The Runet has never experienced such a thirst for knowledge in quantum mechanics as after the publication in the Kommersant newspaper of an article mentioning plans to introduce “teleportation” in Russia. The program of the Agency for Strategic Initiatives (ASI) for the technological development of Russia, however, is not limited to “teleportation”, however, it was this term that attracted the attention of social networks and the media and became the reason for many jokes.

Then the entangled particles are separated to the required distance - so that photons A and B remain in one place, and C in the other. A fiber optic cable is run between the two points. Note that the maximum distance at which quantum teleportation was carried out is already more than 100 km.

The task is to transfer the quantum state of an unentangled particle A to particle C. To do this, scientists measure the quantum property of photons A and B. The results of the measurements are then turned into a binary code that tells about the differences between particles A and B.

This code is then transmitted over the traditional communication channel, an optical fiber, and the recipient of the message on the other end of the cable, who possesses the C particle, uses this information as an instruction or key to manipulate the C particle - in essence, restoring the C particle to the state that the C particle had. particle A. As a result, particle C copies the quantum state of particle A - the information is teleported.

What is all this for?

First of all, quantum teleportation is planned to be used in quantum communication and quantum cryptography technologies - the security of this type of communication looks attractive for both business and the state, and the use of quantum teleportation makes it possible to avoid information loss when photons move along an optical fiber.

For example, recently it became known about the successful transfer of quantum information between two Gazprombank offices in Moscow via a 30.6-kilometer fiber optic. The project, on which the Russian Quantum Center (RKC) worked, and in which Gazprombank and the Ministry of Education and Science of the Russian Federation invested 450 million rubles, actually turned out to be the first “city” quantum communication line in Russia.

Another direction ˜ is quantum computers, where entangled particles can be used as qubits – units of quantum information.

Another idea is the "quantum internet": an entire network of communications based solely on quantum communication. To implement this concept, however, researchers need to “learn how to transfer quantum states between objects of different physical nature - photons, atoms, quantum dots, superconducting circuits, and so on,” said Alexander Lvovsky, an employee of the RCC and a professor at the University of Calgary, in a conversation with the N + 1 publication. .

Note that at the moment scientists are teleporting in the ground states of photons and atoms; larger objects have not yet been teleported.

Quantum teleportation as "the same" teleportation

Apparently, hypothetically, quantum teleportation can still be used to create copies of large objects, including humans - after all, the body also consists of atoms, the quantum states of which can be teleported. However, at the present stage of technological development, this is considered impossible and is attributed to the realm of fantasy.

“We are made up of oxygen, hydrogen and carbon, with a little bit of other chemical elements. If we collect the required number of atoms of the necessary elements, and then, using teleportation, bring them into a state identical to their state in the body of the teleported person, we will get the same person. It will be physically indistinguishable from the original except for its position in space (after all, identical quantum particles are indistinguishable). Of course, I am exaggerating to the utmost - a whole eternity separates us from human teleportation. However, the essence of the issue is precisely this: identical quantum particles are found everywhere, but it is not at all easy to bring them into the desired quantum state, ”said Alexander Lvovsky in an interview with N + 1.

At a distance of about 1200 kilometers - between earth and space! The researchers also plan to conduct similar experiments on quantum teleportation between the Earth and the Moon.

Teleportation ... A word from science fiction books, from stories about space adventures, where heroes overcome gigantic distances in seconds using a teleporter. Quantum teleportation has nothing to do with the actual movement of objects. In that case, what is it and why is it called that? About quantum teleportation AiF.ru told the head of the laboratory of physics of the Polytechnic Museum Yuri Mikhailovsky:

“You need to understand that with quantum teleportation, there is no movement of an object from one place in space to another, as with teleportation in the usual sense of the word. With the help of quantum teleportation, it is not the object itself that teleports, that is, it instantly moves, but the state of this object! Roughly speaking, we have a certain object that has a certain state, and with the help of quantum teleportation we can transfer this state to another place so that an object with the same properties appears there. (In China, the state of particles between two points on Earth will be transmitted using a space satellite, which is going to be put into orbit for the sake of this experiment - ed.) But about the object - conditionally. Let me explain: now we do not know how to transfer the state of complex objects. It is about conveying the state of individual atoms or photons, nothing more.

In order to implement quantum teleportation, you need to create a quantum entangled pair. For simplicity, we will talk about one state, the state of the spin of the particle. It can be in two states: spin up and spin down. We will try to convey these states. So, we are trying to create a so-called quantum entangled pair (usually a pair of light photons). It is arranged in such a way that their total spin is zero. That is, one photon has a spin up, the other has a spin down, when we create this pair, their sum is zero. At the same time, not only do we not know where the photons are looking, but the photons themselves do not know in which direction their spins are directed. They are in the so-called mixed state, indefinite. Maybe spin up, maybe down, no one knows until the act of measurement is done.

But we have a guarantee that if we measure one spin and it looks up, then the spin of the other photon looks down. Now let's take two entangled photons and spread them over a long distance, a kilometer, for example. And here we take one of the photons and measure its state. We determine that it has a spin up, and at this moment, at a distance of one kilometer, the spin of another mixed photon turns into a state with a spin down. By the act of measuring one photon, we changed the state of another photon.

Usually these two entangled photons are called Ansila and Bob.

This effect of quantum entanglement is used for teleportation. We have a spin that we would like to teleport, it is usually called Alice. So, the total spin of Alice and Ansila is measured, and at this moment Bob receives the state of Alice, or conjugate to it (opposite). About which one, we learn from the result of the measurement. After that, we need to transfer this information through the usual communication channel. Should Bob be turned over or not.

If, for example, we transmit the states of 10 spins, then to complete the teleportation, it is necessary to send a message like: “Change to opposite states 1, 3, 5, 6 and 8”.

This is how quantum teleportation works.

A key study proving the fundamental possibility of quantum teleportation of photons.

This is necessary for the fundamental physical substantiation of the fundamental possibility of distant translation of genetic and metabolic information using polarized (spinning) photons. Evidence applicable to both in vitro (using a laser) and in vivo translation, i.e. in the biosystem itself between cells.

Experimental quantum teleportation

Quantum teleportation has been experimentally demonstrated - the transfer and restoration of the state of a quantum system at any arbitrary distance. In the process of teleportation, the primary photon is polarized, and this polarization is a remotely transmitted state. In this case, a pair of entangled photons is an object of measurement, in which the second photon of the entangled pair can be arbitrarily far from the initial one. Quantum teleportation will be a key element in quantum computing networks.

The dream of teleportation is the dream of being able to travel by simply appearing at some distance. The object of teleportation can be fully characterized by its properties by classical physics through measurements. In order to make a copy of this object at some distance, there is no need to transfer its parts or fragments there. All that is needed for such a transfer is the complete information about it taken from the object, which can be used to recreate the object. But how accurate does this information need to be in order to generate an exact copy of the original? What if these parts and fragments were represented by electrons, atoms and molecules? What will happen to their individual quantum properties, which, according to Heisenberg's uncertainty principle, cannot be measured with arbitrary precision?
Bennett et al. proved that it is possible to transfer the quantum state of one particle to another, i.e. the process of quantum teleportation, which does not ensure the transmission of any information about this state in the transmission process. This difficulty can be eliminated by using the principle of entanglement as a special property of quantum mechanics. It maps the correlations between quantum systems much more strictly than any classical correlations can do. The ability to transfer quantum information is one of the basic structures of wave quantum communication and quantum computing. Although there is rapid progress in the description of quantum information processing, the difficulties in controlling quantum systems do not allow adequate progress in the experimental implementation of new proposals. While not promising rapid advances in quantum cryptography (primary considerations for transferring secret data), we have previously only successfully proven the possibility of quantum dense coding as a way to quantum mechanically enhance data compression. The main reason for this slow experimental progress is that although there are methods for generating pairs of entangled photons, entangled states for atoms are just beginning to be studied and are no more possible than entangled states for two quanta.
Here we publish the first experimental verification of quantum teleportation. By creating pairs of entangled photons using a parametric down conversion process, and also by using two-photon interferometry to analyze the entanglement process, we can transfer the quantum properties (in our case, the polarization state) from one photon to another. The methods developed in this experiment will be of great importance both for research in the field of quantum communication and for future experiments on the fundamentals of quantum mechanics.

In June 2013, a group of physicists led by Eugene Polzik managed to conduct an experiment on the deterministic teleportation of the collective spin of 10 12 cesium atoms by half a meter. This work is featured on the cover. nature physics. Why this is a really important result, what the experimental difficulties were, and, finally, what “deterministic quantum teleportation” is, Eugene Polzik, a professor and a member of the executive committee of the Russian Quantum Center (RKC), told Lente.ru.

"Lenta.ru": What is "quantum teleportation"?

To understand how quantum teleportation differs from what we see, for example, in the Star Trek series, you need to understand one simple thing. Our world is arranged in such a way that if we want to know something about anything, then in the smallest details we will always make mistakes. If, for example, we take an ordinary atom, then it will not be possible to simultaneously measure the speed of movement and the position of electrons in it (this is what is called the Heisenberg uncertainty principle). That is, you cannot represent the result as a sequence of zeros and ones.

In quantum mechanics, however, it is appropriate to ask this question: even if the result cannot be written down, maybe it can still be sent? This process of sending information beyond the accuracy of classical measurements is called quantum teleportation.

When did quantum teleportation first appear?

Eugene Polzik, Professor of the Niels Bohr Institute, University of Copenhagen (Denmark), Member of the Executive Committee of the Russian Quantum Center

In 1993, six physicists - Bennett, Brossard and others - wrote in Physical Review Letters article (pdf), in which they came up with a wonderful terminology for quantum teleportation. Remarkable also because this terminology has had an extremely positive effect on the public ever since. In their work, the quantum information transfer protocol was described purely theoretically.

In 1997, the first quantum teleportation of photons was carried out (in fact, there were two experiments - the Zaillinger and De Martini groups; Zaillinger is simply quoted more). In their work, they teleported the polarization of photons - the direction of this polarization is a quantum quantity, that is, a quantity that takes on different values ​​with different probabilities. As it turned out, this value cannot be measured, but it can be teleported.

Here's something to consider: in the experiments of Zaillinger and De Martini, teleportation was probabilistic, that is, it worked with a certain probability of success. They managed to achieve a probability of at least 67 (2/3) percent - what in Russian is appropriate to call the classical limit.

The teleportation in question is called probabilistic. In 1998, we at Caltech did something called deterministic teleportation. We have teleported the phase and amplitude of the light pulse. They, as physicists say, like the speed and location of the electron, are "non-commuting variables", and therefore obey the already mentioned Heisenberg principle. That is, they do not allow simultaneous measurement.

An atom can be thought of as a small magnet. The direction of this magnet is the direction of the spin. You can control the orientation of such a “magnet” using a magnetic field and light. Photons - particles of light - also have a spin, which is also called polarization.

What is the difference between probabilistic and deterministic teleportation?

To explain it, first we need to talk a little more about teleportation. Imagine that at points A and B there are atoms, for convenience - one at a time. We want to teleport, say, the spin of an atom from A to B, that is, bring the atom at point B to the same quantum state as atom A. As I said, one classical communication channel is not enough for this, so two channels are required - one classical, another quantum. As a carrier of quantum information we have light quanta.

First, we pass light through atom B. An entanglement process occurs, as a result of which a connection is established between the light and the spin of the atom. When light arrives at A, we can assume that a quantum communication channel has been established between the two points. Light, passing through A, reads information from the atom and after that the light is caught by detectors. It is this moment that can be considered the moment of transmission of information through a quantum channel.

Now it remains to transfer the measurement result through the classical channel to B, so that, based on these data, some transformations are performed on the spin of the atom (for example, the magnetic field is changed). As a result, at point B, the atom receives the spin state of atom A. Teleportation is completed.

In reality, however, photons traveling through a quantum channel are lost (for example, if this channel is an ordinary optical fiber). The main difference between probabilistic and deterministic teleportation lies precisely in the attitude towards these losses. Probabilistic doesn't care how many are lost there - if at least one out of a million photons has reached, then it's good. In this sense, of course, it is more suitable for sending photons over long distances ( currently the record is 143 kilometers - approx. "Tapes.ru"). Deterministic teleportation, on the other hand, has a worse attitude to losses - generally speaking, the higher the losses, the worse the quality of teleportation, that is, at the receiving end of the wire, a not quite original quantum state is obtained - but it works every time, to put it bluntly, you press the button.

The entangled state of light and atoms is essentially an entangled state of their spins. If the spins of, say, an atom and a photon are entangled, then measurements of their parameters, as physicists say, are correlated. This means that, for example, if the measurement of the spin of a photon showed that it is directed upwards, then the spin of the atom will be directed downwards; if the spin of the photon turned out to be directed to the right, then the spin of the atom will be directed to the left, and so on. The trick is that before the measurement, neither the photon nor the atom has a definite direction of spin. How is it that, despite this, they are correlated? This is where the “head spin from quantum mechanics” should begin, as Niels Bohr said.

Eugene Polzik

And how do they differ in scope?

Probabilistic, as I said, is suitable for data transmission over long distances. Let's say, if in the future we want to build a quantum Internet, then we will need exactly this type of teleportation. As for the deterministic one, it can be useful for teleporting some processes.

Here we must immediately clarify: now there is no such clear-cut boundary between these two types of teleportation. For example, in the Russian Quantum Center (and not only in it), "hybrid" systems of quantum communications are being developed, where partly probabilistic and partly deterministic approaches are used.

In our work, the teleportation of the process was, you know, stroboscopic - we are not talking about continuous teleportation yet.

So it's a discrete process?

Yes. In fact, state teleportation, of course, can only happen once. One of the things that quantum mechanics forbids is the cloning of states. That is, if you teleported something, then you destroyed it.

Tell us about what your group has accomplished.

We had an ensemble of cesium atoms, and we teleported the collective spin of the system. Our gas was under the influence of a laser and a magnetic field, so the spins of the atoms were oriented approximately the same. An unprepared reader can imagine it like this - our team is a big magnetic needle.

The arrow has an indeterminacy of direction (this means that the spins are oriented "approximately" the same), the same Heisenberg one. It is impossible to accurately measure the direction of this uncertainty, but teleporting the position is quite possible. The magnitude of this uncertainty is one per square root of the number of atoms.

Here it is important to make a digression. My favorite system is a gas of atoms at room temperature. The problem with this system is this: at room temperature, quantum states quickly fall apart. In our case, however, these spin states live for a very long time. And this was achieved thanks to cooperation with scientists from St. Petersburg.

They developed coatings that are scientifically called alkene coatings. In fact, it is something very similar to paraffin. If you spray such a coating on the inside of a glass cell with gas, then the gas molecules fly (at a speed of 200 meters per second) and collide with the walls, but nothing happens to their spin. They can withstand about a million collisions. I have such a visual representation of this process: the cover is like a whole forest of vines, very large, and in order to spoil your back, you need to transfer your spin to someone. And there it is all so big and connected that there is no one to pass it on to, so he goes in there, flounders and flies back, and nothing happens to him. We started working with these coatings 10 years ago. Now they have been improved and proved that it is possible to work with them in the quantum field.

So, back to our cesium atoms. They were at room temperature (this is also good because alkene coatings do not withstand high temperatures, and in order to get gas, something usually needs to be evaporated, that is, heated).

You have teleported spin by half a meter. Is such a small distance a fundamental limitation?

Of course not. As I said, deterministic teleportation does not suffer losses, so our laser pulses went through open space - if we drove them back into the fiber, there would invariably be some kind of loss. Generally speaking, if you are engaged in futurism there, then it is quite possible to shoot at a satellite with the same beam, which will forward the signal to the right place.

You said that you have plans for continuous teleportation?

Yes. Only here continuity should be understood in several senses. On the one hand, we have 10 12 atoms in the work, so the discreteness of the direction of the collective spin is so tiny that it is possible to describe the spin by continuous variables. In this sense, our teleportation was continuous.

On the other hand, if the process changes in time, then we can talk about its continuity in time. So I can do the following. This process has, let's say, some kind of time constant - let's say it happens in milliseconds, and so I took it and broke it into microseconds, and the “boom” teleported after the first microsecond; then you have to return to the initial state.

Each such teleportation, of course, destroys the teleported state, however, the external excitation that this process causes does not touch. Therefore, in essence, we are teleporting a certain integral. We can "expand" this integral and learn something about external excitations. A theoretical paper in which all this is proposed has just appeared in Physical Review Letters.

In fact, such teleportation back and forth can be used for very deep things. I have something happening here, and something is happening here, and with the help of a teleportation channel I can simulate an interaction - as if these two spins, which have never interacted with each other, actually interact. That is such a quantum simulation.

And quantum simulation is what everyone is jumping at now. Instead of factoring into millions of digits, you can just simulate. Recall the same D-wave.

Can deterministic teleportation be used in quantum computers?

Maybe, but then it will be necessary to teleport the qubits. Here all sorts of error correction algorithms will already be required. And they are just beginning to be developed.

Professor of the Faculty of Physics at the University of Calgary (Canada), a member of the Canadian Institute for Higher Studies Alexander Lvovsky tried to explain in simple terms the principles of quantum teleportation and quantum cryptography.

Key to the castle

Cryptography is the art of communicating securely over an insecure channel. That is, you have a certain line that can be listened to, and you need to send a secret message over it that no one else can read.

Imagine that, say, if Alice and Bob have a so-called secret key, namely, a secret sequence of zeros and ones that no one else has, they can encrypt a message using this key, using the exclusive OR operation so that zero matches with zero, and one with one. Such an encrypted message can already be transmitted over an open channel. If someone intercepts it, it's okay, because no one can read it, except for Bob, who has a copy of the secret key.

In any cryptography, in any communication, the most expensive resource is a random sequence of zeros and ones, which is owned by only two communicating. But in most cases, public key cryptography is used. Let's say you buy something with a credit card in an online store using a secure HTTPS protocol. According to it, your computer is talking to some server with which it has never communicated before, and it did not have the opportunity to exchange a secret key with this server.

The mystery of this dialogue is provided by solving a complex mathematical problem, in particular, decomposition into prime factors. It is easy to multiply two prime numbers, but if the task is already given to find their product, to find two factors, then it is difficult. If the number is large enough, it will require many years of calculations from a conventional computer.

However, if this computer is not ordinary, but quantum, it will solve such a problem easily. When it is finally invented, the widely used method above will prove to be useless, which is expected to be disastrous for society.

If you remember, in the first Harry Potter book, the protagonist had to go through security to get to the Philosopher's Stone. There is something similar here: for those who have established protection, it will be easy to pass it. It was very difficult for Harry, but in the end he still overcame it.

This example illustrates public key cryptography very well. Anyone who doesn't know him is in principle able to decipher the messages, but it will be very difficult for him, and this will potentially take many years. Public-key cryptography does not provide absolute security.

quantum cryptography

All this explains the need for quantum cryptography. She gives us the best of both worlds. There is a one-time pad method, reliable, but, on the other hand, requiring an "expensive" secret key. In order for Alice to communicate with Bob, she must send him a courier with a suitcase full of discs containing such keys. He will gradually consume them, since each of them can only be used once. On the other hand, we have the public key method, which is "cheap" but does not provide absolute security.

Quantum cryptography, on the one hand, is “cheap”, it allows the secure transmission of a key over a channel that can be hacked into, and on the other hand, it guarantees secrecy due to the fundamental laws of physics. Its meaning is to encode information in the quantum state of individual photons.

In accordance with the postulates of quantum physics, the quantum state at the moment when it is attempted to be measured is destroyed and changed. Thus, if there is some spy on the line between Alice and Bob trying to eavesdrop or peep, he will inevitably change the state of the photons, the communicants will notice that the line is being tapped, stop communication and take action.

Unlike many other quantum technologies, quantum cryptography is commercial, not science fiction. Already, there are companies that produce servers connected to a conventional fiber optic line, through which you can communicate securely.

How a polarizing beam splitter works

Light is a transverse electromagnetic wave, oscillating not along, but across. This property is called polarization, and it is present even in individual photons. They can be used to encode information. For example, a horizontal photon is zero and a vertical photon is one (the same is true for photons with polarizations of plus 45 degrees and minus 45 degrees).

Alice encoded information in this way, and Bob needs to accept it. For this, a special device is used - a polarizing beam splitter, a cube consisting of two prisms glued together. It transmits a horizontally polarized stream and reflects a vertically polarized one, due to which information is decoded. If the horizontal photon is zero and the vertical photon is one, then one detector will click in the case of a logical zero, and the other in the case of a one.

But what happens if we send a diagonal photon? Then the famous quantum accident begins to play a role. It is impossible to say whether such a photon will pass or be reflected - it will do either one or the other with a 50 percent probability. Predicting his behavior is impossible in principle. Moreover, this property underlies commercial random number generators.

What to do if we have the task of distinguishing polarizations of plus 45 degrees and minus 45 degrees? It is necessary to rotate the beam splitter around the beam axis. Then the law of quantum randomness will operate for photons with horizontal and vertical polarizations. This property is fundamental. We cannot ask what polarization this photon has.

Principle of quantum cryptography

What is the idea behind quantum cryptography? Suppose Alice sends a photon to Bob, which she encodes either horizontally-vertically or diagonally. Bob also flips a coin, deciding randomly whether his basis will be horizontal-vertical or diagonal. If their encoding methods match, Bob will receive the data sent by Alice, if not, then some nonsense. They carry out this operation many thousands of times, and then “call up” over an open channel and tell each other in what bases they made the transfer - we can assume that this information is now available to anyone. Next, Bob and Alice will be able to weed out events in which the bases were different, and leave those in which they were the same (there will be about half of them).

Suppose some spy has wedged into the line who wants to eavesdrop on messages, but he also needs to measure information in some basis. Imagine that Alice and Bob have the same, but the spy does not. In a situation where the data was sent in a horizontal-vertical basis, and the eavesdropper measured the transmission in a diagonal one, he will receive a random value and forward some arbitrary photon to Bob, since he does not know what it should be. Thus, his interference will be noticed.

The biggest problem in quantum cryptography is loss. Even the best and most modern fiber gives 50 percent loss for every 10-12 kilometers of cable. Let's say we send our secret key from Moscow to St. Petersburg - for 750 kilometers, and only one out of a billion billion photons will reach the goal. All this makes the technology completely impractical. That is why modern quantum cryptography only works at a distance of about 100 kilometers. Theoretically, it is known how to solve this problem - with the help of quantum repeaters, but their implementation requires quantum teleportation.

quantum entanglement

The scientific definition of quantum entanglement is a delocalized state of superposition. Sounds complicated, but a simple example can be given. Suppose we have two photons: horizontal and vertical, whose quantum states are interdependent. We send one of them to Alice, and the other to Bob, who make measurements on a polarizing beam splitter.

When these measurements are made in the usual horizontal-vertical basis, it is clear that the result will be correlated. If Alice noticed a horizontal photon, then the second one, of course, will be vertical, and vice versa. This can be imagined in a simpler way: we have a blue and a red ball, we seal each of them in an envelope without looking and send it to two recipients - if one receives red, the second will definitely receive blue.

But in the case of quantum entanglement, the matter is not limited to this. This correlation takes place not only in the horizontal-vertical basis, but also in any other. For example, if Alice and Bob rotate their beamsplitters 45 degrees at the same time, they will again have a perfect match.

This is a very strange quantum phenomenon. Let's say Alice somehow turned her beam splitter and found some photon with polarization α that passed through it. If Bob measures his photon in the same basis, he will find a polarization of 90 degrees +α.

So, at the beginning we have a state of entanglement: Alice's photon is completely undefined and Bob's photon is completely undefined. When Alice measured her photon, found some value, now we know exactly which photon Bob has, no matter how far away he is. This effect has been repeatedly confirmed by experiments, this is not a fantasy.

Suppose Alice has a certain photon with polarization α, which she does not yet know, that is, in an unknown state. There is no direct channel between her and Bob. If there was a channel, then Alice would be able to register the state of the photon and convey this information to Bob. But it is impossible to know the quantum state in one measurement, so this method is not suitable. However, between Alice and Bob there is a pre-prepared entangled pair of photons. Due to this, it is possible to make Bob's photon take the initial state of Alice's photon, "phoned" later on a conditional telephone line.

Here is a classic (albeit a very distant analogue) of all this. Alice and Bob each receive a red or blue balloon in an envelope. Alice wants to send Bob information about what she has. To do this, she needs, having “phoned” Bob, compare the balls, telling him “I have the same one” or “We have different ones”. If someone eavesdrops on this line, it will not help him to recognize their color.

Thus, there are four options for the outcome of events (conditionally, the recipients have blue balloons, red balloons, red and blue, or blue and red). They are interesting because they form a basis. If we have two photons with unknown polarization, then we can “ask them a question” in which of these states they are, and get an answer. But if at least one of them is entangled with some other photon, then the effect of remote preparation will occur, and the third, remote photon will “prepare” in a certain state. This is what quantum teleportation is based on.

How does it all work? We have an entangled state and a photon that we want to teleport. Alice must make an appropriate measurement of the original teleported photon and ask what state the other one is in. Randomly, she receives one of four possible answers. As a result of the remote cooking effect, it turns out that after this measurement, depending on the result, Bob's photon went into a certain state. Prior to that, he was entangled with Alice's photon, being in an indefinite state.

Alice tells Bob by phone what her measurement was. If its result, let's say, turned out to be ψ-, then Bob knows that his photon has automatically transformed into this state. If Alice reported that her measurement gave the result ψ+, then Bob's photon took on the -α polarization. At the end of the teleportation experiment, Bob has a copy of Alice's original photon, and her photon and information about it are destroyed in the process.

teleportation technology

Now we are able to teleport the polarization of photons and some states of atoms. But when they write, they say, scientists have learned how to teleport atoms - this is a deception, because atoms have a lot of quantum states, an infinite set. At best, we figured out how to teleport a couple of them.

My favorite question is when will human teleportation take place? The answer is never. Let's say we have Captain Picard from the Star Trek series who needs to be teleported to the surface of the planet from a ship. To do this, as we already know, we need to make a couple more of the same Picards, bring them into a confused state that includes all of his possible states (sober, drunk, sleeping, smoking - absolutely everything) and take measurements on both. It is clear how difficult and unrealistic this is.

Quantum teleportation is an interesting but laboratory phenomenon. Things will not come to the teleportation of living beings (at least in the near future). However, it can be used in practice to create quantum repeaters for transmitting information over long distances.