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How does SPDC happen?

  1. Aug 29, 2016 #1
    I've been doing some reading about SPDC. I understand the wave mixing, the conservation laws, the coupled equations for the three fields (pump, signal and idle).

    But I can't find any good reference on how does the split happens? (how the two photons are created)

    Is it because photons of the pump interact with atoms in the crystal and get scattered?
    Is some kind of interaction with the grid?

    I really don't get this.

    The only hint I got is that it must be related with somethin called "two-mode squeezed vacuum".

    Can someone please explain this to me? or redirect me to a good reference where I can do my own reading?

    Thanks in advance :)
  2. jcsd
  3. Aug 30, 2016 #2
  4. Aug 30, 2016 #3

    Thank you very much. I have already read that. But it doesn't say how the pair is created.
  5. Aug 30, 2016 #4


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    it does
    but just how deep a description do you want ??

    if you want to go deeper how about googling your Q
    I googled " how does Spontaneous parametric down-conversion of photons occur ? "
    and there were many hits to professional papers
  6. Aug 30, 2016 #5
    I suppose deep enough to know what kind of interaction is involved in order to split the photon.

    Is it the crystal acting like a resonator?
    Is the photon exciting electrons in the atoms of the crystal?

    I don't get that part.

    Thanks for the answer.
  7. Aug 30, 2016 #6


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    am sure one or more of those many papers will have some good info :smile:

  8. Aug 30, 2016 #7


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    I'm going to guess any advanced explanation is going to involve QED. How much do you know about that?
  9. Aug 30, 2016 #8
    Thanks I'm reading the ones I have not read yet :)

    Not much really. I know quantum mechanics and electromagnetism quite well, but nothing of QED.

    My problem is, everyone describes SPDC as a process where a photon spontaneously splits into two photons. But I haven't yet read why the original splits? and how? That's the part I would like to understand.
  10. Aug 30, 2016 #9


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    Staff: Mentor

    I can't help you with that I'm afraid. That's well beyond my knowledge level. Hopefully your searches will come up with something if you can't get an answer here.
  11. Aug 31, 2016 #10
    Thank you very much. It seems like "Nonlinear Optics" by Boyd might have some answers :)
  12. Aug 31, 2016 #11

    Andy Resnick

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    It's important to note that the two photons are entangled- they are not independent objects. Parametric down-conversion is often the source used to generate entangled photons for quantum encryption keys. Parametric amplifiers can be used to generate many other non-classical states: for example, by tuning the signal to match the pump, the idler is the vacuum state. It's also possible to generate squeezed states.

    If Boyd isn't sufficient, there's a good chapter in Yariv's "Quantum Electronics" and several chapters in Mandel and Wolf's "Optical Coherence and Quantum Optics".
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