Entanglement I 13

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  • 8/9/2019 Entanglement I 13



    byRobert Nemiroff

  • 8/9/2019 Entanglement I 13


    Physics X: About This Course

    Officially "Extraordinary Concepts in Physics" Being taught for credit at Michigan Tech

    o Light on math, heay on conceptso !nyone anyhere is elcome

    #o text$oo% re&uiredo 'i%ipedia, e$ lin%s, and lectures onlyo (ind all the lectures ith )oogle at*

    "+tarship !steris%" then "Physics "o http://bb.nightskylive.net/asterisk/viewforum.php?f=39

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: $%E&%'E(

    Two parti)les )an be )onsi*ere* entangle* when a +uantum state oftwo parti)les are linke*.

    ,an o))ur for parti)les that were-

    )reate* at the same pla)e an* time.- )olli*e* at some pla)e an* time.Typi)ally involves- spin- momentum

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: $'T&$N'0"

    ositronium- ele)tron an* a positron orbiting- *e)ays +ui)kly into two *aughter photons

    1aughter photons of ositronium haveo entangle* spins 2oppositeo entangle* momenta 2opposite

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    - 5936 paper by Einstein7 o*olsky7 an* &osen 2E&- Thought by E& to show that

    o 8" is in)ompleteo hi**en variables must eisto otherwise 8" spooky a)tion at a *istan)e

    - origin of entangle* parti)les i*ea

    - ;asis for ;ell

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    - imple version of E& eperiment:- A sour)e *e)ays into two parti)les 2entangle*

    o one goes to Ali)e 2A7 the other to ;ob 2;o the total angular momentum is >ero

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    'f Ali)e measures the spin of her parti)le to be spin up on the >ais7will Ali)e know that ;ob will measure his entangle* parti)le to be spin*own on the >ais before;ob knows it?

    5. @es7 Ali)e is that smart.. No7 that woul* re+uire BT! )ommuni)ation.3. @es7 but only in a statisti)al sense.C. 1epen*s on how mu)h Ali)e is paying her psy)hi).

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    5. @es7 Ali)e is that smart.

    'n fa)t7-

    'f Ali)e an* ;ob both measure > ais spino will A!(A@ get opposite > spin- 'f Ali)e an* ;ob both measure ais spin

    o will A!(A@ get opposite spin

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    1oes this7 by itself7 mean that Ali)e an* ;ob )an )ommuni)ate BT!?

    5. @es.. No.

    3. "aybe so.

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    . No.

    't )oul* be that the parti)les were )reate* ea)h having opposite spins.This )oul* have been *one with tennis balls this )orrelation re+uires

    only )onservation of momentum7 not BT! )ommuni)ation. Thatparti)les are )reate* with attributes that are then fro>en is part of thei**en %ariables 2% interpretation of +uantum me)hani)s.

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    Net7 Ali)e measures her parti)le as spin up on >ais an* ;obmeasures his parti)le>y.

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: E& A&A1$4

    3. alf the time spin up7 half the time spin *own.;ob measurement is in*epen*ent of Ali)e

  • 8/9/2019 Entanglement I 13


    ENTAN!E"ENT: !$,A!'T@

    The prin)iple of lo)ality states that obe)ts )an only be affe)te* by theirimme*iate surroun*ings.

    Entanglement appears to violate lo)ality but not in su)h a way that

    allows *istant observers to sen* information to ea)h other faster thanthe spee* of light.