A SEMINAR REPORT ON

QUANTUM TELEPORTATION

Submitted by: Ridhima Khurana 1508217 EC4 Submitted to: Mr.Virendra Mehla Ms.Purnima Ms.Pinkle

Department Of Electronics & Communication Engineering N.C. College Of Engineering (Israna), Panipat

Acknowledgement

Apart from the efforts of me, the success of any work depends largely on the encouragement and guidelines of many others. I take this opportunity to express my gratitude to the people who have been instrumental in the successful completion of this project.

I would like to show my greatest appreciation to Mr. Virender Mehla, Ms. Purnima and Ms. Pinkle. I cant say thank you enough for their tremendous support and help. I feel motivated and encouraged every time I attend their meeting. Without their encouragement and guidance this work would not have materialized.

The guidance and support received from all the members who contributed and who are contributing to this work, was vital for the success of the work. I am grateful for their constant support and help.

Ridhima Khurana

QUANTUM TELEPORTATION

Abstract
Quantum teleportation is central to the practical realization of quantum communication. Although the first proof-of-principle demonstration was reported in 1997 by the Innsbruck and Rome groups, long-distance teleportation has so far only been realized in fibre with lengths of hundreds of metres. An optical free-space link is highly desirable for extending the transfer distance, because of its low atmospheric absorption for certain ranges of wavelength. By following the Rome scheme, which allows a full Bell-state measurement, we report free-space implementation of quantum teleportation over 16 km. An active feed-forward technique has been developed to enable real-time information transfer. An average fidelity of 89%, well beyond the classical limit of 2/3, is achieved. Our experiment has realized all of the non-local aspects of the original teleportation scheme and is equivalent to it up to a local unitary operation5. Our result confirms the feasibility of space-based experiments, and is an important step towards quantumcommunication applications on a global scale.

CONTENTS:

1. INTRODUCTION 2. ENTANGLEMENT 3. TELEPORTATION CLASSICAL TELEPORTATION QUANTUM TELEPORTATION 4. 5. 6. 7. 8. 9. BELL STATE MEASUREMENT THE TELEPORTER EXPERIMENTAL ANALYSIS TELEPORTATION OF PHOTONS WITHOUT DESTRUCTION CAN THE ATOMS BE ENTANGLED TOO QUANTUM TELEPORTATION USED FOR SUPERLUMMINAL COMMUNICATION 10. REAL EXPERIMENTS THAT DO TELEPORTATION 11. HUMAN TELEPORTATION 12. DECOHERENCE 13. APPLICATIONS OF QUANTUM TELEPORTATION 14. THINGS TO COMBAT 15. CONCLUSION 16. BIBLIOGRAPHY

Introduction
Quantum Teleportation is an exciting new area of physics that deals with teleportation of sub-atomic particles and photons. On hearing the word teleportation, the first thing that comes to our mind is the Star Trek movie,in which a machine took captain Kirk from one place to another instantaneously without having to physically travel the distance . Basically, quantum teleportation is a bizarre shifting of physical characteristics between the natures tiniest particles, no matter how far apart they are. What actually happens is what Einstein called spooky action at a distance. This is made possible by entangling quantum particles. So, no matter how far apart the particles are, if you do something to one entangled particle, it will have the same effect on the other. The spookiness is that the particles carry information about the interaction, despite the distance between them. Quantum entanglement neither requires the entangled particles to come from a common source nor to have interacted in past.

a scene from star trek

What is Entanglement?
Entanglement is a property of atomic particles in which two particles at a great distance are in some way intertwined, i.e. any effect on one particle is simultaneously felt in the other particle as well. Entanglement involves a relationship between the possible quantum states of two entities such that when the possible states of one entity collapse to a single state as a result of suddenly imposed boundary conditions, a similar collapse occurs in the possible states of the entangled entity, no matter where or how far away the entangled entity is located.

This can be expressed in a simpler way with respect to photons. When two photons are entangled, they have opposite luck. Whatever happens to one photon is the opposite of what happens to the other. In particular, their polarizations are the opposite of each other. If two quantum particles are entangled, a measurement on one particle automatically determines the state of the second even if the particles are widely separated. Individually, an entangled particle has properties (such as momentum) that are indeterminate and undefined until the particle is measured or disturbed.

Teleportation
In Star Trek, when Captain Kirk is beamed from the starship Enterprise to the surface of a planet, Captain Kirk de-materialises on the Enterprise, and then re-materialises on the planet. On the TV show, an unanswered question is whether the transporter physically disassembles Captain Kirk, moves the atoms from his body to the planet, and then reassembles them. Another perhaps more reasonable alternative would be to scan all the information about Captain Kirk's physical state, and transmit that information to the planet surface where it is used to construct a new Captain Kirk out of raw materials found on the planet. Note that in either case the transporter needs to have complete information on Kirk's physical state in order to reconstruct him. However, the Heisenberg Uncertainty Principle means that it is impossible to obtain this complete information about Kirk. Thus, it seems that the best the transporter can do is make an approximate copy of him on the planet surface. Quantum Teleportation provides a way to "beat" the Uncertainty Principle and make an exact copy. As we shall see, the mechanism that beats the Uncertainty Principle is the same one used to beat it in the Quantum Correlation experiments we examined when we discussed Bell's Theorem. We shall also see that although the collapse of the state for the two measurements in the correlation experiments occurs instantaneously, the teleportation can not occur faster than the speed of light. Before we were discussing Quantum Correlation experiments in which we were measuring the spins of two separate electrons whose total spin was zero. We call the states of those two electrons entangled. What is teleportation? Roughly speaking, there is a Lab A and a Lab B, and each lab has a box. The goal of teleportation is to take any object that is placed in Box A and move it to Box B. Of special interest to science fiction fans (among others) is human teleportation, where a brave telenaut (whom we shall call Jim) enters Box A and uses the teleportation machine to travel to Lab B. It turns out that human teleportation appears possible in principle, though is probably impossible in practice. Nevertheless, teleportation of much smaller objects like individual spins is not only possible, but has been accomplished in the laboratory. Our goal here is to explain both how teleportation is done and why it is interesting.

Classical teleportation
Let's start by assuming that the world is perfectly classical, that is, let's not worry about the effects of quantum mechanics. Can we do teleportation? As stated above the problem is trivial and the solution is called a truck. We load the cargo of box A onto a truck, we drive the truck over to lab B, and unload the cargo into box B. Presto exchange-o, we have teleportation! But that is not the solution we really wanted, so let's build a wall between labs A and B. Now no trucks can get through. Unfortunately, if this wall is perfect and separates Labs A and B into two different universes, then there is nothing that can be done to move things between the two universes and our poor telenaut Jim will be forever stuck in Lab A. To make the problem both possible and interesting let's allow a single telephone line between universes A and B. We are now in the situation pictured in Figure I. Can we teleport Jim from A to B now? What we are trying to build now is essentially a fax machine. A giant 3-D fax machine, but a fax machine nonetheless. Into the fax machine at A goes Jim and out of the fax machine at B we get a copy of Jim. The first objection that you could raise is that we now have two copies of Jim, which may not be ideal. But this is an easily fixed problem. We buy a shredder and attach it to the fax machine at A so that it destroys the originals after they pass through the fax. So we run Jim through the shredder at A and now there is only on copy at B. Will this be painful for Jim? Maybe (hence the title brave telenaut). But remember that the surviving copy at B was made before the "original" at A was put into the shredder. From the point of view of the copy at B, he entered the box at A and exited at B and no pain was ever felt. A second objection is that we are only getting an approximate copy of Jim at B. Certainly a standard fax machine has a fairly poor resolution, however there is no reason why we can't build very very accurate fax machines. Now it is true that the copy at B will never be perfect. But that shouldn't be a problem. Even if we used a truck to transport an object from A to B, the object that arrives at B would be slightly different from the one that left A.

FIG. 1: The setup for teleportation

Along the way it will be shaken a bit or it might get hit by some cosmic rays which will change the state of a few atoms. Our goal should be that the errors that appear when we teleport Jim via the fax machine should be comparable to the changes that would have occurred when moving Jim in a truck. That is, a few very very small errors should be acceptable. An important thing to notice is that our giant fax machine is not intended to transfer matter and energy, just like a regular fax machine would not be used to transmit blank papers. We always assume that we have the appropriate matter and energy available in Lab B and our goal is simply to assemble it into the pattern of the object placed in Box A. So can we build a classical teleportation device as described? The answer appears to be yes. That doesn't mean that it is easy. It would be an incredible engineering feat to build a giant 3-D super-accurate fax machine. But it really is just a difficult engineering problem. From the point of view of a physicist there is no reason why this shouldn't be possible.

Quantum teleportation
But now we remember that the world is quantum mechanical, and realize that there is a problem... What is the fax machine supposed to do? 1. Fully measures the state of the input 2. Transmits the results via the phone 3. Reconstructs the original from the received description.

Step 1 is already impossible in a quantum world because of the Heisenberg uncertainty principle. We could measure the position of all the particles forming Jim but then we wouldn't get a chance to measure the momentum of those particles. Alternatively, we could measure the momentum but then not the position. One can also envision a mixed strategy where we measure some positions and some momenta, however the uncertainty principle basically guarantees that we will never obtain enough information to rebuild even a modestly good copy of Jim. It appears that even before running Jim through the shredder, the measurement process will likely destroy the only good copy without obtaining the required information to rebuilt Jim anew. The surprising result of quantum teleportation is that even though the "measure and reconstruct" procedure does not work, there is an alternative procedure that effectively realizes teleportation in the quantum world. In fact, it was not until the publication of a 1993 paper by Bennett, Brassard, Crepeau, Jozsa, Peres and Wootters that we realized quantum teleportation was possible. That is some 70 years after the formulation of the theory of quantum mechanics! Effectively we realized that quantum teleportation, which we thought to be impossible, is only very very hard. What is the difference between the two notions? Traveling faster than the speed of light is impossible, traveling at say 99% of the speed of light is possible but very hard to do. The upgrade in status from impossible to very very hard may not be very significant to those who would like to actually build such a device. But to a physicist it makes a world of difference, and is a very exciting discovery. So let me begin by describing the setup for quantum teleportation, which is almost identical to the setup for classical teleportation described above. Again, we will have Labs A and B, each with a box, and we will try to move the contents of box A to box B. The two labs will be separated by a wall and only connected by a phone. We have to be careful in specifying what kind of phone. If this phone allows sending quantum information back and forth, then the problem of quantum teleportation becomes relatively trivial. It is similar to the classical case when we allowed trucks to move objects between A and B. The interesting case is when the phone allows only the passage of classical information. You can think of the phone as measuring all signals as they pass through the phone. All standard phones are classical phones.In effect, what we are asking here is can we use our standard classical communication tools to transmit the state of a quantum system.

Thus far our setup for quantum teleportation is equal to the one for classical teleportation. But there is one important difference. In the quantum case, Labs A and B must begin with something called an entangled quantum state, which will be destroyed by the teleportation procedure. Roughly speaking an entangled state is a pair of objects that are correlated in a quantum way. Below we will describe a specific example known as the singlet state" of two spins. However, let us first explore the consequences of this extra requirement for quantum teleportation. To prepare an entangled state of two particles, one essentially has to start with both particles in the same laboratory, let's say Lab A. Now we have the problem of sending one of the particles to Lab B. In principle, we could use quantum teleportation to send this particle to B, but this process would destroy one entangled state to create another entangled state, a net gain of zero. In any case, we have to worry about how the first entangled state is created. The only solution is that sometime in the past the wall that separates Lab A and Lab B must not have been there. At that time the scientists from the two labs met, created a large number of entangled states, and carried them to their respective laboratories. Think of two friends who lived nearby, but now one is moving away. They can create some entangled states that the friend who is moving can carry with him when he leaves, and then they can use those to teleport things back and forth. However, if they had never met in person and have no friends in common (who could have met with both of them) then quantum teleportation becomes impossible. So returning to our brave telenaut Jim, he will be able to teleport to the labs of his friends. But also he could use two teleportations to travel to the labs of people whom he has never met personally, but who are friends of his friends. Similarly, he can teleport to the labs of the friends of his friends of his friends, and so on. However, teleporting to say a distant planet or to some other place we have never had contact with is impossible. The entanglement requirement poses a second problem, since as we mentioned above it is destroyed when used. Entanglement is effectively a resource that is slowly depleted as teleportations occur. It can be renewed by meeting in person and then carrying entanglement back from Lab A to Lab B, but it has to be transported without the use of teleportation. In principle this is difficult, otherwise we wouldn't have bothered using teleportation from A to B in the first place. However, the idea is that one difficult journey from A to B can allow in the future many quick transfers from A to B. I should mention one last important detail of quantum teleportation. In the classical case we decided to run Jim through the shredder in Lab A after faxing him to lab B. But it seems like this step was optional, and we could have chosen to end up with two copies of Jim. In the quantum case this is not possible, because quantum information cannot be copied. The only way to teleport an object to Lab B is to destroy the object at Lab A. Philosophically, one can say that if there can ever be only one copy of Jim at any time, and the copy of B survives the teleportation process in a pain free manner, then whatever is destroyed at in Lab A could not have been a copy of Jim. Our goal below will be to describe the teleportation of the spin of a single electron. That is, we shall place a single electron in Box A and a single electron in Box B. The goal is to make sure that the spin of the electron in Box B after teleportation is equal to the spin of the electron in Box A before teleportation. We won't care if the momentum and position

(relative to the box) of the electrons are the same. We shall call this the teleportation of a spin. It may seem like this is a much weaker goal than teleporting the full state (i.e., its position, momentum and spin) of an electron. However the techniques described below can be extended to teleport positions and momenta as well. Furthermore, it turns out that the spin is already a fairly interesting quantum mechanical object. A spin is equivalent to one qubit, which is the quantum generalization of a bit.

Bell-state measurements
In previous discussions we almost always talked about the spin state of electrons, although we regularly pointed out that the same situations exist for the polarization of light, albeit with a difference of a factor of 2 in the angles being used. Here we will reverse the situation, and mostly talk about polarization states for photons, although the arguments also apply to spin states of electrons. The fact that we may talk about light polarization in almost the same way that we discuss electron spin is not a coincidence. It turns out that photons have spins which can exist in only two different states. And those different spins states are related to the polarization of the light when we think of it as a wave.

Here we shall prepare pairs of entangled photons with opposite polarizations; we shall call them E1 and E2. The entanglement means that if we measure a beam of, say, E1 photons with a polarizer, one-half of the incident photons will pass the filter, regardless of the orientation of the polarizer. Whether a particular photon will pass the filter is random. However, if we measure its companion E2 photon with a polarizer oriented at 90 degrees relative to the first, then if E1 passes its filter E2 will also pass its filter. Similarly if E1 does not pass its filter its companion E2 will not. Earlier we discussed the Michelson-Morley experiment, and later the Mach-Zehnder interferometer. You will recall that for both of these we had half-silvered mirrors, which reflect one-half of the light incident on them and transmit the other half without reflection. These mirrors are sometimes called beam splitters because they split a light beam into two equal parts.

We direct one of the entangled photons, say E1, to the beam splitter. Meanwhile, we prepare another photon with a polarization of 450, and direct it to the same beam splitter from the other side, as shown. This is the photon whose properties will be transported; we label it K (for Kirk). We time it so that both E1 and K reach the beam splitter at the same time.

The E1 photon incident from above will be reflected by the beam splitter some of the time and will be transmitted some of the time. Similarly for the K photon that is incident from below. So sometimes both photons will end up going up and to the right as shown. Similarly, sometimes both photons will end up going down and to the right.

But sometimes one photon will end up going upwards and the other will be going downwards, as shown. This will occur when either both photons have been reflected or both photons have been transmitted. Thus there are three possible arrangements for the photons from the beam splitter: both upwards, both downwards, or one upwards and one downwards. Which of these three possibilities has occurred can be determined if we put detectors in the paths of the photons after they have left the beam splitter. However, in the case of one photon going upwards and the other going downwards, we cannot tell which is which. Perhaps both photons were reflected by the beam splitter, but perhaps both were transmitted. This means that the two photons have become entangled. If we have a large beam of identically prepared photon pairs incident on the beam splitter, the case of one photon ending up going upwards and the other downwards occurs, perhaps surprisingly, 25% of the time.

Also somewhat surprisingly, for a single pair of photons incident on the beam splitter, the photon E1 has now collapsed into a state where its polarization is -450, the opposite polarization of the prepared 450 one. This is because the photons have become entangled. So although we don't know which photon is which, we know the polarizations of both of them. The explaination of these two somewhat surprising results is beyond the level of this discussion, but can be explained by the phase shifts the light experiences when reflected, the mixture of polarization states of E1, and the consequent interference between the two photons.

The teleporter
Now we shall think about the E2 companion to E1. 25 percent of the time, the Bell-state measurement resulted in the circumstance shown, and in these cases we have collapsed the state of the E1 photon into a state where its polarization is -450. But since the two photon system E1 and E2 was prepared with opposite polarizations, this means that the companion to E1, E2, now has a polarization of +450. Thus the state of the K photon has now been transferred to the E2 photon. We have teleported the information about the K photon to E2. Although this collapse of E2 into a 450 polarization state occurs instantaneously, we haven't achieved teleportation until we communicate that the Bell-state measurement has yielded the result shown. Thus the teleportation does not occur instantaneously. Note that the teleportation has destroyed the state of the original K photon. Quantum entanglements such as exist between E1 and E2 in principle are independent of how far apart the two photons become. This has been experimentally verified for distances as large as 10km. Thus, the Quantum Teleportation is similarly independent of the distance.

The Original State of the Teleported Photon Must Be Destroyed Above we saw that the K photon's state was destroyed when the E2 photon acquired it. Consider for a moment that this was not the case, so we end up with two photons with identical polarization states. Then we could measure the polarization of one of the photons at, say, 450 and the other photon at 22.50. Then we would know the polarization state of both photons for both of those angles.

As we saw in our discussion of Bell's Theorem, the Heisenberg Uncertainty Principle says that this is impossible: we can never know the polarization of a photon for these two angles. Thus any teleporter must destroy the state of the object being teleported

A teleportation machine would be like a fax machine, except that it would work on 3dimensional objects as well as documents, it would produce an exact copy rather than an approximate facsimile, and it would destroy the original in the process of scanning it. A few science fiction writers consider teleporters that preserve the original, and the plot gets complicated when the original and teleported versions of the same person meet.

Experimental analysis
In 1993 an international group of six scientists, including IBM Fellow Charles H. Bennett, confirmed the intuitions of the majority of science fiction writers by showing that perfect teleportation is indeed possible in principle, but only if the original is destroyed. Until recently, teleportation was not taken seriously by scientists, because it was thought to violate the uncertainty principle of quantum mechanics, which forbids any measuring or scanning process from extracting all the information in an atom or other object. According to the uncertainty principle, the more accurately an object is scanned, the more it is disturbed by the scanning process, until one reaches a point where the object's original state has been completely disrupted, still without having extracted enough information to make a perfect replica. This sounds like a solid argument against teleportation: if one cannot extract enough information from an object to make a perfect copy, it would seem that a perfect copy cannot be made. But the six scientists found a way to make an end-run around this logic, using a celebrated and paradoxical feature of quantum mechanics known as the EinsteinPodolsky-Rosen effect.

In brief, they found a way to scan out part of the information from an object A, which one wishes to teleport, while causing the remaining, unscanned, part of the information to pass, into another object C which has never been in contact with A. Later, by applying to C a treatment depending on the scanned-out information, it is possible to maneuver C into exactly the same state as A was in before it was scanned. A itself is no longer in that state, having been thoroughly disrupted by the scanning, so what has been achieved is teleportation, not replication. As this figure suggests, the unscanned part of the information is conveyed from A to C by an intermediary object B, which interacts first with C and then with A. What? Can it really be correct to say "first with C and then with A"? Surely, in order to convey something from A to C, the delivery vehicle must visit A before C, not the other way around. But there is a subtle, unscannable kind of information that, unlike any material cargo, and even unlike ordinary information, can indeed be delivered in such a backward fashion. This subtle kind of information, also called "Einstein-Podolsky-Rosen (EPR) correlation" or "entanglement", has been at least partly understood since the 1930s when it was discussed in a famous paper by Albert Einstein, Boris Podolsky, and Nathan Rosen.

In the 1960s John Bell showed that a pair of entangled particles, which were once in contact but later move too far apart to interact directly, can exhibit individually random behavior that is too strongly correlated to be explained by classical statistics. Experiments on photons and other particles have repeatedly confirmed these correlations, thereby providing strong evidence for the validity of quantum mechanics, which neatly explains them.

This figure compares conventional facsimile transmission with quantum teleportation. 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 (e.g. paper) to produce an approximate copy of the original. In quantum teleportation two objects B and C 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.

Teleportation of photons without destruction

In June 1999 the act of measuring a photon repeatedly without destroying it was achieved for the first time, enabling researchers to study an individual quantum object with a new level of non-invasiveness. Physicists have long realized that it is possible to perform non-destructive observations of a photon with a difficult-to-execute technique known as a quantum nondemolition (QND) measurement.after many years of experimental effort, researchers in France (Dr Haroche Etal) demonstrated first QND measurement of a single quantum object, namely, a photon bouncing back and forth. Eating up or absorbing photons to study them is not required by fundamental quantum mechanics laws and can be avoided with the QND technique demonstrated by French researchers.

Can the atoms be entangled too?

Atoms also can be entangled. However much complexity is involved in the teleportation of atoms due to their complex structure. Scientists are working towards breaking this challenge. Researchers in Paris have achieved progress at the macroscopic level by entangling pairs of atoms for the first time. As opposed to teleportation of only two states of a quantum particle, such as the polarization of photons, the new research would allow all quantum states to be teleported. Previously, physicists obtained entangled particles as a by-product of some random or probabilistic process, such as the production of two correlated photons when a single photon passes through a special crystal. However, in the deterministic entanglement process for atoms, the researchers trap a pair of beryllium ions in a magnetic field. The experimental apparatus produces two entangled atoms, one atom in ground state and the other atom in excited state, physically separated so that the entanglement is non-local. When a measurement is made on one atom, say, the atom in ground state, the other atom instantaneously presents itself in excited state-the result of second atom wave function collapse thus determined by the result of the first atom wave function collapse.

Can quantum communication?

teleportation

be

used

for

superluminal

If we tried to define a colloquial notion of teleportation it would probably have two main properties: That objects move from A to B without passing" through the space in between and that it be done instantaneously, or at least very very fast. Roughly speaking, our teleportation schemes satisfy the first property. However, thus far we haven't discussed the speed at which teleportation should occur.

Teleportation as defined here requires sending a message from Lab A to Lab B using a regular phone. The message will travel at the speed of light from A to B. Therefore, our version of teleportation cannot be instantaneous and does not allow for travel faster than the speed of light. In fact, teleportation might be significantly slower than light travel if the measurement and reconstruction procedures are slow.

However, if we are teleporting a person (or some other system that is not static) then the measurement and reconstruction procedures need to be performed nearly instantaneously. After all, if you get to see as your feet are slowly measured and disassembled, the process would likely not be pain-free. At first glance, though, there seems to be a way to use the teleportation procedure for superluminal communication. That is, by measuring the spins in Lab A, we are somehow instantaneously modifying the spin in Lab B. Whether or not this is a good description of what is going on depends which interpretation of quantum mechanics is used to describe the system (there are actually many interpretations of quantum mechanics which describe the above process in very different ways). However, all interpretations of quantum mechanics agree on one fact: that such tricks cannot be used for superluminal communication. The basic idea of such a proof is to check that, when averaged over all the outcomes obtained in Lab A, any measurement done in Lab B will always yield 50-50 outcomes, no matter what state is being teleported. Therefore the measurements in Lab B cannot convey any useful information, at least until such a time when the correction operators have been applied. Unfortunately all modern theories of physics predict that both faster than light travel and faster than light communication are impossible.

Real experiments that do teleportation

A number of groups conducted experimental realizations of the quantum teleportation procedure described above in the years 1997 and 1998, using a variety of different systems such as the spin (or polarization) of photons and the spin of atoms. In many cases Labs A and B were the left and right side of a table, and the spins were teleported roughly 50 cm. The reason distance becomes relevant has to do with the distribution of entanglement which becomes harder as the separation between the two labs increases. A second related problem is the storing of entanglement which can only be done for very short periods, so in practice most early experiments distribute the entanglement only moments before it is to be used for teleportation. However, these experiments were sufficient to convince most physicists that teleportation of spins is possible. Since 1997 there have also been many improved versions of the teleportation experiment. For instance, the distance has been increased in one experiment to 600 m, and the accuracy of the teleported state has also been slowly improving. In principle, if you can teleport one spin, then you can teleport many spins simply by repeating the experiment in series many times. But this roughly only works on disjoint spins. To teleport a single object comprised of many spins is still out of reach of present day experiments.

In the future, though, we should see experiments that teleport large numbers of spins. Certainly, if a practical quantum computer is ever built then the same technology would likely allow us to teleport a few thousand spins. It is likely that this will happen within the next 30 to 50 years, if not sooner.

Human teleportation

Teleportation is the name given by the science fiction writers to the feat of making an object or person disintegrate in one place while a perfect replica appears somewhere else. Human teleportation would require a machine that measures the position, velocity, and type of atoms throughout the body of a person and then sends that information ( say, through radio waves) to the place where the body is reconstructed by another machine. The main three sub-atom constituents would be free radicals, quantum effects in the neurons of the brain, and photons. Taken one at a time, free radicals would not be a major problem and their possible loss may not affect any part of the anatomy. Bottlenecks. The visible human project by the American National Institute of health requires about 10 GB (=1011=100,000,000,000 bits, i.e. about ten CD-ROMs) to give the full three-dimensional details of a human down to one-millimeter resolution in each direction. If we forget about recognizing atoms and measuring their velocities and just scale that to a resolution of one atomic length in each direction, the information amounts to about 1032 bits. This information is so large that even with the best optical fibers conceivable it would take over a hundred million centuries to transmit all the information! There are some 1029 matter particles comprising a human person, each of which has position and momentum degrees of freedom in addition to spin. In principle, we might also need to teleport the photons, gluons and other energy particles comprising a person.

Teleporting all that is going to be significantly harder than a few thousand spins. It is probably a good guess that teleportation of humans will never be possible. Are we at least sure that it is possible to teleport humans in principle? While most scientists expect that ten, hundreds and maybe even thousands of spins will be teleported in practice some day, the teleportation of a human being, even in principle, is actually still a controversial subject. I would roughly divide people into three schools of thought. The first group of physicists would argue that there is a soul, consciousness or spirit that permeates the human body that cannot be described by science. Unfortunately, in this view by definition we are prevented from using science to determine if teleportation is feasible. A second group of physicists would disagree with human teleportation because of something known as the measurement problem. Roughly speaking, any object that is capable of performing quantum measurements cannot itself be a quantum object, and therefore cannot be teleported using quantum teleportation. In this view, small numbers of particles are quantum but at some point when you combine enough particles you end up with a classical or observer object, which cannot be described by the laws of quantum mechanics. In principle, such a belief will have experimental consequences, as we should be able to determine at what point do objects stop being quantum mechanical. At the moment there is neither any experimental evidence for such observer objects nor even a consistent theory that could describe them. On the other hand, it is also true that presently it is very hard to experimentally study large quantum systems, and so it is quite possible that something interesting will happen when a large enough system is examined. The third school of thought (which I am partial to) would say that all objects big and small are quantum mechanical, and therefore in principle can be teleported. What happened with the measurement problem? I would argue that measurements never actually occur. What happens is that the observer becomes entangled with the system he is measuring, and this appears to the observer as if a measurement was performed. The mathematics for this process works out quite nicely, but it does leave the nagging question of why does it feel like we are constantly measuring the world? Of course, the final answer to whether teleportation of people is possible even in principle must wait for the formulation of a complete theory of physics, one which unifies relativity with quantum mechanics. In the meantime, one can ask if there any applications for teleporting thousands of spins? The answer is probably yes. In the future it is likely that quantum computers (i.e., computers capable of processing quantum information) will be built and may even be as ubiquitous as classical computers are today. These computers will need to exchange quantum information. One way these exchanges of information can occur is via a quantum phone, that is, a device capable of sending and received quantum messages. But when such phones are not available, the alternative is to do teleportation using a regular phone. So don't be surprised if some day in the next 100 years you see a quantum teleportation device for sale in your local computer store.

Why not objects?

Teleportation of human body as a whole involves lots of complexities. And it may prove to be impossible in the future. But lets not confine our vision of teleportation only to human body. If teleportation proves successful, rigid bodies could be teleported in useful ways. We can teleport objects (non-living things) from one place to another, which involves much less risk. This development may also be expanded towards macroscopic objects because the atomic structural arrangement of their atoms will be comparatively simpler than of human body.

Decoherence
Objects quantum states degrade when information leaks to or from the environment (i.e., environmental noise) through stray interactions with the object. Introduces a certain level of error in the exchange of quantum information between the systems. Fundamentally Limits q-Teleportation.

Applications of quantum teleportation

Quantum computer (computer that has data transmission rates many times faster than today's most powerful computers). Suspended animation (by creating a copy many years after the information was stored). Backup copies (creating a copy from recently stored information if the original was involved in a mishap.)

Things to combat
Difficult to fathom what is future for human teleportation. Effects of the q-Teleportation process on the human consciousness, memories and dreams, and the spirit or soul. Consciousness, memories and dreams, and spirit/soul be successfully and accurately teleported or not?

Conclusion
With the advancements, atoms of size 1012 are entangled and teleported. We are away from being able to teleport and entangle bulky objects( technical equipments, weapon platform, communication devices).

Bibliography
www.wikipedia.com www.google.com