2022-2023学年高二物理竞赛课件：玻色-爱因斯坦凝聚

玻色-爱因斯坦凝聚

玻色-爱因斯坦凝聚一、理想玻色气体化学势的性质二、Ｎ与基态粒子数关键在于当时，将上的粒子数忽略了.解决办法:三、矛盾的原因与解决办法当时，该能级上的粒子数与总粒子数相比，可忽略；而时，该能级上的粒子数是很大的数值，不可忽略。1.01.00基态粒子比份T＞TC

弥散态T＜

TC

凝结态T＝

TC

相变点T

0

全部凝结玻色－爱因斯坦凝聚2.条件a.玻色子b.随温度而改变，且随温度降低趋向于01.现象：时，有宏观量级的粒子在零能级凝聚

玻色凝聚：μ

=0

,n0与n可比

●

●

●

●●●●●●●P=0级

●

●

●●●●●●●●弥散态(动量空间)凝聚态动量空间的凝聚现象,凝聚体的熵为零，对压强无贡献四、凝聚相下，内能由能量大于0的粒子决定玻色－爱因斯坦凝聚的实现(1)LowtemperatureT~10–9(e.g.Rb)

Coolingandtrappingatoms

(2)Higherdensityn~1011-12

Trappingatomsbyusinglaser(3)Systemkeepsinthegasphase

(Non-interaction)

TheNobelPrizeinPhysics1997"fordevelopmentofmethodstocoolandtrapatomswithlaserlight"StanfordUniv.

Stanford,CA,USA

b.1948CollègedeFranceandÉcoleNornaleSupérieureParis,Franceb.1933NationalInstituteofStandardsandtechnology,MD,USAb.1948Theirresearchishelpingustostudyfundamentalphenomenaandmeasureimportantphysicalquantitieswithunprecedentedprecision.ClaudeCohen-Tannoudji

StevenChu

WilliamD.Phillips1980swhenWilliamPhillipsdevelopednewmethodsofdeceleratingafastatombeam.In1985thefirstreportscamefromexperimentswherethemeanvelocityhadbeenreducedfrom1000m/stozero.DecelerationofAtoms

MOTThemostoftenusedforatomtrapistheMagneto-OpticalTrap(MOT).

StevenChu

usedDopplercoolingwiththreepairsofcounter-propagatinglaserbeams.Atom,regardlessofwhatdirectionitismoving,willencounterafrictionforceandthevelocityspread(andthetemperature)willbereduced

opticalMolasses.Acollectionofsodiumatoms(yellowdotinmiddleofpicture)trappedinaMOT.Lightactsmechanicallyonmaterialobjects,tochangetheirpositionsandvelocities.Laserreducesthevelocityspread(cooling),orconfinetheatoms(trapping).NewcoolingmechanismsExplanationsofthelowtemperatureswerefoundbyClaudeCohen-TannoudjiandbyStevenChu.GreekmythologyhasitthatSisyphusmustendlesslyrollastoneupahillintheUnderworld.Assoonashereachesthetopthestonerollsdownagain.Oneexampleofthenewcoolingmechanismsis

Sisyphuscooling,wheretheconceptsoflightshiftandopticalpumpingplayanimportantrole.

SisyphuscoolingCohen-Tannoudji

developedthefollowingphysicalpicture:10-6KTheatomsmoveonasinusoi-dallymodulatedpotentialsurface,whentheyinteractwithlight(lightshift).Whentheytravel'uphill'theylosespeed.Astheyreachthetopofthe'hill'theyareopticallypumpedtothebottomofa'valley'.Inthiswaytheatomswillalwaystravel'uphill',andthustheirvelocitywillgraduallybereduced.继续降温玻色凝结TheNobelPrizeinPhysics2001"fortheachievementofBose-Einsteincondensationindilutegasesofalkaliatoms,andforearlyfundamentalstudiesofthepropertiesofthecondensates"EricA.CornellUSAUniversityofColorado,JILA

Boulder,CO,USAb.1961WolfgangKetterleFRG

MIT,

Cambridge,MA,USAb.1957

CarlE.WiemanUSAUniversityofColorado,JILA

Boulder,CO,USAb.1951

Program

GetfirstlyagreatdealofBoseatomswithhighdensityandcooledtemperature(Lasercoolingandtrappingtechnology)Putthesampleinastaticmagneticwell(Magne