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I Sequential measurements

  1. Jul 22, 2017 #1
    I'd like to understand and know actual examples of how sequential measurements of different observables (position, energy, charge, etc.) in the same molecules can affect them giving rise to changes in the IR and Raman spectroscopy data. For example.. when you sequentially measure the molecules self energy and position, would it influence the electron cloud or the polarization or the dipole moment?
     
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  3. Jul 24, 2017 #2

    blue_leaf77

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    Spectroscopic measurement, regardless of what kind of method is used, is always the result of detecting photons emitted/absorbed by millions of molecules which are typically at random energy distribution centered around a value determined by the temperature. If you, e.g. measure the energy, I think the output of the measurement will have a very similar energy distribution and the spectrum will only exhibit negligible change.

    Molecule's position is directly related to the center of mass coordinate which can always be separated (factored out) from the relative coordinates. Because of this reason, measurement of the molecule's (center of mass) position will not affect the other observables which do not depend on the center of mass such as dipole moment, internal energy, etc.
    What is self energy?
     
  4. Jul 24, 2017 #3
    But according to Wikipedia https://en.wikipedia.org/wiki/Raman_spectroscopy

    "The Raman effect should not be confused with emission (fluorescence or phosphorescence), where a molecule in an excited electronic state emits a photon and returns to the ground electronic state, in many cases to a vibrationally excited state on the ground electronic state potential energy surface."
    "The Raman effect is based on the interaction between the electron cloud of a sample and the external electrical field of the monochromatic light, which can create an induced dipole moment within the molecule based on its polarizability. Because the laser light does not excite the molecule there can be no real transition between energy levels."

    What do you mean by center of mass coordinate of molecules? Any references about it?

    internal energy
     
  5. Jul 24, 2017 #4

    blue_leaf77

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    Where is the contradiction between the wikipedia article and that part of post #2.
    A molecule consists of multiple electrons and nuclei, you can always define a position variable which corresponds to the classical center of mass coordinate assuming the nuclei and electrons are point masses. Any classical mechanics book should cover this topic.
     
  6. Jul 25, 2017 #5
    Are you familiar with decoherence? They say when the Self-Hamiltonian dominates the evolution of the system, the preferred states will be energy eigenstates. Here there will be no position. How do you make the Self-Hamiltonian dominate the evolution of the molecules such that they will only have energy eigenstates and the position variable will cease to exist?

    Furthermore I was initially asking what would happen if you make the molecules become only energy eigenstates without any position and sequentially (in separate measurements) you make position dominates in the molecules. Would you have changes in the spectroscopy data between the two observables? What do you think?
     
  7. Jul 25, 2017 #6

    blue_leaf77

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    When you say "position dominates" do you mean you are measuring the molecule's position as a whole such that when you do this measurement twice first at ##(x_1,y_1,z_1)## and then at ##(x_2,y_2,z_2)## the molecule is just displaced?
    Sorry I am not familiar with some terms you used, especially the self-Hamiltonian.
     
  8. Jul 25, 2017 #7
    self-Hamiltonian is simply the energy eigenstates of the molecules. About position dominates. Take an atom and electron. If you measure the energy of the electron.. it ceases to have position.. whereas if you measure the position (or position dominates), it will have position. I was asking if it is possible to make position disappear in the molecules.. but then I realize phonons or any molecular vibration can give its position.. so maybe we have to cool it to absolute zero.. but there is still movement in terms of the zero point field. Maybe we can ignore this like we ignore the zero point field of the electron such that the electron ceases to have position? I was imagining what if we could remove all positions of all molecules, then perhaps we can teleport a living system to another place (since it has no position). But I guess we can't remove positions.. sad thing but maybe we just need to accept.
     
  9. Jul 25, 2017 #8

    blue_leaf77

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    When you measure an observable A that is not compatible with an observable B, it's not right to say then that this system doesn't have the observable B because what happens is just that after measurement of A the system can be found in a couple of values of B each with certain probability. When you measure the energy, the system will still have a valid position observable but now it's probability distribution equals the modulus of the eigenfunction in which the previous energy measurement resulted.
    This issue falls under the coverage of entanglement. Yet even if you use this, only the state/information that is teleported not the system itself. In fact you need an identical matter in the destination that will act as a receiving vessel for the state that you are teleporting.
     
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