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Quantum teleportation of macroscopic objects

  1. Aug 4, 2011 #1
    I've started a couple of threads about this topic before, but those were a while ago, and I still have some nagging questions.

    1.) If we wanted to quantum teleport something macroscopic, would scanning come into play? I thought that the whole point of QT was that you don't have to scan whatever it is you want to teleport. Would the only scanning take place before QT, in order to figure out the configurations and positions of the atoms so that a replica could be made at the destination (let's say the destination has stores of materials that they could use to make identical replicas)? Once the two objects are entangled, don't we just have to measure the quantum state of the object at the source and then send the result of the measurement to the destination? Wouldn't the entire object have one quantum state, as opposed to each atom having a state that must be measured?

    2.) I understand that, in all of the experiments done so far in QT, the atoms were at close to absolute zero. For macroscopic objects to be quantum teleported, how low would the temperature have to be? Would you risk converting the object to a Bose-Einstein condensate, or in any other way fundamentally and irreversibly altering the object, by lowering it to a temperature suitable for QT?

    3.) I once suggested that, if scanning was necessary, we could use nanobots that would infiltrate the object (if it was a human, they would go through the bloodstream and blood vessels), but was told that the energy required to scan all the atoms in such a short time frame would create a black hole. How so?

    4.) This is kind of related to another thread I recently started, but if we wanted to entangle the two objects, would we have to entangle them atom-by-atom, or could we entangle the entire object? Would we have to keep the two objects close to each other and then send them apart?
     
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  3. Aug 5, 2011 #2

    Chronos

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    You would need to 'force' every atom of the macroscopic object into the same quantum state simultaneously. That would be difficult.
     
  4. Aug 5, 2011 #3

    DrChinese

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    Scanning? Teleportation? Nanobots? This is sorta going Star Trek here. Most of this makes little scientific sense. Can you bring it back to a specific question about something which is not born from fiction? Thanks.
     
  5. Aug 5, 2011 #4

    Ryan_m_b

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    *Sigh, as someone in the field of medical nanotechnology it https://www.physicsforums.com/blog.php?b=3179" [Broken] their paper.
     
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  6. Aug 5, 2011 #5

    xts

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    Welcome to the club! I am a bit farther from nano-tech, but I believe I got some insider's view on quantum engineering, and I may to say the same about all that hi-pitch excitation about teleportation, time-travelling, etc... Like this thread ;)

    [ No, Hammertime! It is impossible to teleport macroscopic objects. It is impossible to teleport even single atom. What you may teleport is some quantum property of an object. And you may teleport only discrete properties - like spin, or excitation state of ion - but you can't teleport even simplest continuous property (like momentum). So forget about teleporting humans! Especially deep-frozen humans. ]

    People really don't understand Anton Zeilinger's Schlagwort: Papers must be sexy.
    Many of them think that covering their boring ideas with shining red lipstick of words like 'nano-' 'teleportation', and 'quantum' makes them sexy...

    Calgonit Quantum - the unbeatable dishwasher tabs - http://www.finish.de/index.php
     
    Last edited: Aug 5, 2011
  7. Aug 5, 2011 #6

    Ryan_m_b

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    Grrr products like that grind my gears! I really like this article published in Nature by Andrew Moore. It's a little old now but the point still stands; with so many different research groups, science/engineering disciplines, pop-sci/sci-fi authors, NGOs, government departments and companies using the term "nanotechnology" there's a real danger that it's meaning will be completely lost on the public and it will become a useless word. I especially like this section...
    EDIT: I realise this may seem to be getting a bit off-topic so to make it more relevant:
    hammertime I'd advise you to take a look at the topics discussed here in depth so that you can look towards getting a proper understanding of the sciences involved rather than a confused pop-sci and sci-fi understanding.
     
    Last edited: Aug 5, 2011
  8. Aug 5, 2011 #7
    There is no need to scan the hole object. That is the point of quantum teleportation, you send your unknown quantum state to another person and the person is sure that is your state (with high fidelity).

    However, you and your partner need to share a quantum channel - i.e, a quantum entangled state. In theory, if you can produce a macroscopic entangled state (called two-mode Schrodinger-cat states), you could teleport a macroscopic object. There are some experiments on this. Btw, it is possible to teleport an atom.

    The problem with big objects for me would be in the measurement that you do. You have always to perform a joint measurement in the state you want to send and in the state of the channel, and this should be not very trivial for big objects - even in the simplest cases of quantum objects this is hard. Also, maybe the amount of classical information would scale brutally.
     
  9. Aug 5, 2011 #8

    DrChinese

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    Welcome to PhysicsForums, MrDementao!

    You left off the words "state of" here, i.e. you can teleport a state rather than the actual atom. And I am a bit dubious about teleporting "the state" of an entire atom. Do you have any references so I can see what you are referring to specifically?
     
  10. Aug 5, 2011 #9

    xts

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    Any references? On teleportation of the object, not just it single (or few) discrete properties?
    The whole state of atom had been teleported? Or its spin or excitation only?
    In case of continuous property (like position or momentum) - it would require infinite amount of information. Well, you may probably cut it off at Planck's scale. Then finite (but large) amount of information is sufficient...
     
  11. Aug 5, 2011 #10
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  12. Aug 5, 2011 #11

    xts

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    What about other properies? Spins? Atom momentum/position? Nucleus state?
    We have just few discrete parameters, not the whole atom.

     
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  13. Aug 5, 2011 #12

    DrChinese

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    This reference isn't really much (didn't even mention the paper's authors). Here is an "associated" reference from the same group of scientists a few years later:

    http://arxiv.org/abs/0704.2027

    I just want to caution readers about the use of the word "teleport". In general, using entanglement, a quantum state is moved from particle A to particle B. No actual force or matter is moved anywhere as a result of the process.
     
  14. Aug 5, 2011 #13
    The properties are the same, since is the same quantum state. They teleported the state of the atom. There is not a difference between atom and quantum state of the atom. The state - wave function/density matrix - has all physical properties of the atom encoded. In this sense they indeed teleported the whole atom.

    Maybe a better reference:
    http://www.physics.utoronto.ca/~dfvj/Publications%20by%20Daniel%20F%20V%20James/3-Unrefereed_Publications/proc11_ICAPTeleportation.pdf [Broken]

    There are not so much actual experiments, but a lot of proposed schemes. I dont think this will be impossible. It is hard, but not impossible.
     
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  15. Aug 5, 2011 #14

    DrChinese

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    I think it would be safe to say that there is a difference between the two, and certainly a difference in teleporting the two. Some of the issues will end up being semantical though.

    Thanks for the other reference, that helps.
     
  16. Aug 5, 2011 #15

    xts

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    I agree.
    Just one comment. We never use the wave function of the atom. If you solve Schrödinger equation of Tritium atom at the class of QM, you solve the problem of point-like charge (electron) in a field of pointlike charge (nucleus). The wave function you use describe just a small part of atom's behaviour - its energetic states. It says nothing about electron spin.
    You may go further on the way and include spin in more complicated calculations in more dimensional Hilbert space. But your tritium atom suddenly decays. You want cover this too? OK. Let's make all calculations to compute the wavefunction of the nucleus, and quarks within nucleons... All that constitute atom.

    I believe you don't claim any of those experiments entangled not only energetic states of the electrons, but also nuclear ones?

    Another issue is atom position. As long as you teleport single atom, it is preassumed, that new one is in different place than original one and constitutes its own reference frame. But as you want to teleport a system of two or more atoms, you must also reconstruct their relative positions (or rather wavefunction leading to their relative position). And here you fall into a problem of teleporting continuous variable, which require infinite information.
     
  17. Aug 5, 2011 #16
    Yep, we would end going into the definition of what a quantum state is, or what an actual atom is*.

    However, the teleportation scheme in any case is the teleportation of the quantum state, which possess all the relevant physical properties of the atom.

    (* it is hard for me to accept this distinction: What an actual atom has that is not described by its full quantum state?)
     
  18. Aug 5, 2011 #17
    When you teleport the full quantum state it will have all the properties of the original one. And that is the gain in teleportation: you dont need to know which one is your state, you know that after the protocol the state in the other side will be your state. So you dont need to reconstruct your state, or measure its polarization or whatever. You just need to be able to do some Bell-like measurements and comunicate classically.

    There is teleportation in continuous variables with photons. You dont need infinite amount of information to perform it.

    As Dr Chinese said, maybe we have a semantic misunderstanding here.
     
  19. Aug 5, 2011 #18

    xts

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    I don't use this distinction.
    I just say that experiments are done regarding limited-subset-of-full-state, rather than full-state and it seems to be impossible to do any teleportation (or other) experiment operating on the full state.
    Photons have well defined full-state: spin, momentum/position, that's all. For atoms that is not so easy.

    Reference please!

    But I must know what the Hilbert space describing this state is. And teleportation couples only subset of the full-state Hilbert space dimensions.
     
    Last edited: Aug 5, 2011
  20. Aug 5, 2011 #19
    Yes, but consider the following. If we had, say, teleportation stations and at each station there were huge reserves of elements like carbon, hydrogen, oxygen, nitrogen, etc., we could then build a replica of the object whose state we want to teleport at the destination and then QT the state of the object at the source to the object at the destination. Wouldn't that work? That way, we would only need to send information about the position and state of the atoms, as opposed to the actual atoms themselves.

    Yes, I know it's a lot of information to send, but there's no reason we can't send all the information in a certain amount of time. Hell, we could send that information by using a pair of entangled particles! Isn't that the currently expected use of QT? To send information super fast?

    And the part where we determine the position of atoms in the object build the replica at the destination from the reserves of materials? That's where the nanobots come in.
     
  21. Aug 5, 2011 #20
    Huh? Can you elaborate, please?
     
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