Quantum Teleportation Report

8/2/2019 Quantum Teleportation Report

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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


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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 theirencouragement 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


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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 quantum-communication applications on a global scale.
http://www.nature.com/nphoton/journal/v4/n6/full/nphoton.2010.87.html#B5http://www.nature.com/nphoton/journal/v4/n6/full/nphoton.2010.87.html#B5http://www.nature.com/nphoton/journal/v4/n6/full/nphoton.2010.87.html#B5


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CONTENTS:

1. INTRODUCTION2. ENTANGLEMENT3. TELEPORTATION

CLASSICAL TELEPORTATION QUANTUM TELEPORTATION

4. BELL STATE MEASUREMENT5. THE TELEPORTER6. EXPERIMENTAL ANALYSIS7. TELEPORTATION OF PHOTONS WITHOUT DESTRUCTION8. CAN THE ATOMS BE ENTANGLED TOO9. QUANTUM TELEPORTATION USED FOR SUPERLUMMINAL

COMMUNICATION

10. REAL EXPERIMENTS THAT DO TELEPORTATION11. HUMAN TELEPORTATION12. DECOHERENCE13. APPLICATIONS OF QUANTUM TELEPORTATION14. THINGS TO COMBAT15. CONCLUSION16. BIBLIOGRAPHY


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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 thatcomes 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 farapart 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 entangledparticles 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 theother 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 ofthe entangled entity, no matter where or how far away the entangled entity is located.


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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 ofa 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 thenreassembles 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 foundon the planet. Note that in either case the transporter needs to have complete informationon 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'sTheorem. 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 Correlationexperiments 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 abrave 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 smallerobjects 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.


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Classical teleportation

Let's start by assuming that the world is perfectly classical, that is, let's not worry aboutthe 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 cargoof 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 thereis 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 aretrying 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 twocopies 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 bepainful 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. Certainlya 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 Bwould be slightly different from the one that left A.


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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 willchange the state of a few atoms. Our goal should be that the errors that appear when weteleport 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.


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Quantum teleportationBut 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 input2. Transmits the results via the phone3. 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 mixedstrategy where we measure some positions and some momenta, however the uncertainty

principle basically guarantees that we will never obtain enough information to rebuildeven a modestly good copy of Jim. It appears that even before running Jim through theshredder, 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 andreconstruct" 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 oflight 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 haveLabs 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 relativelytrivial. 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.


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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 withsomething 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 extrarequirement 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 sendingone 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 firstentangled 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 createsome 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 nevermet 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 toLab 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 futuremany 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 havechosen 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. Thatis, 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


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(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., itsposition, 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 lightpolarization 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 thosedifferent 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 shallcall 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 israndom. However, if we measure its companionE2 photon with a polarizer oriented at 90

degrees relative to the first, then ifE1 passes its filterE2 will also pass its filter. Similarly

ifE1 does not pass its filter its companionE2 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, whichreflect 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.


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We direct one of the entangled photons, sayE1, to the

beam splitter.

Meanwhile, we prepare another photon with apolarization 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 bothE1 and Kreachthe beam splitter at the same time.

TheE1 photon incident from above will be reflectedby 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 bothphotons will end up going up and to the right as

shown.

Similarly, sometimes both photons will end up going

down and to the right.


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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 thephase shifts the light experiences when reflected,

the mixture of polarization states ofE1, and the consequent interference between the two

photons.

But sometimes one photon will end up going upwardsand 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 thephotons from the beam splitter: both upwards, bothdownwards, 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 otherdownwards occurs, perhaps surprisingly, 25% of the

time.


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The teleporter

Now we shall think about theE2 companion toE1.

25 percent of the time, the Bell-state measurementresulted in the circumstance shown, and in these cases

we have collapsed the state of theE1 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 thatthe companion to E1,E2, now has a polarization of

+450. Thus the state of the Kphoton has now been

transferred to theE2 photon. We have teleported the

information about the Kphoton toE2.

Although this collapse ofE2 into a 450

polarization

state occurs instantaneously, we haven't achievedteleportation 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 Kphoton.

Quantum entanglements such as exist between E1 andE2 in principle are independent of how far apart thetwo photons become. This has been experimentally

verified for distances as large as 10km. Thus, the

Quantum Teleportation is similarly independent of thedistance.

The Original State of the Teleported Photon MustBe 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 thephotons 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.


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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 twoangles. 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 3-dimensional 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 isdestroyed.

Until recently, teleportation was not taken seriously by scientists, because it was thought

to violate the uncertainty principle of quantum mechanics, which forbids any measuringor 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 moreit 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 copycannot 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 Einstein-

Podolsky-Rosen effect.


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In brief, they found a way to scan out part of the information from an object A, whichone 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 toC 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, sowhat has been achieved is teleportation, not replication.

As this figure suggests, the unscanned part of the information is conveyed from A to C byan 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 Abefore 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.


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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 individuallyrandombehaviorthat 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 informationabout 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 someraw 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 ofseveral treatments to be applied to object C, thereby putting C into an exact replica of the

former state of A.


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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 newlevel 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 non-

demolition (QND) measurement.after many years of experimental effort, researchers inFrance (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 avoidedwith 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 teleportationof 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 quantumparticle, 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 entanglementprocess for atoms, the researchers trap a pair of beryllium ions in a magnetic field. Theexperimental 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 teleportation be used for superluminal

communication?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.


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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, ourversion 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 forsuperluminal 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 quantummechanics 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 cannotconvey 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 roughly50 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 relatedproblem 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 ofpresent day experiments.


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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 wouldlikely 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. Thevisible 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. Thisinformation 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 hasposition 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.
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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 thisview 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 ofsomething 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 quantummechanics.

In principle, such a belief will have experimental consequences, as we should be able todetermine 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 veryhard 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. Whathappened 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 naggingquestion 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 whichunifies 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. Butwhen 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.


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Why not objects?

Teleportation of human body as a whole involves lots of complexities. And it may proveto 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 usefulways. 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 theenvironment (i.e., environmental noise) through stray interactions with the object.

Introduces a certain level of error in the exchange of quantum informationbetween the systems.

Fundamentally Limits q-Teleportation.

Applications of quantum teleportation

Quantum computer (computer that has data transmission rates many times fasterthan 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 originalwas involved in a mishap.)


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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 andaccurately 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).


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Bibliography

www.wikipedia.com

www.google.com

Quantum Teleportation Report

Documents

Transcript of Quantum Teleportation Report