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Quantum entangled particles

  1. May 6, 2009 #1
    I am a Combat Medic in the US Army and have a few questions to ask. I am not a physicist nor would I pretend to be. I am just a curious mind. I am very new to this so these questions may be very simple.

    1. Is it possible to capture an entangled particle?

    2. If so can these particles be separated? Perhaps two electrons orbiting two separate atoms?

    3. Can the captured particle be monitored?

    4. Is it possible to manipulate the particles?

    5. If so can it be done in a predictable/detectable manner? Exp: Slow down or speed up. Perhaps even change direction.
     
  2. jcsd
  3. May 6, 2009 #2
    There is nothing special about entangled particles, other than that the state of one of them depends on the state of the other. Even if they are separated by a large distance (as large as you want), when you measure the state of your particle, you know instantly what the state of the other particle will be, if it was measured.

    They are not entangled in the sense that they are somehow stuck together or something.
     
  4. May 6, 2009 #3

    DrChinese

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    Welcome to PhysicsForums, Belzy!

    The answer is YES, you can capture and manipulate entangled particles. There are many novel experiments being performed daily on entangled particles. One of the most common is to take a laser and shine it into a PDC crystal. This causes 2 beams of light to emerge at very specific off angles. The light particles in each beam are entangled. They can then be manipulated and tested in a variety of ways.
     
  5. May 6, 2009 #4
    Thank you for taking the time to read my post.

    Lets say you have two known quantum entangled particals and you separate them by a given distance. Maybe one in New York and one in Paris. Both being monitored constantly, but only one is being manipulated in a known pattern to signify the postion of either on or off. Would this not be a way to communicate digitaly faster than light?
     
  6. May 7, 2009 #5
    The problem is the monitoring... Entanglement endures while you don't measure. As soon as you measure, entanglement is gone. That's why you can't use it for superluminal speed.

    The only thing you will get (check out the EPR "paradox" in wikipedia, e.g.) is a correlation between measurements of the two particles (one in NY, other in Paris) which can't be explained within classical mechanics.

    On the other hand, entanglement is not useless... it is a resource that can be used, e.g. in quantum computation, quantum cryptography, etc.
     
  7. May 7, 2009 #6

    DrChinese

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    You can manipulate entangled particles, but you cannot prepare them in the manner necessary to perform FTL signalling. You can probably imagine that this issue has been considered in depth. :)

    If fact, there are no-go papers on using entanglement to send signals >c. But the main point is this: you cannot force a single specific entangled particle into a specific state. You can perform what is called "post-selection", in which you only consider particles that have the attributes you desire. But consider our 2 observers, Alice and Bob. Alice waits for a particle with an "up" orientation, which occurs 50% of the time. How is Bob supposed to know those particles' twin partners from the other 50%?

    In other words, a beam of entangled particle pairs is randomly oriented for all entangled attributes. So there isn't a way to use those random orientations to send a signal. Work through an example, and you will see there isn't enough to work with to get the desired result.
     
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