# Quantum Teleportation

Hello, this is my very first post on this forum and I think it is very cool. Anyway, I recently learned about how quantum teleportation works, and personally, I think it's the biggest rip off since Miss Cleo. For those of you who do not know how it works, here's how I understand it to work:

Suppose you want to teleport a photon, called Photon A. You would also need two entangled photons, Photons B and C. Whatever happens in one photon happens in the other, even if they are on different ends of the universe. Say that I have photon B and my friend, Cole, who lives miles away has entangled particle C. So I have Photons A and B, and Cole has Photon C. Now I can measure what is going on in Photon A in relation to Photon B. And since Photon B is entangled with Photon C, I know how Photon A is behaving in relation to Photon C. And if I have that information, I can somehow determine the quantum state of Photon A. Cole can then manipulate Photon C to take on the exact quantum state as Photon A. This is how I understand it to work, but if I messed up with anything, please don't hesitate to correct me.

Scientists call this teleportation. I call it an absolute rip off. Just because Photon C is in the exact same quantum state as Photon A does not make it the same photon. Suppose that one day, we can manage to carry this out on larger scales. If I want to "teleport" a package to someone across the world, is it still the same package once it has undergone "teleportation?" Personally, I don't think so. Sure, it's not any different from the package you sent, but it is made up of DIFFERENT particles! Or, venturing into the even scarier, what if we wanted to do this to a person?! Would it still be that person once they have undergone "teleportation"? It looks like the person you "teleported". It acts like the person you "teleported." The particles in the persons body are even in the same quantum state as they were before this bizarre process, but they are not the same particles, therefore it is not the same person. I am very uncomfortable with this method of teleportation.

Let's not forget that there are other ways of teleporting. Wormholes are highly theoretical, nobody even knows if they exist, but evidence has shown that it may be possible to rip the fabric of spacetime and create this link between two locations. You could jump through it and be in the location you wanted to travel to. I am much more comfortable with this because it doesn't involve messing around with the particles in you body.

xantox
Gold Member
Elementary particles are identical, even in principle, so that the very concept of "different" particles of the same species does not exist.

I think fax machine. Or looking at the name of the above poster, xerox photocopy. I have to say though, I'm not impressed with wormholes either.

Thank you for that voltage. I agree with that 100%. It's just like a fax machine or xerox photocopy. Perfect example. However, Xantox said something that I thought was interesting. He said that the very concept of different particles of the same species does not exist because they are all identical. This may be true, but I find it very hard to grasp that concept. Even if they are identical, why on earth would that make them the exact same particles? All I know is that I'm VERY uncomfortable with quantum teleportation and I hope to God that we never start using it on large scales.

Why aren't you impressed with wormholes, voltage? Is there something about wormholes that I don't know about? The way I understand it is that you would just pull two points in space so that they would be right up against each other. Of course, that would be very hard to do and then there's the issue of keeping it open. I heard it takes a tremendous amount of energy to actually keep one open. But besides that, what would be wrong with a wormhole if we were ever able to create one and keep it open so that people could go through it?

The fact that they call it teleportation has probably irked more people on this forum than you could imagine, because people then visualise some sort of Star Trek event where matter dematerialises and rematerialises elsewhere, in quantum teleportation though the only thing that is teleported is information, not matter or energy.

In an ideal world the scientists who first observed this phenomena would of called it quantum information teleportation, but unfortunately they didn't thus the misguided opinions.

Correct me if I'm wrong, but Quantum "Teleportation" is about the teleportation of INFORMATION not actual particles.
Its more like assume you have two imaginary particles. One is red, one is blue. There is a rule that when put inside of this special container they become the same color. You dont know which. Then you split the particles up and take them to the other side of the universe.
The particles at that time have a color of 0.5*Blue+0.5*Red. Its 50/50. So you dont know. The information is lacking. When you measure one, you know the other. So what happens is "information" about the distant particle is "measured" faster than light. You collapse its probabilities into a single probability. So the particle doesnt transport, just information about it does instantly.

or am i way off? Thats what I thought it meant.

Looks like we cross posted, and yes that's exactly what it means Healey, I'm afraid the OP has looked into the topic with preconceived ideas of what sort of teleportation is going on, which is understandable given what teleportation means in popular culture.

Cthugha
I think fax machine. Or looking at the name of the above poster, xerox photocopy.

Not really. Fax machines or xerox photocopies do not destroy the information (or better: the quantum state), which is transported from a to b, at position a. Quantum teleportation does.
You can't produce a perfect copy of an arbitrary unknown state.

Point taken Cthugha. I've got a shredder at home too. Seriously though, I think the whole concept of teleportation is dubious. The popular science insistence on a destructive "reader" is a plot convenience to avoid a whole panoply of issues such as storage or multiple copies. I work in IT, and I can envisage a software glitch pumping out another copy of Kirk every ten seconds. I guess I'm saying that whilst "teleportation" is an attractive name in the QM arena, I think it's the wrong one. As for what the right name is, I can’t say. If I could, I'd be writing a paper on Quantum Entanglement.

Why aren't you impressed with wormholes, voltage? Is there something about wormholes that I don't know about? The way I understand it is that you would just pull two points in space so that they would be right up against each other. Of course, that would be very hard to do and then there's the issue of keeping it open. I heard it takes a tremendous amount of energy to actually keep one open. But besides that, what would be wrong with a wormhole if we were ever able to create one and keep it open so that people could go through it?

Liger: In my view a wormhole is an impossible abstraction because it allows time travel. I have a strong opinion on this. I’ve thought a great deal about it, and feel that time travel is a hugely impossible abstraction. Like teleportation it's great fun and good entertainment, but it's science fiction not science.

did we find the theory of everything?

The "teleportation" of information with entangled particles has been shown in the lab, as well as the capturing and delayed release of photons in a BEC. To compare quantum entanglement to a Star Trek transporter is a stretch, especially since scientists haven't yet connected the quantum world to classical world. The idea of transporting a package or a human is exciting, but as anyone who has ever looked at theories of such a device knows it would require a MASSIVE amount of energy to even transport something even the size of a bug. To entangle every particle in the bug would require energy and precision not yet available to labs.

Don't let the term "teleportation" fool you. It is a cute, headline grabbing term used for a very real concept in physics.

did we find the theory of everything?

The "teleportation" of information with entangled particles has been shown in the lab, as well as the capturing and delayed release of photons in a BEC. To compare quantum entanglement to a Star Trek transporter is a stretch, especially since scientists haven't yet connected the quantum world to classical world. The idea of transporting a package or a human is exciting, but as anyone who has ever looked at theories of such a device knows it would require a MASSIVE amount of energy to even transport something even the size of a bug. To entangle every particle in the bug would require energy and precision not yet available to labs.

Don't let the term "teleportation" fool you. It is a cute, headline grabbing term used for a very real concept in physics.

Liger: In my view a wormhole is an impossible abstraction because it allows time travel. I have a strong opinion on this. I’ve thought a great deal about it, and feel that time travel is a hugely impossible abstraction. Like teleportation it's great fun and good entertainment, but it's science fiction not science.

What about the whole Special Relativity time dilation thing? Couldn't that be considered time travel? Keep in mind that Special Relativity time dilation isn't just some theoretical concept. It has been experimentally verified.

No? What do you mean by time travel? You can never go BACK in time as far as we know. You can go FORWARD in time, just go to the top of a mountain for a few years and come back down, youll be a few microseconds younger than you should be.

If you want to travel 2 hours into the future just take a quick nap.

It seems that you can experience time almost at any speed that you want so long as its a positive multiple of the current rate.

The "teleportation" of information with entangled particles has been shown in the lab, as well as the capturing and delayed release of photons in a BEC.

Hmm. I'm not a quantum physicist (and I do wish one would would jump in and set us straight), but I think the key thing here is that it's the 'quantum state' which is 'teleported', and I am not sure that this is technically the same as 'information' being teleported. The state remains 'unknown' and isn't considered as "information" until it is observed or the entangled particle otherwise interacts with another, resulting in its state being 'determined'. At least, this is how I have to understand it, as relativity forbids information traveling faster than light as well, not just matter/energy. And while is may seem, on the surface, that "information is traveling faster than light", it's not really the case; locally, the information about the state of the entangled particle(s) is transferred normally, and the only thing transferred any distance is an unknown 'state'.

Understand, I'm not entirely pleased with this way of looking at it either, but it does create a scenario where one's more easily able to suspend ones disbelief.

It could also be that we're just looking at spacetime somehow 'wrongly' and that 'distance' and 'time' and changes as measured by them (eg. motion, etc.) can also occur in ways currently ungrokked. I tend to doubt that even more, though (at least in this context), hence I'd rather entertain the way of looking at it described above.

To compare quantum entanglement to a Star Trek transporter is a stretch, especially since scientists haven't yet connected the quantum world to classical world. The idea of transporting a package or a human is exciting, but as anyone who has ever looked at theories of such a device knows it would require a MASSIVE amount of energy to even transport something even the size of a bug. To entangle every particle in the bug would require energy and precision not yet available to labs.

I think not available even in principle; the computational requirements would be just too huge - one may as well walk to where you want to go. While some theorize that such a computation would be trivial for a quantum computer, I'm less certain (in part because I suspect that, for practical purposes, quantum computing is going to hit insurmountable dead ends and turn out to be not very practical for useful computations - but this could be a wrong assumption.).

But let's suppose it someday will be possible to teleport by quantum means some complex/composite object; I think it's likely that this would involve the destruction of the 'original' object at point A, and recononstruction of a duplicate of it at point B. Even given that the duplicate is an EXACT copy, down to the quantum states of each atom and particle within it, would it be the SAME object? Sure - technically. But you'd not get ME into that teleporter; I don't think that what consitutes THIS particular instance of me would survive the trip, and while an identical copy of me...with all my memories and so forth would be walking around, it still wouldn't be THIS me.

One way to also look at it would be, say, in case the teleportation is non-destructive of the original, and the only 'effect' is a duplicate of the original being created at the backend. I'm not sure I'd even be comfortable with that scenario, and still, "I" wouldn't have gone anywhere. At best, it would be useful for transferring materials or objects, but for people - at least if we decide to retain value for a given instance of a person - well, I think that will be a tough sell.

But this is still highly hypothetical - I don't personally think we'll be dealing with those issues on a practical level for a loooong time, if ever. There are simply too many practical obstacles to overcome beyond the computational and theorectical ones.

For one example, suppose you could entangle particles in a system with other particles at a distance; how do you collect and assemble those distant particles in one place in the same manner as the original? I don't think 'new particles' would be created out of empty space; what if the distant ones are scattered throughout space? (put Alice in teleportation chamber; press entanglement button; press teleport button; teleportation 'happens'; Message to Bob - "Oopsies! Looks like Alice's particles are now spread over a volume of space in a sphere about 40 light years across. But hey, it worked!" )

Don't let the term "teleportation" fool you. It is a cute, headline grabbing term used for a very real concept in physics.

Sure. Spontaneous entanglement/teleportation of a single particle state is one thing. When you talk about the quantum states of 'systems' of particles, you increase the computational complexity ridiculously; even nature doesn't seem to have a lot of interest in pursing that complication, and perhaps we should take a hint. :rofl:

Please understand, I'm not trying to be authoritative here - this is just my take, and I'm sure it's a pretty naiive one at that. I'm just a layperson myself, and though I don't consider myself overly stupid, I recognize I lack a lot of the tools needed to deal with the subject any more deeply than at a superficial conceptual level. That said, I DO think the concepts ARE accessible, but still...they are not necessarily easily so.

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xantox
Gold Member
I am not sure that this is technically the same as 'information' being teleported.
It is quantum information, which has rather different properties than classical information.

Even given that the duplicate is an EXACT copy, down to the quantum states of each atom and particle within it, would it be the SAME object? Sure - technically. But you'd not get ME into that teleporter; I don't think that what consitutes THIS particular instance of me would survive the trip, and while an identical copy of me...with all my memories and so forth would be walking around, it still wouldn't be THIS me.
In this case you should worry about living altogether, since the particles and atoms of your body are constantly replaced with new ones, at a ludicrous rate. So that even if you travel classically, the atoms arriving at destination are by no means the same as the ones departing.

It is quantum information, which has rather different properties than classical information.

Well, point taken, and perhaps, semantically, what I naiively mean by "quantum state" is what is equally embodied by the term "quantum information" (if one makes a distinction between that and "classical" information)?

In this case you should worry about living altogether, since the particles and atoms of your body are constantly replaced with new ones, at a ludicrous rate. So that even if you travel classically, the atoms arriving at destination are by no means the same as the ones departing.

I understand what you mean (and I am not sure this is exactly true, but then in one sense, it could be (as particles change state continuously - that could be looked at AS them changing, and you could mean this in a more literal sense, too), but I think there's a qualitative difference here of scale/scope. There's not a one time, simultaneous en masse exhange (even if it occurs constantly with all particles, I don't think they do it in lock-step), and this allows a certain degree of continuity and integrity to be maintained in the total quantum state of the system that is "me" to be maintained. Is this "important"? I dunno. To "me" it seems to be. (Remember, I'm "naiive").

This gets into a bit of a different discussion, however, that has as much to do with philosophy and the natures of reality and self/being as it does with quantum physics.

Let me pose YOU the question: If such a process as quantum teleportation WERE possible with regards to large complex objects, would you volunteer to be teleported? If yes, why? If not, why not?

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Correct me if I'm wrong, but Quantum "Teleportation" is about the teleportation of INFORMATION not actual particles.
Its more like assume you have two imaginary particles. One is red, one is blue. There is a rule that when put inside of this special container they become the same color. You dont know which. Then you split the particles up and take them to the other side of the universe.
The particles at that time have a color of 0.5*Blue+0.5*Red. Its 50/50. So you dont know. The information is lacking. When you measure one, you know the other. So what happens is "information" about the distant particle is "measured" faster than light. You collapse its probabilities into a single probability. So the particle doesnt transport, just information about it does instantly.

or am i way off? Thats what I thought it meant.

This is 'sort of' how I understood it (and sort of how I tried to explain it in a previous post). But in this case, it's not even information about the 'colors' that 'travels' - the 'quantum state' (or color, in this case) of them is the same; when a distant observer observes one, the knowledge of it's color is transmitted to him normally and by knowing both particles share the same state/color, he knows that the other is the same. Now, there's no way he can tell his colleague observing the other particle what color it is beforehand (unless the other waits for a message to travel normally from his colleague before observing, in which the 'information' about the state is still traveling 'normally' (or classically)).

Now, I suppose, using the same mechanism, the first observer could send a quantum message to his colleague informing him about the state/color of the particle that the second reads before observing, but that's not quite the 'same thing', I think.

Is this far off? I expect you know the answer to this better than I - I'm just trying to see if I have at least a fair 'basic' understanding here through such examples and extrapolating.

xantox
Gold Member
what I naiively mean by "quantum state" is what is equally embodied by the term "quantum information" (if one makes a distinction between that and "classical" information)?
Quantum information is carried by the state of a quantum system (like classical information is carried by the state of a classical system).

(as particles change state continuously - that could be looked at AS them changing, and you could mean this in a more literal sense, too)
This happens literally, eg more than 98% of our body atoms are replaced by new ones every year (through eating, drinking and breathing).

Let me pose YOU the question: If such a process as quantum teleportation WERE possible with regards to large complex objects, would you volunteer to be teleported? If yes, why? If not, why not?
Our beliefs need not be rational. I don't like to travel in airplanes, but this is not evidence of lesser safety than say biking in the city. The rationale here is that, if the process was guaranteed error-free, then a teleportation would be the -only- possible way to arrive at destination still being "the same". Eg. if you can't call "you" the teleported person, then you should have even fewer reasons to call "you" the person biking there. This also means that subjectively a teleportation would be always instantaneous, even if it would always have a duration for external observers.

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Okay, well, part (a large part) of the issue here for me in continuity, and this seems to be the issue we differ on. The process you describe regarding the turnover of atoms is a physcial and gradual change over time and is a well-known/established process, and not really the same as the wholesale and simultaneous destruction/replacement/translation of all an objects elementary particles and their quantum states.

I think a mind/self requires continuity to maintain it's integrity. If you suddenly switch it of and switch it back on again, you wind up with two separate, but identical instances (entities). This is a bit simplistic, mainly because a) I'm not a scientist, and b) although I do have a fairly good grasp of what I am talking about (I think), a detailed explaination would involve getting into a number of issues, from neuroscience and cognitive psychology, perhaps some computer science, touch on various physical sciences, and move on up through various philosophical discussions in order to support my assertions.

I do understand what you're saying; I just maintain a differing interpretation/viewpoint as to what any instaneous and complete "quantum teleportation" of living/intelligent entity (assuming it's possible) means at a sort of existential level.

I am certain that the entity so transported would certainly believe he's the 'original' and there would be no way to prove to him otherwise unless the logic was unassailable (eg. the continuity issue can be proven logically and scientifically to be "so" in a manner he'd have no choice but to accept).

I simply refer to a slight modification of the analogy: suppose both the original and the duplicate continue to exist after such a translation; I really doubt "I" would be aware to "two me's" (or percieve myself being in two locations), one where I am now, and the the other at point B.

I'm not sure how to prove it, but I think it is doable. I think maintaining the unique integrity of a mind through continuity of operation is a vital part of maintaining a sense of self, even if that 'integrity' is degraded to some degree (say, through intoxication, sleep, etc.) from time to time, provided it's never completely broken, it remains.

This is not to say a 'new' but identical instance of the self could not be recreated if a brain or mind could be totally stopped and then restarted, but...I think it would still be 'unique' and separate from the original.

This is a bit off the topic and out of the realm of 'pure' physics (well, maybe, maybe not!), so I'll stop for now. Just wanted to try to explain myself better...

Thanks, though!

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ZapperZ
Staff Emeritus
There are several misconception about entanglement and "quantum teleportation" here. Please note that none of us are free to redefine the meanings of the terms that are being used here. This thread is also starting to meander around outside the realm of the physics. Please stick to the physics issues since we are still in the physics section of PF.

For those who are not well versed in what is meant by "quantum teleportation" and what exact quantum mechanical principles are involved, please familiarize yourself by reviewing these two sources below. If not, we are going to start mutilating things into unrecognizable forms.

http://physicsweb.org/articles/world/11/3/9/1
http://arxiv.org/PS_cache/quant-ph/pdf/0302/0302114v1.pdf

Zz.

Thanks for the info - I'll check out the links to double-check/upgrade my understanding. I don't think I was trying to redefine any terms (and if I was, it was unintentional), though, to be fair; I was simply expressing my iterpretations of the implications of 'practical' quantum teleportation (not that I believe it's going to happen any time soon, if ever).

But I do agree - the discussion's meandering. and it's largely my fault. Sorry....!

xantox
Gold Member
I think a mind/self requires continuity to maintain it's integrity. If you suddenly switch it of and switch it back on again, you wind up with two separate, but identical instances (entities).
There are arguments against this view, but going through them would call for a lengthy discussion which seems quite off-topic in this forum.

I simply refer to a slight modification of the analogy: suppose both the original and the duplicate continue to exist after such a translation; I really doubt "I" would be aware to "two me's" (or percieve myself being in two locations), one where I am now, and the the other at point B.
Two persons are two persons, eg as soon as they are two they start having different histories and so cannot be identical. One will live your possible future if you would stay in A, the other will live your possible future if you would go to B.

There are arguments against this view, but going through them would call for a lengthy discussion which seems quite off-topic in this forum.

Of course; arguments for and against.

Two persons are two persons, eg as soon as they are two they start having different histories and so cannot be identical. One will live your possible future if you would stay in A, the other will live your possible future if you would go to B.

This is pretty obvious, and not lost on me - but it's not like you can choose. The issue is, the tp-ed person (person B) is a 'different person', regardless of whether or not both continue to exist; the original's (person A's) history ends at time of tp (should be be destroyed), or continues as if nothing happened, if not; person B continues his own separate 'history' from that point, although he shares person A's history up until that time (in his mind, at least).

But this off topic, and agree it should stop here.