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Electron Exclusion via EIT/CPT?

  1. Jan 6, 2013 #1

    jaketodd

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    With Electromagnetically Induced Transparency/Coherent Population Trapping, is it possible to prevent an atom or molecule from gaining an electron, given that the energy the electron would add to the atom or molecule is covered by the window of transparency/dark state?

    Thanks,

    Jake
     
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  3. Jan 7, 2013 #2
    First of all what do you mean by "gaining an electron", do you actually mean producing a negatively charge ion?

    Secondly, even though I didn't fully understand what you meant, I think the answer to your question is no, the EIT/CPT effect does not prevent such things. The reason would be that the EIT effects are coherent effects, they require the atoms to be in such a phase (dark state) that the light does not affect it. This superposition state cannot be obtained only be adding (or removing) energy, one also have to control the phase of the light/atoms correctly. By adding an electron, I see no way to control the phase of the of the state, or indeed even to accurately create a specific superposition at all.
     
  4. Jan 7, 2013 #3

    jaketodd

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    1) It doesn't have to be an ion; just gaining an electron.
    2) I don't see why you couldn't exclude the state that is represented energetically by gaining an electron.
    3) The addition of the electron is not part of the EIT/CPT. Instead, it is prevented from happening by its presence in the atom (its energy contribution to the atom) being driven to a probability of zero.

    Thank you Zargon, but would anyone else care to answer this question?

    Thanks!

    Jake
     
    Last edited: Jan 7, 2013
  5. Jan 7, 2013 #4

    mfb

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    I agree with Zarqon. I see no way how you could exploit a specific phase relation between different states to prevent electrons to be added. I cannot exclude it, however.
     
  6. Jan 7, 2013 #5

    jaketodd

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    Anyone else then please?

    It seems to me that a three-level system could be under Lambda EIT/CPT, and the transparency would prevent the transition from the first to the third state, assuming here that the transition requires the addition of an electron.

    Every time you add an electron to an atom or molecule, there is a change in energy. For example, see this picture. You can see the energy changes for each electron added.

    Now what I'm saying is that you could take a three-level system, and make transparent/trap the atom or molecule such that the energy change when adding another electron, like in the diagram, is not possible. Doesn't that make sense?
     
  7. Jan 7, 2013 #6

    mfb

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    There is no single state "atom+free electron", you have a continuum.

    meV<->GHz don't look like ionization energies to me.
     
  8. Jan 7, 2013 #7

    jaketodd

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    But there are states of "molecule with X electrons," and "molecule with X+1 electrons." Making the transition between those two states transparent seems doable. From the diagram, all it seems that need be done is pick three states, and make transparent the transition from how many electrons you already have in one state, to the state with one + that number of electrons. The resonances are given by the labeled energy amounts for the transitions as the molecule gains electrons on the diagram. For EIT/CPT, it's not required that all three states be populated.
     
  9. Jan 7, 2013 #8

    mfb

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    Sure, but there is no transition between them, as you cannot create electrons - at least not without (unbounded) positrons, where you would get the same problem again.
     
  10. Jan 7, 2013 #9

    jaketodd

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    Of course there is a transition, and no you don't need positrons! There is an energetic transition between a molecule with, for example, 5 electrons going to 6 electrons. Doesn't the diagram make that pretty clear?

    Thanks,

    Jake
     
  11. Jan 7, 2013 #10

    mfb

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    No. There is an energetic transition between a molecule with 6 electrons and a molecule of 5 electrons PLUS a free electron. And they don't have a discrete difference in energy.

    I am not sure how to interpret your diagram without any context, but I think it shows how energy levels of certain orbitals change depending on other electrons, or something similar. It does not show "ionization has a fixed transition energy of X" (the energy scale would be too low for that anyway).
     
  12. Jan 7, 2013 #11

    jaketodd

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    Ok, I think I see the point of confusion: I am not saying there is one energy increment for adding an electron to a molecule regardless of how many electrons it already has. No, I am saying that as you add electrons to a molecule (with different energetic changes for each electron added), different quantum states for the molecule are being created. And, doesn't it then follow that if you interact properly with these different states, in a manner consistent with EIT/CPT, then it would be possible to create a transparency/dark state for one of these quantum molecular states? And, to use your words, "energy levels of certain orbitals" are perfect candidates for EIT/CPT. Right?
     
    Last edited: Jan 7, 2013
  13. Jan 7, 2013 #12

    jaketodd

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    The question becomes: Can you make a molecule transparent to gaining an electron by making transparent/dark-state the orbital energy level configuration that the electron would create if integrated into the molecule? Once again, here is a diagram for O2

    I'd like to open this question up to anyone who can shed some light on this.

    Thanks,

    Jake
     
  14. Jan 8, 2013 #13
    Do you want to use optically created dark states? This is not how EIT works. As I mention in my first post, the trick is the relative phase between the light and the electron distribution of the atom. The EIT effect is not inherent in only the atom by itself, it appears only together with very specific light, and what it does is that it allows the light to pass through without interaction. To put it in other words: The atom is only in a dark state with respect to the Electric-field operator that created it.

    It is not inconcievable that one could create a similar effect with absorbing electrons as you want, but this would be a totally different ballgame, where the superpositions would be in the electron absorption regime and where the preparation of the phase of the dark state would have to be done with electrons with well controlled wavefunction phases. You cannot use an optically created dark state, for the reasons mentioned above. And how to control the phase of an electron wave function with sufficient accuracy I have no idea.
     
  15. Jan 8, 2013 #14

    mfb

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    That is not the point.

    To get a transition of specific energy, you need an electron wave (thanks Zarqon, good idea) - and to get EIT, you have to control its phase as well.
     
  16. Jan 8, 2013 #15

    jaketodd

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    Why can't the energy level changes (due to absorbing an electron) in the molecule be subjected to EIT/CPT, and that work? You guys are saying cancel out the possibility of the electron itself, and I am saying cancel out the effect the electron would have on the molecule. It seems to me if you lock the door to the home an electron would have in a molecule, then the electron would not be able to settle into place, and instead pass by.

    A good example is hypothetically starting with an O2 molecule with 5 electrons, and let's say you want to prevent it from getting a 6th electron. All you need to do, to "lock the door to the home" of that 6th electron, is make transparent the 62 GHz transition found here.

    Thanks,

    Jake
     
    Last edited: Jan 8, 2013
  17. Jan 8, 2013 #16

    mfb

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    It does not help to make it transparent to that light. The electron simply does not care, it can catch an electron and emit a photon of 62 GHz with some phase you cannot control, probably together with another photon related to the new electron. Maybe both energy differences are combined and a single photon is emitted, I don't know.
     
  18. Jan 8, 2013 #17

    jaketodd

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    I'm having difficulty understanding this post. Please address the idea of canceling to zero the probability of the quantum state of the energy levels with a 6th electron. In your post, you say that the molecule would emit photon(s), one of which might be of the energy level configuration energy of 62 GHz. I don't see why such an emission would occur. Once again you're talking about the electron ("The electron simply does not care..."), when I am talking about applying EIT/CPT to the energy level configuration, populated by electrons, in the molecule

    Confused,

    Jake
     
  19. Jan 8, 2013 #18

    jaketodd

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    To simplify: You're still talking about rendering an EIT/CPT effect on the electron itself, when I am talking about the much-less-energetic "home" the 6th electron would have in the molecule. I am talking about rendering EIT/CPT on the energy level configuration; not on the electron itself. Without its place to settle, the electron cannot join the molecule.
     
  20. Jan 8, 2013 #19

    jaketodd

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    I'm going to start another thread with a similar question. Thank you for your help thus far. I would like this thread to continue. I'll put the new one in the Quantum Physics category just like this one.

    Jake
     
    Last edited: Jan 8, 2013
  21. Jan 9, 2013 #20
    I'm pretty sure the crucial point that makes you confused is that you don't realize that a "dark state" is simple a completely normal superposition state, there's nothing magical or special to it. And there is no reason why an atom or molecule in a normal superposition state could not absorb an electron (if the situation at large is such that it could).

    A dark state only becomes dark when paired with the light (of the right phase) that created it. The dark state is atom PLUS light, not the atom by itself, and thus you cannot "close the door" on the atom, because you only close it for that particular light, not for any other light, and not for electrons.

    For further experimental proof of this, see the typical EIT spectra. The transmission peaks in EIT spectra (where the atom is dark) are typically very narrow. This means that light at just a slightly different frequency than what created it, is NO LONGER a dark state. It should then be obvious that something completely different, like electrons are definately not going to see a dark state.
     
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