Anton Zeilinger - Quantenverschränkung und Quantenkommunikation

On the roofs of Vienna is the ground station for one of the most exciting experiments of today. From here physicists test quantum communication in the universe. The Bern Quantum Space Test is the technical name for this station. Together with a satellite, secret messages are supposed to be transmitted between space and Earth. Transmit quantum entanglement over a distance of thousands of kilometers. Of course, it's all based on the entanglement of these photons and therefore this spooky long-distance effect. It is then resolved locally during the measurement into a defined state, which we then write with a data stamp.

With a data stamp timestamps can be provided and then compared to the transmitters data and the key can be generated. The station is now a transmitter. From here photons, the smallest particles of light, are sent to the Leopoldsberg church on the outskirts of Vienna, and from there the experiments that form the basis of a completely new data encryption called quantum cryptography are reflected. It is possible to encrypt things in such a way that not even a CD or a well-equipped institution, no matter how large, can remove them. Quantum physicists at the Austrian Academy of Sciences and researchers at the Austrian Academy of Sciences are already very close to this goal.

Academy of Sciences In China they will be able to carry out quantum physics experiments in space and transmit data absolutely securely. Scientists will check how the connection between the ground station and the reflectors works here in Leopoldsberg. The challenge of the task is how to communicate in space. The light quanta sent to Leopoldsberg will be reflected there with the help of mirrors and recorded again in a small telescope here at the ground station. If it works here, it will work in space too. satellite, researchers are convinced of the ceiling quantum information here an optical link has been installed about six kilometers (6 km approximately) The effective thickness of the Earth's atmosphere, that is, the Earth's atmosphere, becomes much thinner upwards if it were not like that, but in reality the same density would be maintained even if there are only six kilometers.

The experiments we are doing here in Vienna on rooftops are certainly representative. For a quantum optics connection between a satellite in Earth orbit and an atmospheric ground station. The disturbances, the absorption, all these problems that arise here are practically equivalent and quite significant, so here we have structures with which we can characterize the atmospheric disturbances and measure them. Then we evaluate that from y and we can conclude whether a link exists. from a satellite to a ground station is also realistic Albert Einstein, together with his colleague Boris Podolski and Nathan Rosen, discovered in 1935 something apparently crazy and completely absurd: the entanglement phenomenon that the Austrian physicist Erwin Schrödinger describes as characteristic.

Property of quantum mechanics: two particles, for example light particles, are closely connected to each other at any distance, as if by magic at great distances, so that measurements of one of the two immediately change the state of the other without there being a signal from A to B and of course you say to yourself how is that possible and you have to say that quantum physics can describe this mathematically wonderfully, that is not at all. There is no doubt what is correct, but clearly understanding that is the challenge and you haven't done it. Actually, it hasn't been resolved yet.

However, quantum physics has been demonstrated thousands of times in experiments. Now scientists also want to use the space as a laboratory. On board a Chinese satellite there will be a source of entangled photons. Communication with single photons is established between satellites and Earth, allowing intercontinental data exchange that is interception-proof. In this satellite project that we are carrying out together with the Chinese Academy of Sciences, the objective is to create a source of entangled photons in satellites. Then they can send the two particles to two different points on Earth and then they can show this spooky long-distance effect at much greater distances, first of all, which exists where it would be a new result because this was done again. distances of 1000, a few thousand kilometers not yet tested and, secondly, it can be used, it can be used, for example, by sending secret things.

With the help of the phenomenon of long-distance spooky effects, messages can be sent from outer space. in encrypted form An unbeatable cult, which is protected against illegal eavesdropping by a law of nature. This encryption technology, so-called quantum cryptography, is considered the most developed application of entanglement to date in information technology. Secret password. A practical application of a phenomenon that has not yet been fully understood. It is comparable to the situation of a dice when a dice is rolled on one side and shows the random time between 1 and 6 when a dice is rolled on the other side. for bob we say, for example, that the first die lets the second die explode, so bob now throws and rolls his, which is also a die, also at random in a result, at random, a number between one and six, they both have random results and it's not surprising that there's nothing exciting about it if you put together the results of the measurements, but if you always roll the dice at the same time, we can, and that's one of those sources, produce the dice that are produced with each throw.

Individually showing random events, but together they always show the same number of eyes, that means All I know about this pair of dice systems is that they have properties in common. They always show the same two eyes, but no single one. That's still random in classical physics, it's impossible for every coin to have two sides; a quantum mechanical coin would have all the positions. at the same time and only the measurement is determined by the state in which a coin randomly lands on heads or tails, meaning that in half of the cases they will simply have the same side up and in the other half of the cases they will have sides different in the above, this is called classical correlation, it is so good that we see it in everyday life or in the lottery, it is somewhat complicated, but in reality it is apparently possible with such an experimental setup two dice two coins or Dice is a better example because it can even be taken but it can be communicated two dice always show the same number of eyes without exception this cannot be reconciled with our everyday understanding of physics how are entangled photons generated?

An ultraviolet laser beam is projected onto a non-linear crystal when focused, one photon decays into two new photons, which may be entangled in their polarization, that is, in vibration. These two photons are transferred via glass fiber to so-called detection units and analyzed in the computer. These two photons have the same frequency and the same polarization. so it doesn't matter if I have a polarization on one side, I will measure the same polarization on the other side and that is now the miracle of quantum mechanics that it now works with any polarization. I can set any linear polarization and still have the other. photo the second photo has the same polarization and that's what's crazy, these two photons spill over into the polarizing beam tyler the photons that have now come out of this dispute, I no longer have any information about the direction in which. were punched and generated periodically on my nonlinear crystal.

So I don't have any information about what polarization individual photons carry. The only thing I can determine through measurement is what you can see here. Through measurement I can determine at what polarization I want to measure a photo and I see it standing still, that's what you call a constantly creepy effect at a distance, that the other photo has the same polarization. Experiments have shown that this remains up to a distance of 150 kilometers these photons retain their indistinguishability and their entanglement at incredibly large distances at distances not developed for quantum mechanics. Quantum mechanics was developed for scales of atoms and long photons.

In fact, back then we wanted to understand how atoms and photons work. we interact with each other behind them. We use these same similar structures. At the time, the ideas were called experiments because they were so crazy, but we can actually build these things today in the lab, which is a great technique. effort individual photons are very small units of energy, we can measure it today and demonstrate it at very large distances. This is reminiscent of a scene from the famous movie The Third Man, a British thriller from 1949, because basically the quantum physicists set up their laboratory in the sewage system. from the city of Vienna in 2004.

They managed to teleport photons here at a distance of 600 meters across the Danube from station A, physicists call it all, they transmit the oscillation state of one of the two photons. in a photon 600 meters away at station b, called bop for short, without the light particles coming into contact with each other, if you listen or watch on the intermediate channel, the information transmitted is not in the quantum channel nor in the channel that is the source. With Bob logging in, the full information is still available on the classic channel. There is no complete information about the club beat that wants to be broadcast on any of the channels.

The first thing that's interesting, the second thing is about quantum delegation. The interesting thing is that in conventional communication methods I always have particles whose properties I change in such a way that I basically speak my polarization in charge, whatever the phase of the light, whatever it is. Learn about the coding mechanisms of quantum teleportation on the Internet. If the system is not the case, it is only imposed afterwards. It is actually a creepy action without a distance as mentioned. In reality, information is transmitted without having one. direct line Entanglement is conveyed first and here we know that entanglement is not an individual property of a photon but rather a sum of two properties of two photons or more.

There may be many more particles. a distance of more than 140 kilometers, as demonstrated by bee physicists. An important point is that entanglement has been experimentally tested x times and not even at large distances and that not only means it exists but they said I can't use it. The only thing missing is a clear explanation. Viennese quantum physicists are creating quantum information over great distances for the first time. In the specific case, between the Canary Islands of La Palma and Tenerife, a record distance of 144 kilometers in space. , two photons remain connected to each other at this large distance and can be used for the transmission of quantum information.

As a next step, researchers are trying to transfer quantum information between Earth and a satellite installation in space. The question now is yes. You can use these technologies that were actually developed to enable classic high-speed data rates to any point on Earth. You can also use these optical structures for these sources. We have many theoretical studies in our institute. Practical studies have also been carried out. this, among other things, on a link between La Palma Tenerife, where you have approximately the same attenuation where the photons are transferred from one island to another and you can approximately see the atmospheric disturbances and you can also approximately see the losses on a link satellite.

In fact, a satellite with a source of entangled photons will be launched in the near future. An encryption method such as intercontinental quantum cryptography may be used. The essence of quantum cryptography is that I can generate a key from these entangled light particles. with the transmitter So the receiver cannot block it, it can decrypt it and the important thing now is that if someone tries to spy on this connection through which the key is created, it will be discovered immediately not subject to a measurement without changes its state and I see this change immediately depending on the need, quantum keys cannot be sent to users another big advantage these keys can be recreated again and again for the respective purpose the sequence is due to absolutely random natural laws secreted for a long time disturbing system andTherefore , are detected immediately and the satellite simultaneously illuminates what they see in the area between Vienna and Graz, which means that anyone who sets up a telescope in the space between them can also record and evaluate these photons.

It is not possible to decode our data. Our key to global data transmission appears to be within reach with the help of satellites. We want to do experiments here at our institute where we do space-to-ground links where we really can. transmit entangled photons from space to the ground and this would allow us to create a cryptographic key, which would allow global quantum communication to be established. In cooperation with the Academyof Sciences of China, we were able to establish a collaboration in which a Chinese. The satellite would generate these individual photons in a very similar way on the satellite to transmit them to Earth and we here in Austria and other places in Graz in Austria in Styria receive these photons, measure them and create a quantum cryptography key which is then symmetric at the end of this procedure to a key created in China, which is the secret of quantum physics: it will be able to do it at such great distances and this will allow, for the first time in the history of humanity, theoretical access to information.

Secure communication method over an intercontinental distance between Graz and, in this case, the ground station located near Beijing. Quantum cryptography naturally arouses great interest in many groups, banks, governments and, not least, the military. The US Department of Defense supports quantum technology. American physicists in this work, however, until now quantum physics encryption technology has barely been used by governments. The technology has been selected on several occasions for demonstration purposes. We have made or made a bank transfer in Vienna. Other applications have already been made with a little effort, but there is no truly routine technical application yet because there are still two challenges to overcome.

One is the distance factor sg, so far only at distances of 10.-20 kilometers, i.e. the size of a city for example, and the second is the data speed, the data speed is too low in comparison with what the Internet is in general. I hope this is a technical development issue. Taking a lot of territory and Developing better methods will probably fix the fact that our understanding of the world has changed radically because of quantum physics. Categories like space and time seem to fail. However, quantum theory is an integral part of our daily lives. In fact, it is also the most economically successful theory, because semiconductor chips, for example laser magnetism, none of this would exist without quantum physics, which all modern high technology, including the television through which people now watch This movie does not exist in today's modern world.

Inconceivable without quantum physics, MRI is a prime example of a beneficial technological application: Quantum physics enables great inventions, but ultimately its concepts and methods are not fully understood. Where's the problem is that quantum physics makes some predictions? and you have some phenomena that are based on intuition or, let's say, common sense, they contradict the entangled quanta and they contradict the classical world because their properties are not clearly defined before a measurement and after the measurement they are much more closely connected and much more more correlated than could be explained by a classical interaction, quantum mechanics now provides this question with a complete description of physical reality.

The debate between Albert Einstein and Niels Bohr, unlike Bohr, rejects the claim that particles can be in several places at the same time as long as they are not observed. Throughout their lives, there are paradoxes that have been resolved today, for example. certain things are already understood, for example that you can only talk about the properties of the system if you have actually observed and measured it and. there are no other properties because they are, for example, one of the things that are obtained from quantum mechanics, with which, however, it is already an interpretation, and Albert Einstein's Copenhagen interpretation has developed almost all the problems and important thought experiments.

On quantum mechanics he attempts to conceptually explore the depths of quantum theory and begins to develop completely new concepts to understand it. However, in relation to particle entanglement, he talks about a spooky long-distance effect and is a supporter of it. classical world view called locally realist on board the issue is the moon, no one looks at it either, but for very good reasons because he really understood what it was about under constant outside the point he was wrong today and would re-give Einstein's opinion on the current situation knowing that it is certainly It is not as simple as saying that it is very, but rather saying with certainty how the quantum behaves.

It is not possible to understand the behavior of entangled systems if we start from certain reasonable assumptions about how quantum systems behave. The world should be. That was the great discovery of the Irish musician John Bell. He throws the classical worldview on the pile, which just shows mountains when I have these entangled particles and I make one measurement here that influences the other. explain it by the fact that they somehow have properties that they have. I can use it and produce measurement results and it soon says no, that's not possible, but it can only be used as a book on long distance effects.

Here he agreed with the form. and this is not only philosophically important, but the so-called Bavarian unequals did not say anything more than if the property was then known that the two particles are connected as strongly as they are according to quantum mechanics, but weaker, i.e. This is now the practical meaning today, this is a method to check how well the device works when it is very close to the equation, the seriously injured have a wonderful pivot and that means that is also important in police graffiti if we are okay if my particles are depression against those who have already been injured can use them for cryptography and can be sure that a citizen has no chance of hearing it until in the late 80s, scientists see the entanglement of two particles that Anton Zeilinger discovers with his colleague Green Bürger and Horn. the entanglement of three particles the so-called Grünberger state Horn Zeilinger who says that measurements on two particles cannot determine the state of the third particle For me, personally, the most important experiment that has taken ten years to become possible is the realization of these three particles particle rotations, that's why it was so difficult and challenging that sometimes we said that there is something that works, then testing it it doesn't, maybe it doesn't even exist.

It didn't take long until they found a way to see that and today this This is something natural, but at that time this was a whole story, something that no one suspected then. Entanglements of three or more particles, called GHz states after their discoverers, represent an important prerequisite today. The development of quantum computers are experiments that clearly confirm the prediction of quantum mechanics. Why are you convinced of a prediction? Because in the event that you had incredibly consistent predictions, everything fit together, everything was mathematically beautiful, it was very simple, and it turned out well. a few lines prove it and we physicists believe that if something simple mathematical is really wood, the content is strangely similar, it is often like this in physics, the Viennese quantum physicists can prove almost a hundred years after the discovery of the new physical theory that In the quantum world the concept of information is of fundamental importance, future applications such as intercontinental quantum cryptography will demonstrate that how big is the quantum world?

The laws of quantum physics only apply to small particles. Therefore, quantum physics has no limits. It should also apply to macroscopic objects. This is not the case. A very big challenge to show quantum phenomena for macroscopic effects for the simple reason that when a system interacts with the environment it loses its quantum state because information is released into the environment, which means that. that as a system it has to isolate itself very well from the environment and this to see phenomena and of course it is more difficult with a large apple than with a single atom, for example, but for me that is basically a technical challenge, not a question of principle. : there is no transition between the micro and macro world.

This is ultimately the driving force of this experiment, which examines quantum effects and entanglement on the macroscopic scale. The focus is on the spatial structure of light and quantum. Macroscopic wildcard systems in our city at scale. Quantum effects only appear in principle in individual photographs of Ranzel particles or in our world very few of the same quantum effects are seen, in our world there are no magnitudes of 10 to the power of a. 23 particles this is what the effects look like net.de smear what we are trying to do here is take the effects exactly in the direction macroscopically maybe to understand them better maybe to have an intuitive picture of them Maybe to see new effects what happens when properties can enter the macroscopic world With the help of a computer program, the structure of liquid crystals can be changed in the experimental setup This has a direct effect on the incident light Changing phase information is obtained, for example through a rotation What we are doing is changing the structure of the light.

We are doing this with a laser. You can drive a laser. You can see it here and there. It's on a device that can perform holographic transformations. crystals You see a liquid crystal display and you can control the liquid crystals it works electrically with a computer that programs the cameras as well as an HD screen and gives the liquid crystals information about how the light should change and if you now have certain information. on the screen about the liquid crystals I am asked accordingly the structure of not changing that appears here and that is the reason why the cornerstone of our experiments, how we continue here, physicists test the magnitude of entanglement in particles of light that they spin rapidly, a world record is achieved, they generate the largest quantum numbers to date, there is a possibility that light has particularly strong impulses, high angular momentum quanta in the open form and then you can say okay and, in In principle, you can theoretically become as strong as you want to be able to give. such a strong angular momentum to a light particle that if you send it often to your hand, for example, I will make a very small example.

Then you will notice with your hand in which direction your hand would start to kick and even though it does not have a strong angular momentum it could still be entangled with another part with light particles it could be entangled with the other light particle in this angular momentum no like polarization here but angular momentum and that is, so to speak, a way of generating macroscopic values, that is, rotational impulses so strong that you can feel canyons, super sensitive cameras or direction possibilities and still have these strange properties of quantum physics, such as entanglement. That's a possibility, it's more of a fundamental approach, but in the experiment we did with this By training high angular momentum quanta pulses or strong pulses, we were able to show that you can also improve angular resolution particularly strongly.

With angle measurements with a few photons you can measure angles very precisely, which we have an application or transfer the momentum to other objects where, for example, you can only send a few light particles to them and still transmit a strong angular momentum, so that we just wanted to show that even though you're only working with individual light particles, the angular momentum can get very, very strong. And we were able to scale it up to two orders of magnitude as was possible until now. Since Einstein's ghost can be seen in real time, for the first time in the history of science it is possible to capture the quantum phenomenon on film.

How a measurement on a particle of light affects a particle scattered by it. A large number of photons create these complex spatial patterns. To clarify everything, we were able to do it for the first time. using the camera very quickly you can turn it on and off and then we use the camera to capture these three impulses when a light has an angular momentum so it has a very special spatial structure so it is also a ring mode or at different points and we were able to measure that with this camera. What we did was convert one photon and measure the polarization of the photon into the other and I had this measurement at the same time. at the same time it gave a signal to turn the camera on or off and then the photographs that we also took with the camera, so basically every time we measure police actions there you can get a signal.

He looked at it and then saw this exact photo. There is a white dot somewhere in the black camera image, but we often do that and add it together and see this spatial structure there. You can't see much entanglement yet. The exciting thing was that we were able to do it so quickly. that we use the polarizer to measure it. We were able to change the other photon that we didn't cross at all, so it rotated the polar gate and at the same time the structure here also changed, so basically you had the ones that I was able to see the entanglement, the effect of live entanglements, see that it had that be what is believed incamera depends on exactly how the associated particles are measured, so far this entanglement of angular momentum quanta has been shown before, but only in a very small area, i.e. 23 momentum quanta per photon.

We were able to use this trick to achieve polarization entanglement and then pulse conversion occurred. We were able to expand it to 303 momentum quanta per photo, which is now 300. Ask is a big number, it is by far the largest that has been measured so far, as far as we know. The entanglements with such large numbers. Rotating with such large quantum numbers is not that easy to do. On the other hand, if he said. For example, with the rotating hand, the value is still too small for one to really feel something in the hand. We still have many more steps to take.

Many people hope that quantum physics will spark a computing revolution and new software applications. In theory, quantum computers could be millions of times faster than conventional computers. Quantum teleportation is the ideal means of transferring information between potential quantum computers. The information is not presented with humor, but with quantum bits in so-called cubes. They can't just be zero or one. but one and zero at the same time, therefore complex information could be stored in the overlay. Recently there have been interesting advances in a universal quantum computer that could solve any problem like a universal computer does. We think it's probably smart to build special quantum computers that simulate certain problems, like solid state physics problems, how a solid is structured, how it works, which again is important for all of semiconductor technology and everything out there. t, for example, and nanotechnology is exactly the same thing and that's where it looks like it's probably going to be relatively interesting over a ten year period, say, for systems that can do something that an older computer can't do yet for quantum universal. computer, we will probably have to wait even longer, but again it could be that 23 young students or postdocs suddenly came up with a great idea and everything is working.

Many research groups around the world are working on creating supercomputers. New quantum processors will be used and perhaps a global quantum Internet based on teleportation can soon be created. Viennese quantum communication researchers can generate quantum information using entangled photons transmitted over long distances, which they have proven time and again to be the resource for producing quantum technology. mechanical entanglement and generating it over long distances that is our domain we have shown that it is technically feasible a global Internet is technologically in the area of ​​additional relativity and quantum which is one of the previously unsolved problems of physics the laws of the theory general relativity determines the movement of the planets in the solar system as well as the development of the entire universe the second pillar of modern physics is quantum theory is the basis of the atom of elementary particles and solid state physics but both theories together the theory of relativity and quantum theory are not compatible Today we do not know how to combine these two theories and here experiments are necessary experiments are necessary as was the case at a time when quantum physics was discovered was invented was invented by his parents his spiritual parents when there were experiments that were no longer available they could explain the same applies to the theory of relativity then the experiments of thousands & more di experiments where they wanted to measure the speed of the earth in meters and they did not find this effect .

In fact, experimental data emerged that were no longer available in standard theory at that time. The classical theory and, interestingly, in a very similar era, these two theories are incredibly inconceivable for our current technological society. The theory of relativity arose without which. Satellite navigation would be a strange word for us and quantum physics, and computers are becoming a strange word for us today. These two theories are very important, very successful, very efficient but not incompatible and I consider that to be the most interesting area of ​​research. ​​The future to see where the problems are here, where the effects occur and in what theory?

That seems to me to be one of the most dominant and burning questions in physics. In the present, the reality of the quantum, although it may be. It can be beautifully described mathematically, almost a hundred years after the establishment of quantum mechanics, it still cannot be fully understood. Visual understanding is not something we like, but perhaps it can still be understood and that is the challenge: why is the world so strange? These phenomena exist and it is also a question of remuneration, it is just a conjecture that is also discussed, that our usual idea of ​​space and time is not entirely correct, so that two places that we believe are separated in a deep philosophical relationship.

The meaning may not be separated, but space is a construction that will allow us to describe the world. Our world is a quantum world and quantum physics is a wonderful description of nature, but it will also continue to develop, experiments are ongoing.