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Underground > Laboratory >

Teleportation is achieved....with lasers

00:53 / 18.06.02

check this out. I think other scientists have done similar successful experiments with teleporting beams of light before.......

http://www.cnn.com/2002/TECH/science/06/17/australia.teleporting.reut/index.html

Basically they were able to teleport (break down and then reassemable in a different place) a laser beam. They say in theory, it should work for physical and maybe someday even organic objects, but that those things are a long way off. But what's interesting is they keep repeating that in theory, it should work.

08:38 / 18.06.02

I wouldn't get too excited. Quantum teleportation, as far as I know, is something that is used to be able to extract all of the physical information about a body, rather than the limited subset that can be obtained through conventional means (due to the uncertainty principle). But you still have to use that information to rebuild the original item. I guess it's relatively easy to create a laser beam, but recreating anything more complex would be ridiculously difficult.

All this stuff about "it could happen" is PR - it's been known to be theoretically possible since the theory was developed some years ago. I'd ignore it.

The major use for this is in quantum computing, and that's the important bit right now. I'm not by any means an expert on quantum computing either so I couldn't tell you exactly where in the process it would be useful... but apparently it's one of the major aspects.

12:44 / 18.06.02

I have to agree with fridgemagnet that making teleporation happen from objects that aren't "quantum" (eg photons) will be pretty hard. IIRC, Star Trek gave a nod to the scientific community by including a "Heisenberg Compensator" in their teleporter. So apart from the sad Trekkie reference, there is a serious point here. If you want to teleport an object atom by atom, how do you make sure that the atoms end up in the same relative position and moving at the same relative velocities? Heisenberg says that the more accurate you are with one, the less accurate you are with the other. Perhaps a little wobble and rearrangement won't hurt.....

As for quantum computing, I think the idea is that by using quantum entanglement and teleportation you can transmit data faster than light. The explanation of how you can do that in a relativistic universe is probably a bit tricky...

13:18 / 18.06.02

From what I was reading, it seems that the quantum teleportation thing is using quantum entanglement somehow to get information on the spin etc of the original's atoms - something like, you interact one lot of entangled stuff with the original, then use the other lot to form the copy - but it requires the destruction of the original, so on that basis it doesn't break the uncertainty principle.

(Wasn't I saying last night that "quantum" was a dirty word, often used badly? I think I'm proving that here.)

13:40 / 18.06.02

I was thinking that the uncertainty principle might be violated in the reassembly of lots of atoms. So, you teleport the first one and it ends up somewhere. The next (original) atom had a relative position and velocity to the first and so should be teleported to the same position and velocity relative to the copy. OK, so they don't happen one at a time but with a touch of sophistication I can imagine making this argument work.

Perhaps I'm wrong, but doesn't the uncertainty principle say that there is a bound on how accurately you do this? And it becomes worse the more fundamental particles are involved?

Dunno. Its a minefield where its so easy to get the wrong end of the stick.

15:55 / 18.06.02

as I understand it they're not really teleporting things, they're constructing perfect models of them and then rebuilding those. The article keeps comparing the process to using a fax...

---
In conventional facsimile transmission the original is scanned, extracting partial information about it, but remains more or less intact after the scanning process. The scanned information is sent to the receiving station, where it is imprinted on some raw material (eg paper) to produce an approximate copy of the original.

In quantum teleportation two objects B and C (which are entangled) are first brought into contact and then separated. Object B is taken to the sending station, while object C is taken to the receiving station. At the sending station object B is scanned together with the original object A which one wishes to teleport, yielding some information and totally disrupting the state of A and B. The scanned information is sent to the receiving station, where it is used to select one of several treatments to be applied to object C, thereby putting C into an exact replica of the former state of A.
---

16:17 / 18.06.02

True, but then a fax isalso susceptible to my argument. In order to assemble the fax, one has to put the first line just above the second line and be sure that the first line, or the paper it is written on, doesn't have a large velocity with respect to doodah that writes the second line. More technically, if you use the first line you write as a point of reference, then you need to be approximately certain of the relative velocites and positions of the other lines as you write them. For a fax the errors are insignificant.

Now, Quantum teleportation is, as you say, like a fax. But since it relies on quantum effects, you have to "transmit" atom by atom probably. This means that in the reassembly you need to get a pretty good picture of how to put everything back together again. I need to think harder about whether this really is a problem - is the effect cumulative or do you just get an independent uncertainty for each building block?

19:41 / 18.06.02

AFAIK the quantum bit is really just to do with the information gathering and transfer - the actual atoms that are involved don't move. You have your lump of entangled matter, which you then separate into two bits, one for the start (B) and one for the destination (C). Then, you use the bit at the start to analyse your object (A), which in the process destroys it, but which preserves all of the details that you normally can't observe. I suppose that since they're not actually being observed until you rebuild at the other end, you don't have to worry about them until that point, so you can have an absolutely perfect scan, and transmit the information instantaneously to the matter at C.

But the actual scanning process - I don't have a scooby how that works, whether it does everything at once, whether it does it atom-by-atom... I guess that to preserve the structure you'd have to do it all simultaneously, but from that paper I can't say how that would work.

20:14 / 18.06.02

Hmmm. My understanding was that entanglement only really happens at the quantum level - though I think they are trying to push the limit of this as to include molecules. If that is the case then if you want to "teleport" something big, you have to entangle it molecule by molecule and you definitely need some reassembly process.

All of which makes it sound as if the process is completely unfeasible. The solution is to try to entangle the object you are trying to "transmit" as a whole. I have no idea if that is possible for large objects but I imagine that in order to make sense of that for objects with a lot of structure, you need to have something close to a replica to start with...