Quantum Teleportation: Is It Possible?

[benzun_1999]

Quantum teleportation...

Dear reader,
I was just wondering weather Quantum teleportation would ever come into existence. I believe it will be like an fax machine. I will be happy if some one would be happy to discuss this topic.
-benzun
All For God.

 

[LURCH]

Do you mean like large-scale? Not sure if you've heard, but quantum teleprotation of a few photons has already been done. Pretty exiting stuff!

As for teleporting human-sized objects (like for example; HUMANS!), not in my lifetime. Probably not in the lifetime of our youngest member. But I feel certrain that someday we will do it, just because it is the sort of challenge we Homosapiens can't walk away from 'till we've licked it.

 

[jcsd]

It's almost impossible to use quantum telelportation for any practical use, I highly doubt that it could ever be used to teleport any macroscopic object as you still have all the problems of classical teleportation (i.e. that is if you were to ignore quantum effects), plus a few more created by quantum effects. Perhaps I am being overly-pesimistic but it's so hard to see a way around these problems.

 

[benzun_1999]

i feel....

I read about the teleportation of Photons in Australia. Even if teleportation comes into existence I believe that many would not be interested to use it because it would destroy the original and create a copy of it. So eventually the original will be destroyed. Quantum teleportation will be impossible without a computer better than the super computers we have.

-benzun

 

[PRodQuanta]

I think the problem that arises with teleporting a large sum of atoms, like ourselves, is decoherence.
Paden Roder

 

[Ironsun]

Quantum Teleportation

"QT" Would not be a viable means of travel. However we might be able to set up a telegraph style messaging service for real time communications within our own solar system.

 

[benzun_1999]

Originally posted by PRodQuanta
I think the problem that arises with teleporting a large sum of atoms, like ourselves, is decoherence.
Paden Roder

What do you mean decoherence?

-benzun
We all are here for knowledge.

 

[jcsd]

Originally posted by PRodQuanta
I think the problem that arises with teleporting a large sum of atoms, like ourselves, is decoherence.
Paden Roder

Probably the biggest problem of many. all QT really does is to get rid of any problems that would be caused by the 'no clone theorum' in quantum mechanics, you still have neraly all the problems you would have if you were going to consider teleporting from a non-quantum point of view.

Ironsun, I don't see how QT could be used for communications as it requires that you have a classical method of communication in order for it to work.

 

[StarkyDee]

Not sure if you've heard, but quantum teleprotation of a few photons has already been done.

I have heard that the protons weren't actually transported, but they were exactly replicated in 2 different places. Meaning mirror images of the photon, which can't be independent of each other.. maybe I'm wrong, but I will research it and get back..

 

[MythioS]

the communication is something that interests me though. I don't have a huge physics background to understand the nueances of what I've heard but what is all this about taking two particles, seperating them huge distances, and then having both know theyre spin?

this is totally a side topic but wouldn't that be the instant solution for our communication problems if we ever go to mars,etc?

MythioS

 

[selfAdjoint]

Welcome to the Physics Forums, Mythios!

We ought to have a FAQ on this, because confusing stories are spread throughout the media and web.

There are two different issues here.

1) Entanglement. Key words, Bell's inequality, EPR theorem

It's possible to generate a pair of particles which are entangled in the sense that if one of them has spin "up" along a particular line then the other must have spin "down" along that same line. This relationship remains even though the particles are separated, as you say, by vast distances. So everyone thinks, all I have to do to send a bit across that gap is to switch the spin of Particle A (there are ways to do that). And then my friend who is watching Particle B will see it flip and register that bit. Then all I need is a steady stream of entangled particles to be able to send messages.

It doesn't work. The particle can also flip naturally (called "decoherence"). And one flip is all you get; any "measurement" including a natural one, destroys the entanglement. Since you don't know whether the particle is still entangled or not, you can't use it to send messages. What remains is a statistical properety: the states of the particles are more highly correlated due to quantum entanglement than they would be in a classical theory.

EPR is Einstein, Podolski and Rosen, who predicted a closely related effect in around 1940. Bell is the late John Bell, who was a physicist at CERN and developed his correlation inequality in the 1960s.

2) Quantum Teleportation.

Scientists have successfully used quantum mechanics to "teleport" particles (one time a photon, another time an electron) across a short distance. The process involves destroying the particle at its original place and recreating it elsewhere. This is expected to be a much used technique in quantum computing. So far the technique only works on elementary particles. If you see news that they have teloported a proton, you can expect that an atom will be not far behind.

 

[cajones]

You would have to contain the particles in question and be able to alter their spin and such. If one is lost, then the other goes hay-wire. However, some experiments have been done that showed that photons can be slowed and stopped in super cool sodium and stopped by a laser beam, then reactivated later with another laser beam and all of the properties of the photon are kept. I'm not sure but this might help when combined with the instant communication issue.

As far as the teleportation of large objects, i can't really say if we can do it. Many things that were once called impossible have been done, and with photons and information able to be transmited like this, it could be a matter of time before large quantities of matter are sent instantly from the ground to the deck of a space ship. The thing is, it'd probably require enormous amounts of energy, and, until we upgrade our civilization status, energy is going to be a costly part of research.

 

[alias25]

i heard that they have done experiments on teleportion
but by the time they replicate half of the object by obtaining
data about the atoms its made of etc the other half
gets destroyed?

 

[netcrazy]

The reat of the story

@ www.speedypc.20m.com[/url][URL=http://www.speedypc.20m.com]Quantium Physics and beyond [/URL]

 

[notwithstanding]

Originally posted by benzun_1999
Dear reader,
I was just wondering weather Quantum teleportation would ever come into existence. I believe it will be like an fax machine. I will be happy if some one would be happy to discuss this topic.
-benzun
All For God.

I have no idea why one would want to fax a rain shower to someone else unless the divining rod quit working. As far as the generic 'teleportation' issue is concerned, find a few nice sci-fi novels and curl up for a nice night of fiction.

 

[cajones]

...? Which means...


The thing about teleportation that confuses me, is that we are assuming that "The original is destroyed in the process". Isn't actual teleportation the instant movement of one body to another location in space without passing through the space between those two points? So there wouldn't be destruction involved, just movement thatm ignores points that are between the start and end. If that is considered destruction of the original, then would it not logically follow that movement in general could be considered destruction as well, since the object doesn't exist with the same values as before?

 

[selfAdjoint]

If you don't have a continuum of intermediate values, you do have an identity problem: is the individual at the arrival point the true same one who was at the jumpoff point?

In the case of the quantum teleportation experiments there is a definite answer. They definitely destroy the particle at one point in order to create a new one "identical" to the old one at some other point. And yes, they did avoid travel through intermediate space.

 

[ranyart]

There is another possibility?, and that is of Quantum Entanglement?..oops sorry DickT I just scanned your definations in a previous reply!

 

[LURCH]

Originally posted by selfAdjoint
If you don't have a continuum of intermediate values, you do have an identity problem: is the individual at the arrival point the true same one who was at the jumpoff point?

In the case of the quantum teleportation experiments there is a definite answer. They definitely destroy the particle at one point in order to create a new one "identical" to the old one at some other point. And yes, they did avoid travel through intermediate space.

I think the identity problem lies in the meaning of the word "identical ". If the only existence a material object has is the sum total of the information that describes that object, then the fact that the object materializing at "point B" is described by all the same information as the object that dematerialized from "point A", means that it is in fact that same object. If that is the case, then the original was not destroyed, but simply relocated, and no new object has been created.

 

[selfAdjoint]

Originally posted by LURCH
I think the identity problem lies in the meaning of the word "identical ". If the only existence a material object has is the sum total of the information that describes that object, then the fact that the object materializing at "point B" is described by all the same information as the object that dematerialized from "point A", means that it is in fact that same object. If that is the case, then the original was not destroyed, but simply relocated, and no new object has been created.

Yes, I have to agree, although I have personal problems with the conclusion. It reduces the past to the recorded engrams (hated l.ron word) of experience in the current state. So if that is preserved, identity is preserved, and there is no deeper identity than that. Correct. Ugh.

 

[dlgoff]

Originally posted by LURCH
...the original was not destroyed, but simply relocated, and no new object has been created.

Originally posted by selfAdjoint
Yes, I have to agree...

This is so fascinating. Am I correct in thinking/visualizing the QM connection in this way?

When a particle is emitted, the wave function would be like an expanding balloon; the amplitude at each point on the surface being equal. When an observation/detection is made at some point on that surface as it expands outwardly, the balloon deflates making the particle appear there. Now with two entangled particles the balloons would be superimposed so both particles will have equal chance of being at both locations; until observed.

Thanks for any help to bring understanding.

 

[selfAdjoint]

Originally posted by dlgoff
This is so fascinating. Am I correct in thinking/visualizing the QM connection in this way?

When a particle is emitted, the wave function would be like an expanding balloon; the amplitude at each point on the surface being equal. When an observation/detection is made at some point on that surface as it expands outwardly, the balloon deflates making the particle appear there. Now with two entangled particles the balloons would be superimposed so both particles will have equal chance of being at both locations; until observed.

Thanks for any help to bring understanding.

That's one way physicists have thought of it, although importantly the probability is carried in the whole volume of the balloon not just in the surface, and the balloon doesn't expand, it's just THERE, throughout the whole universe (one of the problems with this interpretation).

One of the best introductory ideas is to consider quantum mechanics in one spatial dimension. Think of a bell curve probability distribution, with declining tails "going out to infinity". The x-axis is postion in the one dimesional universe, x=o is Here. Most of the probability is in the bulge but there are faint tinges of probability at every distance. Now imagine the single hump develops two, like a bactrian camel. And let the two humps move apart, as far as you like. It's still one curve, but has a different shape.

Now you do a measurement, and the whole curve vanishes and two points are distinguished on the x-axis, one for each particle. And the probability that one of the particles is at some value of x is just the height of the curve above that point. Most likely the points will be close to the peaks of the two humps, but not CERTAINLY. That's the quantum uncertaintly.

When I said, the curve vanishes, I meant it. The probability, or amplitude, only exists unitil you observe. When you do observe it conditions what you will see. But at that point it ceases to exist and after the observation an entirely new and different curve will come to be. If you assume the wave is a real thing, then this whole process stinks. This is what they call the measurement problem. One answer is to call the probabiity or amplitude wave function an abstract thing that describes our state of knowledge about the particle(s). There are serious technical reasons for rejecting this interpretation too. But nobody has a really good answer for what is the wave function. That's what keeps the cranks in business.

 

[dlgoff]

That's one way physicists have thought of it, although importantly the probability is carried in the whole volume of the balloon not just in the surface, and the balloon doesn't expand, it's just THERE, throughout the whole universe (one of the problems with this interpretation).

The way I was looking at it, the expansion was due to the velocity of the electron which existing over the surface before the wavefunction collapes. But what you are saying is that the probability exist every where to start with before sending it on its way. This is why the whole volume should be considered with the balloon idea.

When I said, the curve vanishes, I meant it. The probability, or amplitude, only exists unitil you observe. When you do observe it conditions what you will see. But at that point it ceases to exist and after the observation an entirely new and different curve will come to be. If you assume the wave is a real thing, then this whole process stinks. This is what they call the measurement problem. One answer is to call the probabiity or amplitude wave function an abstract thing that describes our state of knowledge about the particle(s). There are serious technical reasons for rejecting this interpretation too. But nobody has a really good answer for what is the wave function. That's what keeps the cranks in business.

So many questions. I hope you don't think I'm one of those cranks. However I can see why people are so interested. Wanting to understand these questions is a driving force.

Anyway if I can ask another question(or two):

I'm starting to understand (better mental vision). Can the wave function(s) of an electron as it drifts between a couple of electromagnetic pole faces (nice parallel magnetic field normal to its path) be defined? i.e. does the placement of the electromagnet count as an observation causing the wave function to collapse (or a continious change during its curved path) with a final collapse at a detector?

Why is it so hard to accept a wavefunction giving probability densities is a real thing? i.e. why does the whole process stink?

Do you have any personal thoughts on how our observations conditions what we'll see?

Thanks selfAdjoint. I've learned a lot from you over the years.

 

[young e.]

yes it might be true but i think for us human size and even much bigger it needs a lot of energy for this matter to came into existence. This might be posibble into the near future

 

[meteor]

Some intriguing words about teleporting that I would like to be given a definition:

Bell measurement
Bell state
qudit

Thanks

 

[selfAdjoint]

A Bell measurement (after the late John Bell, a physicist at CERN) is a measurement of a Bell state. It collapses the state.

A Bell state is an entangled quantum state of two particles such that if the state of one particle is measured (Bell measurement) the state of the other can be determined, even though the particles are separated.

qubit I think this is what you meant. It's a coined word, made up from "quantum" and "bit". It's pronounced "Q-bit" or cubit, like the Ark measurement.

In quantum mechanics the states of a particle can be superimposed. This does not mean added together, exactly nor does it mean mixed, the closest analogy I can think of is the notes in a chord. The notes are not added or mixed, but you hear them together, as a chord, which is something different from playing the notes one at a time (off topic, Schoenberg never seems to have really go this point). A superimposed state of values for one particle is not the same thing as the entangled state of two particles (Bell state).

So now think of "quantum information. The smallest unit of classical information is the bit. The bit can have one of two state, 0 or 1 (or on or off or many different possibilities). A bit is the amount of information you acquire in answer to a question that can be answered yes or no. For example the sex of a person (ordinarily) is coded in one bit.

Now let the two values or alternative of a bit be superimposed, quantum fashion. This is the minimum unit of quantum information: a qubit.

 

[meteor]

Thanks SA for your accurate explanations (like always), but I knew before what is a qubit. Qudit is another different thing, it appears for example in the technique called Qudit quantum state tomography

 

[selfAdjoint]

That was a new one on me, so I did what I always do, I googled. And I found http://www.physics.uq.edu.au/people/andrew/publications/2002/qudittomo.pdf , with a definition. Qubits are mathematically determined by the spin-2 matrices SU(2), and the paper includes that definition with examples. SU(2) consists of 2x2 matrices of complex numbers that are Special in having determinant 1 and Unitary by their adjoints being their inverses. The adjoint is the conjugate transpose, if you follow me.

So then qudits are defined in the analogous way be dXd special unitary matrices SU(d). And where qubits have 2 superposed states it appears qudits can have d superposed states.

 

[Dbever]

Ansible communication?

I have heard the Ansible method discussed in past years where via the splitting of a particle(such as a photon)results in 2 halves which think they are still a whole particle.By taking one half of the particle to a different location it would be possible to use the link between the 2 halves as a conduit for messages.Is this a feasible theory or does the Uncertainty Theory preclude this?As to the QT of living humans i think it would be a long while before we have the computing power to capture a persons holistic wavefront and store along with the relative positions and states of every molecule needed for to translocation.

 

[selfAdjoint]

The method you are referring to depends not on splitting a particle, but splitting an entangled state of two particles. It is possible to produce two particles in a state such that if one is polarized this way, the other is necessarily polarized that way. So if you were to separate the particles, and measured the polarization state of one, you would automatically know the polarization state of the other.

This has been used by science fiction authors to instantiate the old sf idea of the ansible, or instant communicator. The word ansible goes back to the science fiction of the 1960's and has been used continuously ever since.

Would it work? No. The idea is that if you flip the particle here from the orientation you brought it with, to the opposite one, then the other particle, over in the Alpha Centauri system, will also flip - in the opposiite direction, and thus you have sent a bit from here to Alpha, and if you can send bits then you can send messages.

But the particles come to you with every possible orientation. If you flip a random one, the other one is random too, and your message is lost in noise. And how do you know your own particle flipped. You can't know what state it's in - remember they come to you in all possible states - unless you look at it. And here we come to the killer fact:

If you look at either of the particles, if you interact with it in any way whatsoever, you destroy the entanglement

It's called collapse of the wave function. It was the wave function that carried the entanglement.

So you're hoist on the horns of a dilemma. Either you check the particle to see how it's oriented so you can flip it - in which case you have no more entanglement and the bit won't be sent, or you flip it blindly in which case the receiver at the other end can't tell which particle you flipped or which way is a flip.

But maybe you're clever. You say, I won't use random particles, I'll use particles all oriented in a certain direction, by agreement. So I won't have to look first, and my friend on Alpha will know what a flip is. But the process that produces entangled particles produces them with all possible orientations, and there are symmetry arguments that say this has to be. So to get the particles to line up in some fixed way you'ld have to act on them - ooops! there goes your entanglement again!

Bottom line. There ain't no such thing as a working ansible.