Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Momentum Entanglement

  1. Mar 9, 2017 #1
    I rarely hear about momentum entanglement, do you know any experiments/applications for momentum entanglement?

    If we do momentum entanglement on 2 particles, and then we accelerate one of the particles, will the other particle slow down to obey conservation of momentum? or entanglement will be destroyed?
     
  2. jcsd
  3. Mar 9, 2017 #2

    Nugatory

    User Avatar

    Staff: Mentor

    No. Whatever interaction is involved in accelerating the particle will also break the entanglement.
     
  4. Mar 9, 2017 #3
    What about gravitational acceleration? it will not involve direct interaction with the particle.
     
    Last edited: Mar 9, 2017
  5. Mar 9, 2017 #4

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    A very minor quibble, O Nugatory One, and I am probably going to put my foot in my mouth before finishing... :smile:

    If that interaction has the effect of being an irreversible measurement, then of course you are correct. However, there are transforms that don't have that effect. And those do not break entanglement.

    Frequency entangled photons (essentially momentum entangled) can move through fiber, changing their direction. They can even have their frequency modified (boosted for example) without breaking their entanglement. As long as no information is gained about their momentum.

    I assume similar transforms could occur with electrons.
     
  6. Mar 9, 2017 #5

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    This is an open question. Quantum gravity would imply that there might be an effect (however small). Otherwise, it should not.
     
  7. Mar 9, 2017 #6

    Nugatory

    User Avatar

    Staff: Mentor

    Indeed there are.... But I am having trouble imagining one that would could be said to "accelerate the particle" in the sense that the OP is thinking about (that is, we know that the result of a momentum measurement after the interaction will be different than before) without breaking the entanglement. That may be a failure of imagination on my part.

    In any case OP's line of thought, that we can "slow down" the other particle seems completely illegitimate. "Slow down" implies that the other particle had some (counterfactual) velocity that we've reduced by our interaction with the first particle.
     
  8. Mar 9, 2017 #7

    Strilanc

    User Avatar
    Science Advisor

    You should be able to boost the momentum of a particle without breaking entanglement. We can precess spins with a magnetic field without breaking their entanglement and it's basically the same idea I think.

    It's actually an interesting exercise to figure out why the boosting/precessing doesn't necessarily measure the momentum or spin, despite momentum conservation / angular momentum conservation requiring that some external system be pushed in the opposite direction.
     
  9. Mar 9, 2017 #8
  10. Mar 10, 2017 #9
    So lets say we used 2 electrons, and the speed of the 2nd electron was boosted without breaking the entanglement (which as I understood from the comments is possible), what will happen to the 1st electron? will it slow down?
     
  11. Mar 10, 2017 #10

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Definitely not. Under no scenario that has been discussed above - which is the exception and not the rule - will doing something to A's momentum cause a related change in B's momentum. The question above is only whether there can be alterations to A's momentum that do NOT break the momentum entanglement with B.
     
  12. Mar 10, 2017 #11
    But my question was about momentum entanglement
     
  13. Mar 10, 2017 #12

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    And the answer is: accelerating A does not decelerate B in any related manner. It would normally break the entanglement with B (as Nugatory said), but there are occasions which it might not. Gravity would not break entanglement, unless it is a quantum force.
     
  14. Mar 10, 2017 #13
    What about conservation of momentum why it will not hold (in case entanglement was not broken)?
     
  15. Mar 10, 2017 #14

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    There is conservation of momentum. Entangled A+B is a constant prior to any acceleration X acting on A. After including X, you have (A+X) +B. Conservation holds.
     
  16. Mar 10, 2017 #15
    Ok. So what you are saying in other words is that any added momentum for one of the particles will add to the total momentum of the entanglement system and momentum will be conserved with this new value.

    So if we have pA+pB= p and we added x momentum to A then that is equivelent to saying pA+pB = p+x

    Its interesting that we can manipulate the total entanglement state without breaking the entanglement.
     
  17. Mar 10, 2017 #16

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Yes, and again there are caveats around that. I don't know of any good experimental references for that for particles with mass - only for light. But I believe the theory is the same.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted