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Is there entanglement other than 50/50 energy? of the pump photon

  1. Jan 17, 2013 #1
    During the creation of entangled photons (say via SPDC as described, for example, at the bottom of this post):

    Do/can we also get photons that are say 60/40, 70/30 etc? ..if we remove/adjust the filter etc....

    i.e. the entangled photons are not exactly half the energy
    one of the entangled photons have 60% of the energy of the pump photon and
    the other entangled photon has 40% of the energy of the pump photon.

    What does that mean for, say, spin or momentum entangled photons?

    How would such photons behave? in experiments like

    1. double slit interference.....would we have modified/skewed interference pattern?
    2. Bell's experiments...i.e. would we have a 60-40 correlation between spins etc?
    3. Delayed choice quantum eraser etc.

    Last edited: Jan 17, 2013
  2. jcsd
  3. Jan 18, 2013 #2
    Non-linear optics is complicated, there are as many possible processes as you can imagine, and all of their time reversals. All have an associated wave vector(energy) conserving process, and only a few of them have equal energies for output photons.

    When the writer specifies the "type" of crystal, this is a polarization definition. It has to do with the crystal axis and how it projects the downconverted photons to ordinary (o) polarization or extraordinary (e) polarization. It's complicated, but wikipedia has a good intro.

  4. Jan 18, 2013 #3


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    Very good San! As Al says, there is conservation and there are many pairs produced that are not 50-50.

    Experimentally, this is often controlled by how the desired pairs are collected. Pump photons that are not down converted go straight through the crystal. These are normally not desirable for collection. Down converted pairs are produced off-angle! The angle of deflection is related to the amount of momentum they have. So certain deflection angles represent 50-50 splits.

    Generally 60-40 splits will still be polarization entangled although there may be a function whereby their fidelity is less. Not really sure.

    Here is a great reference that tells a lot about the process, from a top team:

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