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Thread: Suspending electrons in light

  1. #1 Suspending electrons in light 
    Forum Freshman WilJake's Avatar
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    So I was reading an article and I had a thought, pharmacists are using sound to suspend particles to study them in a fluid state, what if someone would try to suspend electrons in light? The electron would have nowhere to go, so where would the energy go? Would it be possible? If so wouldn't it conflict with the Heisenberg Principle? What are your thoughts?


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    Forum Freshman WilJake's Avatar
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    If anybody was curious, here is the article I was looking over (I had known of this for a while, but was emailed the article by a friend yesterday)
    Video: Government Wizards Levitate Drugs With Ultrasonic Sound | Popular Science


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    Forum Ph.D. merumario's Avatar
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    it won't be possible,even if it is,what am i saying,it cannot be....what would you use in doing this? and am not sure light consist of electrons but photons.
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    Forum Freshman WilJake's Avatar
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    You would have photons coming from different sides, look at the link I posted, and imagine photons instead of sound, and instead of the fluids it would be electrons.
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    Quote Originally Posted by WilJake View Post
    You would have photons coming from different sides, look at the link I posted, and imagine photons instead of sound, and instead of the fluids it would be electrons.
    See Compton Effect. Photons and electrons interact.
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    Brassica oleracea Strange's Avatar
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    There are things like optical tweezers and laser traps which use light to manipulate objects. Whether it works with individual electrons, I'm not sure...
    ei incumbit probatio qui dicit, non qui negat
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    Forum Freshman WilJake's Avatar
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    The biggest challenge would be isolating a single electron, but I think that science isn't to far away. After that I'd love to see how the electron acted. In theory, wouldn't it reach absolute zero? There would be no molecular motion?
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    First of all, your question isn't correct. The energy doesn't 'go' anywhere. The only energy a free electron has (not regarding relativistic energies) is its kinetic energy. Trapping it (we usually use ion pits/wells for that) will however make it quantized. And though we have already fine this, it is impossible to observe a free electron isolated, because well, you isolate it. And it becomes quantized.Doing this with light is possible i think, but not very easy. Since one would need to couple to spins which very weak.
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    Forum Freshman WilJake's Avatar
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    Quote Originally Posted by Kerling View Post
    First of all, your question isn't correct. The energy doesn't 'go' anywhere. The only energy a free electron has (not regarding relativistic energies) is its kinetic energy. Trapping it (we usually use ion pits/wells for that) will however make it quantized. And though we have already fine this, it is impossible to observe a free electron isolated, because well, you isolate it. And it becomes quantized. Doing this with light is possible i think, but not very easy. Since one would need to couple to spins which very weak.
    Thanks for clearing that up, but the thought would still be possible, correct? I think it would make an interesting experiment. But my other question still applies, wouldn't this go against the Heisenberg Principle? You'd trap the electron n a single place, while observing it.
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    Forum Professor arKane's Avatar
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    Quote Originally Posted by WilJake View Post
    Quote Originally Posted by Kerling View Post
    First of all, your question isn't correct. The energy doesn't 'go' anywhere. The only energy a free electron has (not regarding relativistic energies) is its kinetic energy. Trapping it (we usually use ion pits/wells for that) will however make it quantized. And though we have already fine this, it is impossible to observe a free electron isolated, because well, you isolate it. And it becomes quantized. Doing this with light is possible i think, but not very easy. Since one would need to couple to spins which very weak.
    Thanks for clearing that up, but the thought would still be possible, correct? I think it would make an interesting experiment. But my other question still applies, wouldn't this go against the Heisenberg Principle? You'd trap the electron n a single place, while observing it.
    You talk about observing an electron as if that's easy to do. Can you describe the instruments that can do that please?
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    Forum Freshman WilJake's Avatar
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    Quote Originally Posted by arKane View Post
    Quote Originally Posted by WilJake View Post
    Quote Originally Posted by Kerling View Post
    First of all, your question isn't correct. The energy doesn't 'go' anywhere. The only energy a free electron has (not regarding relativistic energies) is its kinetic energy. Trapping it (we usually use ion pits/wells for that) will however make it quantized. And though we have already fine this, it is impossible to observe a free electron isolated, because well, you isolate it. And it becomes quantized. Doing this with light is possible i think, but not very easy. Since one would need to couple to spins which very weak.
    Thanks for clearing that up, but the thought would still be possible, correct? I think it would make an interesting experiment. But my other question still applies, wouldn't this go against the Heisenberg Principle? You'd trap the electron n a single place, while observing it.
    You talk about observing an electron as if that's easy to do. Can you describe the instruments that can do that please?
    I'm not saying this is possible with modern technology, hence the reason 've used the phrase "In theory" so many times.
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    I appreciate the message in your sig line... But could you please tone it down to a smaller and less in your face font and color?
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    Forum Professor arKane's Avatar
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    Quote Originally Posted by WilJake View Post
    I'm not saying this is possible with modern technology, hence the reason 've used the phrase "In theory" so many times.
    Okay, welcome to the forum.
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    Forum Ph.D. merumario's Avatar
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    so it is still fiction....please fix your eyes.
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    Quote Originally Posted by WilJake View Post
    Thanks for clearing that up, but the thought would still be possible, correct? I think it would make an interesting experiment. But my other question still applies, wouldn't this go against the Heisenberg Principle? You'd trap the electron n a single place, while observing it.
    Well, I must warn you that I am a theorist so that the practical application of my thoughts are generally about 10 times harder then I imagine.
    The thing is that Electrons are free particles, which means that they are isotropic. Also they are free, so in contrast to bound electrons their energy spectrum is continues. The problem is, the heisenberg principle. Because one doesn't exactly know both the momentum and position, it is very hard to determine how to 'trap it' (creating optical walls to capture it in place)
    If we'd assume it is squeezed, and has therefore reached the heisenberg limit. Even still we'd just have a certain spread of position. And a spread in momentum. The problem is, that once we do this propperly, the Electron is no longer free, but point and will stop having a continues energy spectrum and become discrete. Just like in an atom.
    Then it will gain an electric dipole moment, and it will either absorb or emit light itself. Making the trap useless.
    The thing is, that this happens with all particles, however the lighter they are the quicker this happens (quick as in from large to small traps).
    Basically it is impossible to trap the electron determistally. As if we'd know its self interference, we'd be clueless about its momentum, and hence energy. :P
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    Forum Ph.D. merumario's Avatar
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    and i believe the above means we cannot voilate uncertainty and still have the electron as an isotropic particle....if it ever can be done then the electron will change some of its features making it less an electron...unless i am missing something.
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    Quote Originally Posted by merumario View Post
    and i believe the above means we cannot voilate uncertainty and still have the electron as an isotropic particle....if it ever can be done then the electron will change some of its features making it less an electron...unless i am missing something.
    You've mixed up several concepts in your post, and confused yourself by assuming things that aren't quite true.

    The HUP tells us that, even at zero kelvins, there must still be motion (otherwise we'd know both position and momentum, say). That "zero point" motion is well understood, but has nothing whatever to do with the question of trapping an electron.

    Light (more specifically, a laser) is a lousy tool for trapping a charged particle because of the large forces involved. It takes very little to move the electron out of the field of the laser, at which point you've lost it. Lasers (optical tweezers) work great on neutral particles, where this problem does not appear.

    For charged species, the trap of choice is the Penning trap. CERN uses them as antiproton warehouses; physicists probing matter near absolute zero have trapped single electrons for many months at a time. By "trap" is not meant "stop all motion," so the HUP doesn't enter into the question in any direct way. You should interpret "trap" as meaning "confine to a small volume." There is certainly motion within that trapping volume (indeed, we probe the trapped charge by observing its resonance with an applied microwave field; and we cool it further by letting it radiate microwave energy).

    So, we can "suspend" electrons, but using light to do it is fraught with such practical difficulty that we use the properly shaped macroscopic E- and H-fields of a Penning trap to do it instead. Cooling electrons down to tens of millikelvins is routinely achieved with such apparatus.
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  19. #18  
    Forum Freshman WilJake's Avatar
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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by merumario View Post
    and i believe the above means we cannot voilate uncertainty and still have the electron as an isotropic particle....if it ever can be done then the electron will change some of its features making it less an electron...unless i am missing something.
    You've mixed up several concepts in your post, and confused yourself by assuming things that aren't quite true.

    The HUP tells us that, even at zero kelvins, there must still be motion (otherwise we'd know both position and momentum, say). That "zero point" motion is well understood, but has nothing whatever to do with the question of trapping an electron.

    Light (more specifically, a laser) is a lousy tool for trapping a charged particle because of the large forces involved. It takes very little to move the electron out of the field of the laser, at which point you've lost it. Lasers (optical tweezers) work great on neutral particles, where this problem does not appear.

    For charged species, the trap of choice is the Penning trap. CERN uses them as antiproton warehouses; physicists probing matter near absolute zero have trapped single electrons for many months at a time. By "trap" is not meant "stop all motion," so the HUP doesn't enter into the question in any direct way. You should interpret "trap" as meaning "confine to a small volume." There is certainly motion within that trapping volume (indeed, we probe the trapped charge by observing its resonance with an applied microwave field; and we cool it further by letting it radiate microwave energy).

    So, we can "suspend" electrons, but using light to do it is fraught with such practical difficulty that we use the properly shaped macroscopic E- and H-fields of a Penning trap to do it instead. Cooling electrons down to tens of millikelvins is routinely achieved with such apparatus.
    So, what you are saying is something along the lines that although it is possible in theory, it would just be so difficult, that using alternative methods to "freeze" the electron would be much easier, and more practical, right?
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    Quote Originally Posted by WilJake View Post
    So, what you are saying is something along the lines that although it is possible in theory, it would just be so difficult, that using alternative methods to "freeze" the electron would be much easier, and more practical, right?
    Thanks for the succinct English-to-English translation!

    The very large sensitivity to electric fields that makes trapping an electron with light so difficult happens also to make trapping with E- and H-fields the natural choice.
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    And a special thanks from me is next to be said,
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  22. #21  
    Forum Ph.D. merumario's Avatar
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    thanks tk421....nice view of the thread.
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