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Thread: Quantum Entanglement

  1. #1
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    Default Quantum Entanglement

    This is an interesting watch...

    http://hackaday.com/2015/11/30/uses-...hanni-prutchi/

    Thoughts?
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  2. #2
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    I don't understand the reason for the added complexity in her "teleportation" branch of this experiment. It seems that it would be easy enough for any of us to largely recreate the synthesis of these entangled photons. BBO crystals are a lot less expensive than $1,000. The filtering out of "junk", non-linear products with the orthogonal crystals eludes me. Or, is the "junk" filtered out by its non-810nm wavelength? If so, then again, why the orthogonal crystals?

    Once there however, why not polarization rotate "A" with say a Pockels cell and read "B" by it's ability or inability to pass a fixed polarizing filter? The faster than light test would involve having to identify the delay in rotation of "A", measurement jitter, statistical noise and a robust null test with non entangled pairs. This is a pretty tall order for a hobbyist, but I would think not complex for say a graduate level lab. This must have been done.

    Any thoughts.

  3. #3
    mixedgas's Avatar
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    I had a What the Fudge moment like Planters when I watched this video. Then I remembered a former employer had sent me to a non-linear optics seminar for a week. I was there because we sponsored the seminar, not because I was expected to learn it. I ignored all Type I discussion at the seminar because all I cared about was Type II.
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    She's vastly simplified the explanation, and left a lot out. Sadly she left out a few critical things.
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    Type Two non-linearity can occur with six possible input photon states. Type One is far more selective, I think its only two or three input states for a 45' input. However the output when doing Type I sub-harmonic generation will decompose into the two output polarizations with a 50/50 probability, if the sub-harmonic phase matching input characteristics are met.
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    The few incoming photons that meet the right conditions for type I non-linearity in a parametric oscillator are down converted, and exit at a specific walk-off angle. If she has an entangled pair, thus they co-incide on the detectors on the angled path. If she has a non-selected input photon, the Type One crystal does nothing, acts as a waveplate, and the photons are de-selected for detection and pass straight thru.
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    Un-entangled, unconverted photons exit with one rotated polarization, and on axis with the input beam. Entangled photons exit at a specific angle and a 50/50 chance of either orthogonal polarization. They will co-incide on the two detectors at the same time, allowing for corellation detection.
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    Two NLO crystals suggest there SHOULD be at least four possible selection exit paths for entangled photons. She's missing something in her talk.
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    I barely understand this property for Type One, take my explanation with a grain of salt. I just use non-linear crystals for fun and profit. I hate the theory part.
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    They paid a lot of money for a crystal house to pre-align this crystal pair for them. I'm guessing X-Ray orientation was used.
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    Lets paint this for what it is. Scientist Dad is working very hard to place his Daughter on a specific, advanced, scientific career path. Good Quantum Mechanics people need about a half decade of study before they can clearly explain what they are working towards. She's not there yet.
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    Steve
    Last edited by mixedgas; 12-05-2015 at 11:54.
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  4. #4
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    Thanks Steve. I agree with both your conclusions. Now let's get to work. This really interests me if it can actually be demonstrated that entangled photons interact "instantaneously". I'm not naive to the lure of the alchemists claim of lead to gold, cold fusion and faster than light. But, this is a matter of seeing from ever higher and higher points of view. Newton was right, but Einstein showed that he was right within limited conditions. Einstein was right (I'm sure), but probably, also within limited conditions, ie string theory. I know that many labs are studying entangled photons, you read about it all over the place. But, straight forward, reproducible demonstrations of instantaneous interactions? I'm not finding them. It would seem you would face the problem of identifying specific pairs while at the same time producing sufficient flux to overcome shot noise.

    I want to do this and modulate the Pockels cell with an audio signal to be able to actually say, "Mr. Watson, come here" and get him here just a little quicker.

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