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Decoherence in EM field

  1. Dec 11, 2015 #1
    How do you treat decoherence in purely electromagnetic field? In other words, can EM field also have decoherence? How?
     
  2. jcsd
  3. Dec 11, 2015 #2

    bhobba

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    Decoherene is a general quantum phenomena that is exactly the same for EM as any other quantum objects.

    Thanks
    Bill
     
  4. Dec 11, 2015 #3

    Demystifier

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    Why do you think that EM field might not have decoherence?
    It certainly does. That's a reason why in some circumstances we see coherent or squeezed states, while in other circumstances we see photon-number eigenstates.
     
  5. Dec 11, 2015 #4
    In electrons.. it's all particles so decoherence is just one particle against others.

    But in electromagnetic field.. is decoherence about particle and the em wave.. but the em wave is not the wave function of the photon.. so what is decoherence with respect to?
     
  6. Dec 11, 2015 #5

    bhobba

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    Everything is a quantum field. Its more complex in QFT but the principles are exactly the same:
    http://arxiv.org/pdf/hep-th/9508052v1.pdf

    Note - my knowledge of QFT is not good enough to go into the detail of it - but being a quantum theory it must have decoherence - its an inevitable consequence of entanglement which is foundational to QM.

    Thanks
    Bill
     
  7. Dec 11, 2015 #6

    Demystifier

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    So basically, you ask what replaces the wave function in quantum field theory? Instead of wave function you have a wave functional, which can be thought of as wave function depending on an infinite number of "coordinates".
     
  8. Dec 11, 2015 #7
    What I was inquiring was whether you use photons as particles in the decoherence in electromagnetic wave or whether you use wave.

    In conventional QM, you use particles like electrons in the measurements.. and the system and environment are models in terms of particles.. how about in electromagnetic wave? Can you give an example of decoherence in em wave with system and environment in the factorization (or decomposition)?
     
  9. Dec 11, 2015 #8

    bhobba

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    You use neither - its an 'ecitation' of the EM field - not particle or wave. Even in ordinary QM it neither particle or wave.

    We can use photons to decohere and do a measurement eg a few stray photons from the CBMR is enough to give a dust particle a definite position.

    Thanks
    Bill
     
  10. Dec 12, 2015 #9
    Docoherence occurs when there is observational apparatus and say entangled photons. Im asking would there be decoherence if the observational apparatus is purely em wave and not any particle? I'm trying to get my head of pure em wave decohering other em waves.
     
  11. Dec 12, 2015 #10

    bhobba

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    Last edited by a moderator: May 7, 2017
  12. Dec 12, 2015 #11
    but the context of it came from you yourself. reading about decoherence i saw this post of yours where you stated

    "The system here is not the entangled electrons - its the entangled electrons AND the observational apparatus - that's where the decoherence occurs. It is the interaction with the observational apparatus that transforms the superposition of the up/down spin to a mixed state and breaks the entanglement with the other electron."

    i was simply asking whether the observational apparatus can be pure em wave?

    i have browse your reference at the library. i just wanted to know how do you deal with pure em wave decoherence?
     
  13. Dec 12, 2015 #12

    bhobba

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    You hit it in one with the word - CONTEXT.

    I was undoubtedly speaking to a particular situation - in general decoherence has nothing to do with electrons and observational apparatus. Its to do with a general quantum phenomena independent of that.

    As I said photons interact only weakly so you don't have pure em wave decoherence.

    Thanks
    Bill
     
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