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Scientists teleport two different objects
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#12
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Scientists teleport two different objects
: Alan Anderson
: An object (particle, photon, whatever) disappears from one location. Nope. It stays right where it was. It's quantum state is rooned, that's all. : An absolutely identical object (particle, photon, whatever) appears at : another location. Nope. It stays right where it was also; it just aquires the state that the first got rooned. I does not call that teleportation, nor have any truck with them as does. Well, other than to respectfully (or sometimes not so respectfully; I am only mortal) disagree with them. See for example http://www.its.caltech.edu/~qoptics/teleport.html which says (among other things) In quantum teleportation, an unknown quantum state is faithfully transferred from a sender (Alice) to a receiver (Bob). To perform the teleportation, Alice and Bob must have a classical communication channel and must also share quantum entanglement -- in the protocol we employ*, each possesses one half of a two-particle entangled state. Alice makes an appropriate projective measurement (Bell measurement) of the unknown state together with her component of the shared entangled state. The result of this measurement is a random piece of classical information which Alice sends to Bob over their classical communication channel. Bob uses this information to choose a unitary transformation which he performs on his component of the shared entangled state, thus transforming it into an output state identical to the original (unknown) input. Note particularly the bits about the classical communication channel involved in the process. Wayne Throop http://sheol.org/throopw |
#14
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Scientists teleport two different objects
: Alan Anderson
: I choose to indulge in the semantic shortcut of considering the act of : moving the quantum state from one object to another to be just as good : as moving the object which has that state. I further choose to believe : that we can disagree on this topic without either of us being : objectively wrong. Well OK, but note that the only novel thing is the xfer of *quantum* state; classical or nigh-classical states could be moved in that way (ie, an atom emits a photon, another one somewhere else absorbs it and gets the "same" excited state the original had), but nobody says they "teleported" the atom. I don't quite see why quantum-ness deserves the upgrade in terminology. Wayne Throop http://sheol.org/throopw |
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Scientists teleport two different objects
Wayne Throop wrote: : Alan Anderson : I choose to indulge in the semantic shortcut of considering the act of : moving the quantum state from one object to another to be just as good : as moving the object which has that state. I further choose to believe : that we can disagree on this topic without either of us being : objectively wrong. Well OK, but note that the only novel thing is the xfer of *quantum* state; classical or nigh-classical states could be moved in that way (ie, an atom emits a photon, another one somewhere else absorbs it and gets the "same" excited state the original had), but nobody says they "teleported" the atom. I don't quite see why quantum-ness deserves the upgrade in terminology. Assuming that tech wasn't a major issue and extremely high (but finite) effort can be applied to the task, does this actually allow a perfect copy ? My (limited) understanding of the process is that it is a method to just bypass Heisenberg. However, the copy is not perfect as it is a digital process. In effect, what it allows is that the position and velocity of every particle in a person's body to be "measured" to any finite accuracy (though the measurement doesn't actually require observing the particle directly). This position and velocity can then be applied to the target atomic particles. Presumably, the amount of classical bits transmitted and entangled bits required are equal. Also, the number of bits is equal to the "measurement" resolution. In principle, the process could be applied directly to quarks rather than dealing with protons and neutrons. In fact, the lower down the particle scale, the more accurate the reproduction. OTOH, it is likely that a person's personhood is based purely on the configuration of atoms in the brain and EM fields (maybe). Maybe there is a need to also copy any photons floating around in the brain . In fact, it is not really the atoms, people have no problem with the fact that the atoms that make up their bodies are constantly changing. It is the patten that counts. |
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Scientists teleport two different objects
:
: Assuming that tech wasn't a major issue and extremely high (but finite) : effort can be applied to the task, does this actually allow a perfect : copy ? I don't think so; I don't see how it would. A very specific quantum state is transfered; lots of other things aren't transfered. The particle doesn't really "look the same" classically at all, naict. So depends on what you're attempting to copy; it doesn't seem applicable to copying, say, apples or bicycles. Wayne Throop http://sheol.org/throopw |
#17
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Scientists teleport two different objects
Wayne Throop wrote: : : Assuming that tech wasn't a major issue and extremely high (but finite) : effort can be applied to the task, does this actually allow a perfect : copy ? I don't think so; I don't see how it would. A very specific quantum state is transfered; lots of other things aren't transfered. The particle doesn't really "look the same" classically at all, naict. So depends on what you're attempting to copy; it doesn't seem applicable to copying, say, apples or bicycles. Can it not be used to copy the position of an atom ? For example, if I have 3 entangled photons, can I copy the position of an atom to 3 bits of resolution ? Step one: confirm the source atom is in a volume much larger than Heisenberg's limit. Step two: Do some fancy measurements in conjunction with the photons. The measurements would be a binary search or something. Step three: Use the other half of the photons + results of measurement to position the other atom. This then copies the atom's position ... but only to 3 bits of accuracy. |
#18
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Scientists teleport two different objects
" wrote:
Can it not be used to copy the position of an atom ? For example, if I have 3 entangled photons, can I copy the position of an atom to 3 bits of resolution ? Step one: confirm the source atom is in a volume much larger than Heisenberg's limit. Step two: Do some fancy measurements in conjunction with the photons. The measurements would be a binary search or something. Step three: Use the other half of the photons + results of measurement to position the other atom. This then copies the atom's position ... but only to 3 bits of accuracy. I can't tell what you're asking. Your words do not match anything I know of regarding quantum teleportation. What quantum teleportation does is to transfer the quantum state of a target object to to a destination object with perfect fidelity. That would be something like its polarization or its spin. It has to lose the original state in the process, so it isn't able to "copy" anything. (Position can already be measured to an arbitrary precision using classical methods, though you lose information on momentum as you gain it in position and vice versa.) |
#19
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Scientists teleport two different objects
RobH wrote: Scientists teleport two different objects POSTED: 4:36 p.m. EDT, October 4, 2006 [fun with quantum entanglement] Am I correct in thinking that this technology is FTL, and not subject to any kind of range restriction or interference/ signal blockage? Can we therefore imagine that some future interplanetary mission might take with it a lump of entangled particles (having left the entangled 'mates' of those particles back on Earth), allowing the spacecraft and mission control to exchange data instantaneously, no matter how far away the craft travels? What would the bandwidth be like? Presumably it would be 1 bit per entangled particle pair, but is there any restriction on the rate at which these bits can be sent other than the speed at which the the computers involved can 'read' and 'write' the particles? However, I suppose there would be a finite amount of data that could be transmitted in this way, defined by the amount of entagled particles available to the ship. What would we call that, 'banddepth'? Given that these particles are at an atomic scale though, I imagine a just a few grams of material would be enough for many billions of bits of data. The advantages of eliminating comm-lag for manned space travel are obvious, but I could see that even on unmanned missions this would do away with a lot of hassles associated with traditional radio transmissions. Or have I misunderstood completely? The only future applications the articles I've read seem to be interested in are secure data communication (very exciting for gov, mil and biz I'm sure but... well.... *yawn* ) and "beam me up scotty" style teleportation (which, let's face it, ain't gonna happen). I find it hard to believe that such a potentially revolutionary technology (a) really is as useful as I understand it to be and (b) isn't generating more of a buzz. Someone please correct my misconceptions (if I have expressed any). |
#20
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Scientists teleport two different objects
:
: Am I correct in thinking that this technology is FTL, and not subject : to any kind of range restriction or interference/ signal blockage? : : Can we therefore imagine that some future interplanetary mission might : take with it a lump of entangled particles (having left the entangled : 'mates' of those particles back on Earth), allowing the spacecraft and : mission control to exchange data instantaneously, no matter how far : away the craft travels? No. Or rather, you can imagine it (and, eg, Stross did in Singluarity Sky and Iron Sunrise), but there's not much of a justification for it in the theory and practice of quantum so-called-teleportation. Because, in order to accomplish the so-called-teleportation, you must 1) make a measurement at the souce, 2) send a message about what you found to to the destination, and finally you can 3) cause the "quantum state" to "teleport". Note specifically step 2. Wayne Throop http://sheol.org/throopw |
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