfollows:First,sincetheenergyofthephotonwithfrequencyvisE=hv,(WherehisPlanck'sconstant),soitsmasscanbeobtainedfromthemass-energyformula:m=E/c²=hv/c²wherec²representsthesquareofthespeedoflight.ThismethodwasfirstproposedbyEinstein.

PhotonTheory

Photonshavespeed,energy,momentum,mass,andcondensation.Itisimpossibleforphotonstostandstill.Photonscanbecomeothersubstances(suchasapairofpositiveandnegativeelectrons),butenergyandmomentumareconserved.[Withinafewnanoseconds)controlthepathandpolarizationofphotonswiththesamewavelengthasthecurrentopticalcommunicationnetwork.Thenewphotoniccircuitcanbeintegratedintotheexistingopticalcommunicationnetwork,therebysignificantlyimprovingtheperformanceofthenetwork.Thelatestresearchhastakenasteptowardstherealizationofopticalquantumcommunication.

ScientistsfromtheUniversityofBristol,Heriot-WattUniversity,andtheKavliInstituteforNanoscienceintheNetherlandspublishedthisstudyontherapidcontrolofthepathandpolarizationofsinglephotonsinthelatestissueofPhysicalReview"LearningExpress"magazine.

Whentheystudiedaquantumopticaldevicecomposedofcircuits,theyfoundthatasinglephotonwouldmovethroughthesecircuits,andthesecircuitscouldalsobereconfiguredtochangethepathandpolarizationdirectionofthephoton.However,suchquantumopticalcircuitscannotquicklymanipulatesingle-photonandmulti-photonstates.Inordertosolvethisproblem,theyusedalithiumniobatewaveguidethathasbeenproventobecapableofrapidmanipulationinexistingcommunicationmodulators,andprovedthatapplyingavoltagetothewaveguideneartheelectrodecanquicklymanipulateoneortwowavelengthsof1550nanometers.Thequantum(includingpathandpolarization)stateoflightcomposedofaphotonisexactlythewavelengthusedintheexistingcommunicationnetwork.

DamienBonooftheUniversityofBristol,wholedtheresearch,said:“Inthisexperiment,wedemonstratedtwocircuitconfigurations.Eachcircuitconfigurationleadstoadifferentquantumstate.Configurationonlytakesafewnanoseconds.Inpreviousexperiments,thecircuitcanbereconfiguredeveryfewseconds.Communicationnetworksuseswitchesmadeofthesametechnologytotransmitinformationbytesencodedbyopticalpulseseveryday.Intermsoftheabove,suchaswitchcanalsobeusedatthesingle-photonlevel."

Bonosaid:"Uptonow,themanipulationofthequantumstateoflightonthechiphasalwaysreliedonheaters,whichcanbeusedasaslowphaseshifter.Thelatestresearchshowsthatthelithiumniobatewaveguidecanuseacompletelydifferentmethodtomanipulatethequantumstateoflightmorequickly.Wecannotonlyopenandclosetheopticalpackettosendtraditionalinformationaccordingtotheprescribedroute,butalsoQuicklyprocessandmanipulatethequantumstateoflight."

Scientistspointedoutthatbeingabletoquicklycontrolthepolarizationandpathofasinglephotononasingleplatformisveryimportanttobasicquantumscienceandquantumtechnology.Bonosaidthatthelithiumniobatematerialsusedtomakethesedevicescanalsorandomlygeneratephotons.Inaddition,single-photondetectorswithsuperconductivitycanalsobeintegratedonsuchachip.Atechnologyplatformthatcombineslightsources,circuits,anddetectorsthatcanrandomlygeneratephotonscanbeusedinthefollowingareas:multiplephotonsourcesareusedtoobtainreliablesingle-photonsources,quantumrelaysrequiredforlong-distancequantumcommunications,Quantumkeydistributionusedinquantumcryptography,etc.

Inthepast,someold-fashionedradiosusedelectronictubes,andtheyhadtobewarmedupeachtimetheyworked.Withtheapplicationofsemiconductortubes,thepreheatingtimeissaved.Nowadays,similaradvanceshavetakenplaceinthefieldofopticalquantummodulationequipment.Inthepast,aheaterwasusedtoreconfigurethecircuitinafewseconds,anditwaspossibletoswitchtoanothercircuitinafewnanoseconds.Theuseoflithiumniobateasawaveguidedeviceisacommontechnicalmethodinthemodemera.Butwhowouldhavethoughtthataslightchangeinthemediocrephotoelectricconversionequipmentcouldhelpthemostcutting-edgeopticalquantumcommunicationresearchtomakeabreakthrough?Withtheintegrationoflightsources,circuits,anddetectors,theworkloadofquantumcommunicationresearcherscanbereducedalot.

Relatedevents

ProfessorsofHuazhongUniversityofScienceandTechnologyredefinetheupperlimitofphotonrestingmass

ProfessorsofHuazhongUniversityofScienceandTechnologyredefinetheupperlimitofphotonrestingmassSomepeopleintheindustrybelievethatthezerorestmassofphotonsisoneofthebasicassumptionsofclassicalelectromagnetictheory.Butsomescientistsbelievethatphotonsmayhaverestmass.Iftheexperimentfinallydetectsthatthephotonhasarestmass,thensomeclassicaltheorieswillhavetochange.

IntheAmerican"PhysicalReviewLetters"(PhysicalReviewLetters),aspecialarticleintroduced:"AnewexperimentcompletedbyChinesescientistLuoJunandothersshowsthatunderanycircumstances,Therestmassofaphotonwillnotexceed10totheminus54kilogram.Thisresultis1/20ofthepreviouslyknownupperlimitofphotonmass.”LuoJunandhiscolleaguesusedanovelexperimentalmethodtoexperimentinacave.Theupperlimitoftherestingmassofphotonsintheroomhasbeenfurtherincreasedbyatleastanorderofmagnitude.

Itisreportedthatifthephotonhasastaticmass,althoughitwillnotaffectpeople’sdailylife,theconsequenceswillbefundamental-forexample,thespeedoflightwillchangewiththechangeofwavelength,andLightwaveswillbeabletoproducelongitudinalvibrationsjustlikesoundwaves.