 When you look at the history of quantum physics, it's gone through a number of revolutions. When I was a graduate student in the dark ages, people were still kind of worried about the foundational issues, but at a very fundamental mathematical level. And people thought of experiments which are sort of thought-based, Gdankin experiments to try and illustrate some of the fundamental behavior of quantum matter. Anton Zalinger is the person who actually carries these things out, as we'll hear. I've known Anton for a very long time. A number of episodes, which I will recount to anybody later on during the drinks, you must ask him about the Dalai Lama's visit to his laboratory at some point. But in particular, when Slovakia joined the European Union, we'd had an agreement that we would do all sorts of things to celebrate that. And a group from Vienna, and a group from Slovakia, decided that they would send a greeting from one part of the border to the other to celebrate the accession of Slovakia. And a group from Vienna sent off this quantum key distribution, quantum cryptographic graphic message, and it decoded at the other end. And I'm aware that we have diplomats present, and the message essentially from the Viennese side to the Bratislava side said, welcome back. Those of you who know anything about the Austro-Hungarian Empire will realize. Anton has distinguished himself for a wide variety of experiments, initially with neutrons, and then with highly correlated beams of light at the quantum mechanical level, often using parametric down conversion. His famous experiment in the end of the 90s on quantum teleportation was a landmark within the field. He's gone on to work on ways in which information can be carried quantum mechanically. Famous third man experiment of key exchange involving the sewers of Vienna. Lots of things we can relay to you at another time. When the Institute of Physics looks back on its growth, we now got what, 34,000 members. And with members from all over the world, it was really very fitting that we had an international award, a premier award to recognize excellence in the physical sciences. And I think it's really fitting that our first awardee of the Newton Medal, our international medal, is Anton Zylinger, a citizen of the world, one with whom the UK quantum optics community have enjoyed a very happy and very long relationship. So we all look forward to hearing Anton's lecture as the first Newton lecture of the IOP. So Anton, welcome. Thank you very much, Peter, for your kind introduction and for the precise memory concerning the, what I call the Slovakia event where we were in the car together, actually, crossing the border. Serviette Frau Bočaftarin, the president of the Institute of Physics, my dear colleagues. I am really very grateful for having been chosen for some reason, which is strange to me, the first recipient of the Newton Medal. This is quite a distinction. I highly appreciate that. So today I have been told to give the first Newton lecture, and I chose the title Quantum Information and the Foundations of Quantum Mechanics. This is a title which would have been impossible the years ago when I started to be interested in the foundations of quantum mechanics. What you see here in the picture is a telescope. It's a telescope on one of the Canary Islands, on the island of Tenerife, and I will mention more about this kind of experience later on. Let us go back a little bit to the beginning of quantum mechanics. The birth of quantum physics is often said to be the year 1900 when Max Planck explained the black body radiation as an assumption of the quantum of light, of the quantum of action. I recently discovered that this dating might be incorrect. Actually, one and a half years before, Max Planck had a quantum of action written down in a paper. At that time he did not appreciate its importance, but in 1900 he also did not appreciate its importance. So the foundation of quantum mechanics might argue that it started actually in June 1899. I wrote down four names here who are not often mentioned, Kurlbaum, Luma and Bringsheim and Rubens. These were the people who actually did the experiments on black body radiation. You see a picture which this is a recreation of the experiments back then. The black body investigated this here. So this is a hollow cylinder which can be heated from the outside and one side is the light coming out here. And to explain that light, Max Planck had to assume that light is quantized, that it comes in divisible quanta. I want to jump right into the matter of my talk. In a sense, early quantum physics was signified by the fact that many of the interesting things people predicted they could not do at that time because of technological problems, technological limitations. And the two fathers of quantum physics, Heisenberg and Schrodinger, had their part in predicting some of these phenomena using Gedanken experiments, using thought experiments. Here is Heisenberg's microscope of 1928 where he shows that you cannot measure the position of an electron without changing its state by a reflection of photons. And back here is Schrodinger's famous cat paradox where he couples the states of a cat, from a dead to a radioactive atom. The radioactive atom can, after some time, be in a superposition of decayed and not decayed, and therefore, if quantum mechanics is universally valid, the cat is also in a superposition of dead in the life, which clearly doesn't make any sense. And there are scores of papers where people argue why it doesn't make sense to talk about cats being in a superposition of dead in the life. The way we read such papers where people in general propose some limits for the validity of the laws of quantum mechanics, the way we read them is simply to find out that while the papers are certainly correct, what's the way around? What is the experimental way around the argument? I will mention a little more in that direction. The next step in Gedanken experiments was the famous Bohr-Einstein dialogue in the late 20s and early 30s. Here's a picture from the dialogue, the two-slate experiment. This picture was made by Niels Bohr himself in the write-up of 1948. The dialogue was essentially, philosophers might forgive me for making this statement so short, was essentially that Einstein's position was that physics is about what is, about reality out there, while Bohr's position was that physics is about what can be said about the world. And I will come back to this dichotomy a couple of times during my talk. This drawing was made by Bohr, and I really like it. Bohr was a theoretician, as you know, but you see he threw the screws here. So he knew that details in experiments are very important. I don't want to go into too much details. The question raised by Einstein is you can do this experiment which is easily understood with intensive light. You get dark and bright fringes. You can do this experiment with individual photons, and then the obvious question is, what happens? It turns out that with individual particles you will get also the stripes, and furthermore, you then can raise the question which Einstein did was which of the two slits does a particular particle go through, and if it goes through, say here, how does it know whether the other one is open or not, because it has to know that to show the interference pattern. The modern way, and Bohr's answer was to say that you are only allowed to talk about features of the world like a path taken if you really do the experiment which allows you to determine what happens. A further jump from Bohr into the beginning of some of these fundamental experiments. This is 1975, experiments done by my supervisor in Vienna, Helmut Rauch, who started the field of neutron interferometry. You have this kind of devices made of perfect crystals, the size here is a few centimeters, and you split an incoming beam of neutrons onto different trajectories and bring them on superposition again. This kind of experiment is now everyday fare with atoms and molecules and so on, but back then it was quite unique. I have a feeling that in terms of enclosed area, this is still the record for interferometers probably. So these first experiments were done in Vienna actually in 1974, 1975, and here's one example of one of these early experiments. It's what's called the spin rotation of a neutron. The simple point is that if I stand here and if I turn around once, then the universe is the same again. Not much change. Not if I wear a quantum object, if I wear a quantum object, then I have to turn around twice to have the same universe again, and here the interference fringe is seen in this kind of experiment. The important point in terms of intensity here is that the intensity in this experiment is so low that when you detect one neutron, this next neutron which will be detected has not been born yet. It is still sitting in its uranium nucleus waiting for fission to happen. So these are really low intensity experiments. Here's an experiment done in 1995 by my student Birgit Doppfer with individual photons. I mentioned before that this Einstein questioned what happens to an individual particle. Here's an experiment where you create pairs of photons. You use one photon as a trigger which tells you that the other one is on its way, and here are the interference fringes, these stripes seen by Birgit Doppfer. The important point is the intensity here. The maximum is 120 in 60 seconds. So in other words, this means that most of the time the apparatus is empty and sometimes you have a photon coming through. The solid line is theory from first principles. No three parameters except the total intensity. A question to be raised is how large can objects become to show this kind of phenomenon? And I mentioned before that I personally expect that there is no limit. The limit is only a question of money. Of money and of experience, of experimental experience. I'm sure we will learn to see these things for incredibly large objects. Here's an example with full arenas, carbon 60, carbon 70. So the question is if things become very massive, will we enter a classical world on itself? The answer in my eyes is no. If they become complex, the answer is also no. Temperature might be different because temperature provides a way for a system to talk to the environment. Here's a sketch of this early experiment with full arenas also done in Vienna in 1990. Sorry, in 2000, in 2010 years wrong. Sorry, in 2000 the experiment with these large bucky balls, not the two-slit but a grating, a multi-slit grating system shown to the lower right here. And these are the interference fringes observed just the same kind of thing as before with the photons but now for carbon 60 or carbon 70 molecules. The interesting point to be mentioned here is the difference between experiment and theory. This is theory from standard optics. This is experiment as observed and it seems that experiment is better than theoretical prediction. The peaks are higher and more well defined. The reason is Casimir interaction. The reason is the fact that the molecules passing through the channels of the interference grating experience the fact that the walls are there and through interaction of virtual particles and therefore they experience a phase which is position dependent and leads to this kind of thing. That is one case of a famous saying by Richard Feynman who said that yesterday's sensation and Casimir interaction was a sensation. There was a Nobel Prize given for the Casimir interaction. Yesterday's sensation is today's calibration and tomorrow's background. In our experiment the Casimir interaction is a background. So I raised the question how large can objects become to show quantum interference. Now the problem is decoherence. The problem is the fact that the quantum system might interact with the environment and that way loses its coherence. One experiment we did is decoherence by emission of thermal radiation. You have your incoming fullerene heated up to quite high temperatures. The temperatures here were of the order of 4,000 to 5,000 degrees Kelvin. It's quite hot. The question is why do the molecules not fall apart at the temperature? The answer is that cooling by emission of radiation is a faster process than breaking apart. So they cool down but they still emit photons and these photons here at the wave fronts emit photons and these photons can tell the environment where the fullerene is. They give the information about the path just as we said before in the Bohr-Einstein dialogue and therefore you have lots of quantum coherence. So decoherence can be seen or understood as a flow of information into the environment and in this kind of experiment one gets very detailed understanding of the mechanism's quantitative understanding which allows one to predict by simple scaling in size and temperature that decoherence will not be a serious problem for molecules as large as small viruses even at room temperature. So if you go to larger objects there's lots of possibilities. There's no serious limits. So these are the interference patterns for increasing temperatures. Here we start at some low laser power and then when we heat up we lost the interference pattern. Okay. So where's the status of this kind of experiment? The record in terms of mass is this molecule. It's a carbon-60 with additional fullerene sticking out carbon-60, fluorine-48. The record in terms of size is this molecule, also benzene, which was done by Markus Ant and his people. He's doing these experiments now alone just about a year ago. This molecule is already very large 3.2 nanometers and it shows perfect interference. So there's nothing which makes quantum coherence go away if a molecule becomes floppy like this kind of thing and might twist around and vibrate in all kinds of things. A very interesting new development in going to larger objects is where people in different places try to put mechanical levers, small mechanical levers into quantum states. This picture is taken by people in my group. These experiments are done by Markus Arsmeier and his students and postdocs. This is a picture of small mechanical levers made of silicon and what you see here are patches of basically anti-reflective coating. This will be the mirrors in cavities where one tries to couple these cavities to quantum states of the radiation field and maybe see some entanglement either between photons and these mechanical systems or between mechanical systems themselves. We talk here about very large masses already. We talk about masses of the order of 10 to the 20 atomic mass units. So this would be a huge step in mass compared to what we have these days. Back to fundamental questions. Here's a picture of fuller rings and classical objects. A tunneling microscope image of these molecules sitting on a surface. And here you see them localized on a scale which is much, much smaller than the scale between the interference paths I showed you before. And this is a fuller ring, a classical object or a quantum object and the simple answer is it depends. The question whether something behaves classical or quantum as Boer always said depends on the experiment you do. The experimenter decides whether a system is classical or quantum by choosing the apparatus. There is no objectivity. So the same piece of apparatus in one experiment can be on the classical side or on the other in another experiment can be the quantum object. So this also means that there is no border between the quantum world and the classical world. It depends on your experiment. Here is a picture taken in an American parking lot. As always, our friends across the pond are far ahead of us. They have... This is a picture Charlie Bennett gave me they have obviously quantum cars which are able to leave a parking lot in a superposition of two possibilities and this picture proves that they exist because a quantum car you cannot observe while it passes through. Right? Okay, so far a single particle interference and now we come to the second part of my talk it's entanglement. This is a very famous paper, 1935 published by Einstein, Podolski and Rosain in the physical review and this paper itself has an interesting history. First, it was never seen by referees. At that time it was just accepted the way and as some of you might know as soon as physical reviews started to send Einstein's paper to referees he never sent them a paper again. Okay? That's a very good position which would not be possible these days anymore but then at that time it was possible. Second interesting point is that this paper was only quoted about once per year until the mid-60s and now it is quoted about 200 times a year. So let's tell you something about the importance of citation indexes and Hirschfactors or whatever. It took 40 years until this paper was appreciated. It's now the most frequently quoted paper by Einstein. In that paper, for those who don't know the story yet in that paper, Einstein, Podolski and Rosain identified that you can have quantum systems which are connected in such a strong way that the quantum states cannot be separated in the individual states by implying that if I do a measurement on one of the systems in the state it instantly collapses, changes the quantum state on the other system no matter how far it is away. Einstein didn't want that, he called it in a derogatory-based bookie action. Schrödinger in the same year coined the notion entanglement for the situation and he said, and I tried to symbolize this here a little bit, he said that the interesting thing is that you can have two processes, namely the measurements on two systems, two entangled systems, where each one is completely random. Schrödinger talks about expectation catalogs, not being defined, but as soon as you measure one the outcome on the other measurement is well defined. Schrödinger says that this is a situation you cannot have in classical physics where you have well-defined expectation catalogs for joint observations but undefined for individual observations. Actually, it turns out that this came out very shortly after the Einstein-Bordowski-Rosen paper that Schrödinger was worrying about this already for a couple of years, as one knows now. Here are a few remarks about the situation. Einstein-Bordowski-Rosen themselves introduced the notion of entanglement of elements of physical reality saying that upon measurement of one system I can predict with certainty what the corresponding measurement on the other system would give me and therefore it makes sense to introduce elements of reality corresponding to this property. And they argue that these elements of reality are not in containing quantum mechanics and therefore quantum mechanics must be incomplete. Famous is the last sentence of the paper where they say while we have thus shown that the wave function does not provide a complete description of the physical reality we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible. Now we know that at least the last sentence of the paper is definitely false. But the rest one can argue that's a question of philosophical position. But the last sentence is certainly false. Here is Bohr's answer in the same year. Bohr never wrote papers in a very clear way, so if you ever read Bohr, read him a couple of times, it takes a while. And he supposedly once said that when people complained about his writing style that he should write more clearly, he said that why should I write more clearly than the way I think? Okay, there's a point to that. Bohr's in his answer, which is quite interesting, basically says that physics is about what can be said about the situation and what can be said about the situation depends on the context of the complete experimental setup. An interesting statement was given by Peres in 2003, and I say this here because I like it very much. This statement here, quantum states are not physical objects. This is quite important. They exist only in our imagination. This is on Bohr's side. In summary, the question raised by EPR can quantum mechanical description of reality be considered complete as a positive answer? However, reality may be different for different observers. So we see here already reality is at stake. Now, this is a Newton lecture. What would have Newton said to this kind of question? There's a letter from Newton to Bentley, probably a precursor of this car company or whatever. Bentley dated February 25 from the winter 1692 to 3. He clearly talks about gravity here. He says it is inconceivable that inanimate matter should, without the mediation of something else, which is not material, operate upon and affect other matter without mutual contact. In entanglement, we seem to have something like that. And then he says that gravity should be innate, inherent, and essential to matter so that one body may act upon another at a distance through a vacuum without the mediation of anything else is, to me, so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it. And I simply took the liberty to replace gravity by entanglement. And then you can accept the same sentence to describe the situation of entanglement. When entanglement, we believe, we seem to believe that there is no mediation of anything between the two observations at the time of the measurement. Now, all this, I mentioned to you before that the Einstein-Botowski Lawson paper was only quoted about once a year until for the first 30 years. And this changed in 1965. John Bell, an Irish physicist, did something very interesting. And he showed that the Einstein-Botowski-Rosen idea if carried through this final sentence would lead to a contradiction with quantum mechanics. The situation is simply that you have a source which puts out pairs of particles here as photons where both photons are either horizontal or both photons are vertically polarized and you do measurements on the polarization on both sides. If you measure the same polarization, you get perfect correlations. But if you measure at a small angle with respect to each other, you don't get perfect correlations anymore but statistical correlation. And it turns out that these statistical correlations are stronger than what a local realistic picture would allow you. And that is the essence of Bell's inequality. What does local realistic mean? Einstein's locality in the words of Einstein is the assumption that for the relative independence of especially distant things, A and B, this idea is characteristic. An external influence on A has no immediate effect on B. And realism, the measurement results are determined by properties the particles carry prior to and independent of observation. There's an interesting situation for three particles. I mentioned before that if you have two particles and for small angles you get a contradiction, you get stronger correlations than what a local realistic model would allow you to do. For three particles it's even more funny if you have three particles, three photons say and you measure the polarization with the three, then there are situations where upon two measurements when you predict the third one, a local realist would predict an exactly opposite state from a quantum mechanics. And this again raises the old question of the debate between Einstein and Bohr. Is physics about what is? Is physics about what can be said? If physics were about what is, then this kind of situation before leads into traverse, it leads into at least the conclusion that the local realistic position is not possible. If physics is just about what can be said, then there's no problem at all. But then we have to answer what is reality. I will come back to this at the end of my talk. Just to make one point clear, which is important, the difference to classical correlations. There's a beautiful paper by John Bell from 1980 with the title Bertelmann's Socks and the Nature of Reality. This is a strange title of a physics paper. Bertelmann wrote it to explain, as he says, to philosophers what the interesting issue here is. There's a physicist called Bertelmann, a real physicist. He still exists. He's in Vienna. He's a colleague of mine in Vienna. He worked with John Bell for a long time in CERN in Geneva. And Bertelmann, Reinhold Bertelmann, his first name is Reinhold, when we go through the kind of formative years, some of us decide to do something to protest against the world. And Bertelmann decided to never wear socks of the same color any more in his whole life. So he still does. He's now obliged to do it. He still does it. So when you see, so what Bell said, when you see Bertelmann coming around the corner, he really looks a little bit like that. When you see one sock, and you see that the sock is pink, then you know definitely that the other sock is not pink. Now this is trivial, because you know that Bertelmann pulls always different socks on in the morning. So that's a very trivial thing, nothing interesting. If these were quantum socks, as Bell argues and shows, if these were quantum socks, then the assumption that they would have these colors before you look at them would be wrong. But more precisely speaking, before the first observer looks at them. So quantum socks, Bertelmann, would have to pull on blind foldedly in the morning. Otherwise the care information is not so trivial. It's more complicated. But that's just to stress again and again, even in books by famous physicists, to read that the situation is as simple as this, which is simply wrong. Now, experiments. Interestingly, this is one of the funny coincidences in science. Bell wrote his paper just when experiments were about to be possible. Just about the time of the discovery of the laser. I mean, what would have happened if he had written the paper much earlier? I don't know. It's an interesting question. So people started to do experiments on entangled photons, on photon pairs. The first experiment was done by Friedman and Klauser. Then there was a beautiful series of experiments by Asper in the 80s and some more recent experiments closing loop holes. I don't want to go into these details. That's the graph from the first experiment. You create your entangled photon pairs. You send them to two analyzers, polarization analyzers. You measure the transmitted photons. In more recent experiments, the setup, this is an experiment we did in Innsbruck a while ago. The setup looks much more difficult. You have a polarizer. You measure both polarizations. You have an electro-optic modulator to change the polarization at the last instance before you measure it, because that way you can exclude any unknown communication. But these are details and not so important for our discussion here. Here's a picture of the way how simple these experiments are today. You can, so what you do is you use a non-linear optical crystal, pump it with some laser. This is a blue laser here. In some experiments we did it with a simple laser pointer. So it's very easy now. We create pairs of photons, couple one of the photons into this glass fiber, the other one to another one, and send it to distant places. These experiments are so simple now that we do them regularly in student laboratories. And many people are talking about producing this for schools, but nobody has done it yet. Then my title, I talk about quantum information, the foundations of quantum mechanics. The big surprise was in the early 1990s for me and for many people working in the field. I'm sure it was a big surprise for you, Peter, also, and for other people. When somebody asked me 20 years ago what this is good for, what we are doing here, these experiments on the foundations of physics, my answer always was honestly that this is not good for anything. This is useless. This is just part of the identity of humans to be curious, to do experiments, to try to find out how the world works. It's just like listening to a Beethoven symphony. But this has changed to my big surprise. There were people who started to have ideas how this might be used and applied in experiments. The central concept is the quantum bit, the qubit, introduced by Ben Schumacher. It's the quantum superposition of two states, zero and one, of a bit quantum superposition, could be, for example, the two paths of state experiment. You can have entangled qubits and so on and so on. It's obvious if you encode information that way then you can do much more than what you would be able to do in a classical situation. Here's an example, quantum cryptography picture. This is actually a picture put together the way it is by Physics World, who are in an IOP journal. This is an article coming up in the next issue in July by Markus Aspermaier and myself about these kind of things. So you create entangled photons which are perfectly correlated in polarization, for example, which means that if you measure many pairs of photons you get the same random sequence on both sides. This was an idea proposed by Otto Eckert in 1990. It was actually, as far as I know, the first paper in quantum information which made it into physical regulators. That's quite interesting for the field. And anyway, Otto Eckert was a student of yours, right? That's right, yeah. So you get random sequences of numbers which you see a graphical representation here and then what you do when you want to encode a message, for example, this picture of the Wieners of Willendorf in FIG found about 100 kilometers from Vienna. You mix them bit by bit. Here's the encrypted message and because the original is random this is secure against eavesdropping but the receiver can decode it. Actually, the reason why we chose the Wieners of Willendorf in these experiments I have said that many times was because we wanted to have a symbol which is certainly not a military symbol and which is Austrian. So this is an Austrian figure and it's most likely not a military symbol. It's actually the first time and probably the only time, as far as I know, that an unclad person was imaged in physical review letters. Nobody complained. Okay, anyway. The status of quantum cryptography is rather mature. There are companies offering simple systems actually not based on entanglement but that's not important and I just want to tell you that there is a European network. There are also some British colleagues participate. It's called SecureQC and we will run a test of a quantum cryptography network in Vienna in October this year. So 8th or 7th or 8th of October. So this will be quite interesting where we show that different hardware built by different groups can connect to each other and exchange quantum cryptographic keys. Here teleportation already mentioned by our chairman. The idea proposed by Bennett Barzakhre chose a pair as Wutas and this is actually an interesting situation to talk about with respect to the Bohr-Einstein debate. The situation is simple. We have Alice who wants to teleport the quantum state, the quantum system in an arbitrary state. This is General Cupid and the way she does it over to Bob, she does it is that Alice and Bob share an entangled pair and Alice does projects these two particles on an entangled state on a so-called bell state. And here is the state which comes out. I apologize to the non-physicists for these equations here but the basic point is that upon measurement here you have a state over at Bob's side which can have four different manifestations which contains already all information which is contained in the original. And then in order to finally get the original state one has to know what the measurement result for Alice was and do a unitary operation here but that's not so important. Now, there's a lot of debate about how does the information in teleportation go from A to B. It does not seem to follow a certain path but this appears here that the original loses its property and it reappears here. Now, if one uses this kind of language one is already in a sense on the realist side. If you're on the side of Bohr then all that happens is that what you can say about the situation depends on what the measurement result is here. It depends on further new information and if that information changes then what you say about the situation i.e. the quantum state at the receiving situation has to change. So for a strict Boolean in a sense there is no problem here. It's just a question of language. Here's a picture of the six people who proposed the Einstein... the teleportation and this is obviously showing a sketch or whatsoever but that is not so important. Here's a picture of an experiment done across the river Danube two years ago teleportation from one side of the river to the other one. I just want to come back to the interpretive question once more talking about this experiment. The idea was put forward by Asher Peres in 2001. The idea simply is that you take two entangled sources and you submit or you don't submit one from each of the pairs to a bail state measurement to project them on an entangled state. Then what happens is that you can view this as teleportation of this state over here or this state over here. What happens is that two photons which never interacted become entangled so far so good and that has been seen in the experiment but the interesting question now is that Alice might receive these two photons at a time when Bob has done his measurements already when all the records are written down and Alice can decide by what measurement to perform whether these records here correspond to photons which are entangled which have been entangled with each other or whether the same records already written down the same records already written down correspond to entanglements between 1 and 2 and 3 and 4 but these are two completely different physical pictures which are mutually exclusive as we like to say that entanglement is there is a monogamy of entanglement you cannot have both entanglement with two different systems at the same time a perfect entanglement. So what happens? How can the decision of Alice at a later time change the physical story behind here the physical interpretation? Now what actually happens and the way to see this is that the events here the events just happen you measure the photon the event just happens there is some classical record but the meaning of the event is the complete story the complete interpretation depends on actions which might lie in the future So again to me this underlines once more that physics is not about what is it's not about what is out there but it is what can be said about the situation what can be said about the situation might depend on actions which are in the future This is an experiment which is going on now in our lab a student of mine is trying to do this experiment where we decide at the last instance when these have been registered already randomly whether Alice projects these on an entangled state or measures them separately just to really confirm that what's going on is what we expect Now how large distances can we see entanglement There is a series of experiments going on some of it in collaboration with people including Rarity in Bristol at the Canary Islands So these are some of the Canary Islands we do entanglement distribution and similar experiments between the two islands of La Palma and Tenerife off the west coast of Africa Now you can imagine that this is a nice place to do experiments You work at two and a half thousand meters above sea level and when there is no fog you work all night to collect your photons The distance between these two islands is 140 kilometers and here is some pictures of the setup that doesn't tell you too much That's the sending station where you have two lenses with which you can send two photons over to a receiving station optical ground station over there on the island of Tenerife Now that's a picture of a beacon laser here The receiving station is a telescope operated by the European Space Agency a telescope which was built for the specific purpose of communication with satellites with important features Firstly it can follow a satellite with high precision and secondly it can go all the way down to the horizon which usual telescopes cannot do so we point the telescope horizontally over to La Palma This mountain is El Teide the highest mountain of Spain There is an interesting connection to Newton again since this is the Newton lecture on La Palma This is the sending station There is a cluster of telescopes It's actually very interesting on Tenerife you have telescopes which are essentially for observing the sun during daylight but Tenerife is highly populated so the telescopes for night observation are on La Palma 140 kilometers away and one of the group of telescopes is called Isaac Newton group actually run by by this country as far as I know by the United Kingdom this is Isaac Newton group and our sending station is a little bit over here over here to the left up on the same mountain Here's a picture of the kind of experiment which we did it's a paper which is about one year old just to show you what happens that is a satellite picture so what you see up there are ocean waves very long wavelength ocean waves and for example you create pairs of entangled photons one is measured locally the other one is sent via these telescopes over to the other station to create quantum cryptography keys for example or to test entanglement now this kind of experiment does not does not test quantum non-locality because the first photon is measured instantly now this year we are doing an experiment where the first photon is delayed so much that the two stations are actually spaced like separated this experiment will start in a week from now and it will be quite interesting again the future is experiments in space we have a program with the European Space Agency to actually build sources for satellites and send photons down to two different locations on Earth the situation is that this kind of project is scientifically accepted we just need the smallest amount of money like about 50 million euros which for space people is actually a small amount it's not very big so we are optimistic that we will be able to put this together in a large international collaboration I want to come back to the fundamental question from Bayesian equality and the experiments we know that local realistic theories are inconsistent with inconsistent with both the predictions of quantum theory and with experimental observation so the question is which assumption is wrong is it locality which would mean that maybe one can work with non-local realistic theories or is it realism which means that one might be able to work with local non-realistic theories whatever that might mean or is it both now this again was just a philosophical question very much as the original Einstein Bodovsky-Rosen question was just philosophical until Bell came along this was just a philosophical question until Tony Lagerd in 2003 proposed a what he called a crypto non-local hidden variable theory it's a theory where you again do measurements on two photons over a large distance where you measure some parameter here and you have some outcomes one and minus one and the assumption now is that the physical states emitted are actually statistical mixtures of sub-assembles with definitive with definitive with definitive polarization okay and the new thing is that that Lagerd allows the measurement result on one side say A on one side depend not only on lower case A which is the setting of the measurement apparatus say the orientation of the polarizer on A but also the setting of the measurement apparatus on the other side and instantly one might think that that way one can do anything but that's not quite true Lagerd was able to show that one can construct a theory which explains all existing experiments and obeys the no signaling condition namely that you cannot send signals faster than the speed of light the new thing in these experiments is that one Lagerd developed an inequality a generalized kind of bell inequality the new thing is that in these experiments one has to measure not only linear polarization but one has to go out of the plane of linear polarization in the Poincare sphere this is the Poincare sphere left to right horizontal vertical polarization one has to measure correlation between linear and elliptical polarization and lo and behold when you do this you arrive this angle phi is the angle by how much you go out of this plane of linear polarization these are the measurement results and here's the limit of Lagerd's theory so lo and behold this theory is also in conflict with quantum mechanics and in conflict with experiments one point is that this kind of experiment would not have been possible like 10 or 20 years ago because you need much higher quality of the entanglement so this is one of the things made possible by the progress in quantum information now what are we left with now what does this situation mean so the issue at stake is whether the locality assumption is true or not it seems to be not relevant the question is to which extent can we talk about a realistic picture of the world or one possibility would be that the world is totally deterministic that we have actions back into the past or that our simple logic is wrong and so on I put big question marks here because I keep saying that we need a philosopher, we need someone like what Emmanuel Kant did for classical physics for quantum mechanics but maybe I'm too romantic in that expectation I want to quote Lagerd again incompatibility between quantum mechanics and these realistic theories has little to do in his opinion I share this opinion with locality but it has much to do with objectivity which is his name for realism and the questions which we can raise now is questions like how strange must the non-local theory be to agree with quantum mechanics there is one, namely non-local theory then an interesting research program might be to classify non-local theories by all kinds of features they might have and see whether we can do new tests a very deep question which I have been fascinated for a long time is can we construct test theory of quantum mechanics like we have it in general relativity it doesn't seem to be possible but the point might be that quantum mechanics is too airtight and the practical question more practical question is to look for multi-particle generalizations of non-local theories just to show you what the experimental experiments are which people have gone through and to see what we might do in the future this is a character these are pictures from this upcoming article in physics world and they did a very nice job drawing them this is the bell type experiment where you measure linear polarization on two photons then this is the three particle correlation experiments where you measure on one photon linear polarization on the other circular polarization and this is the legged type experiment where you measure on one side linear polarization on the other one elliptical polarization so this covers pretty much all bases you can do with two or three photons and it seems that one has to go to higher photo numbers to ask new questions so the question is how to go to higher photo numbers and an interesting line is integrated micro-optics which is being pioneered among other groups by O'Brien in Bristol, was in Australia before that's a picture of a control knot gate he built in jazz fibers micro-optics and there are interesting questions one can ask one can create and measure multi-photon states now in this kind of system I hope with higher purity and so on than one would expect the idea is to integrate this with new sources and with new detectors one can I personally expect that it will be quite interesting to investigate higher dimensional Hilbert spaces one can ask fundamental questions already as some of you know with Hilbert spaces of dimension 6 new things come in the number of mutually complementary bases is an open question for six dimensions and there are interesting questions like there's a beautiful paper written by Conway and Cochin Conway is the person who invented the game of life which they call the free will theorem the free will theorem says that that basically if one if one can assume that the answer of an elementary particle upon certain measurements is random is completely random they say if they have free will then the experimentalist must also have free will which is quite an interesting statement but there are experiments to be done namely experiments in entanglement in higher dimensional Hilbert space and I'm sure that once these experiments are done they will lead to new applications in quantum information so we are at an exciting point right now where the technology to people developed to handle more complex systems just for quantum information might lead to new fundamental questions here's an artist's rendering of eight photon entanglement which I call the quantum crab looks like a crab it's the artist's picture how to imagine that you can have six quantum systems perfectly perfectly correlated with each other I actually like the picture I think it's beautiful so I want to come to an end I don't have a watch beat I think I should come to an end I want to come to an end I should not stop without mentioning quantum computation but I don't want to go into details here there are different paradigms of quantum computation one is where you have a quantum computer which provides a unitary evolution of an input state and you get some output state as the result and there's a new scheme started by Nila Flamilban and proposed by Rausendorf and Briegel where you start with a sufficiently complex state and there's subsequent measurement one measurement after the other one provides the computation which is a very different paradigm than all other computation schemes but I don't want to go into the details here I also don't want to go into the experimental details that's how a typical table looks like this is a small section of this kind of experiment but it's all easy you know what each screw means this is standard fair I just want to say a little bit about the future of this quantum computation stuff I know there are quantum algorithms and the first quantum algorithm proposed was actually by David Deutsch and the first algorithm which can be more efficiently solved on a quantum computer than on a classical computer here's an example of the Grover algorithm which might be interesting for the non-physicists because it shows the potentiality the challenge is the question is you have a phone telephone book and if you know the name of a person you can easily find out the telephone number if you know the alphabet if you don't know the alphabet you have a problem but if you know the alphabet you can easily find out the telephone number but other way around if you know the telephone number it's very difficult to know the name of the person and this is the problem of searching in an unsorted database and it turns out that with a classical computer you look through the whole telephone book to find the right name on the average you have to look sometimes you are successful sometimes you are not on the average you have to make n over 2 look ups where n is the number of entries in the telephone book so if there is a phone book with 2 million users a classical computer has to check 1 million entries which for a million entries is only 1,000 so that is a significant progress but I want to speculate a little bit about the future and what I show you here is called Moore's Law Gordon Moore was the founder of Intel one of the founders of Intel Corporation the company which creates these computer chips and Moore found by simply observation of the technology that the number of elements on the computer chip doubles every 2 years initially and then he revised it to every 18 months so in terms of the physics it simply means that the individual devices the individual elements get smaller and smaller so you have less and less atoms less and less electrons needed to encode one bit and one can estimate that on the timescale of roughly 20 years at most actually if one extrapolates now one arrives at the situation where one bit of information is carried by one electron anymore in these kind of circuits and then we are at the quantum limit so it will happen so therefore I wrote down here quantum information technology will happen by extrapolation extrapolation can bend off, you all know this but it will happen some days and I also would like to predict that quantum computers will not be built to solve exotic algorithms but they might even be used in everyday life I am very optimistic here but I am optimistic because I believe that the problems of decoherence and so on can be overcome now let's go back to the philosophical question once more the question how real is reality do objects exist if nobody looks is the moon there when nobody looks you know there is this famous story that supposedly Einstein asked Bohr do you really believe that the moon is not there when nobody looks and Bohr is said to have answered him can you prove to me the contrary this is very wise it's actually the point that physics is about what can be said about nature rather than about what is now I might speculate a little bit we have this old evolution in our philosophy but also in eastern philosophy that's one of the things I learned in my discussions since you mentioned the Dalai Lama the old discussion between the two extreme camps of idealism and realism in modern language the relationship between information and reality and it seems in my opinion quantum mechanics is about what can be said about the world information seems to be very important in the universe maybe even constitutive to the universe whatever that means and that has been said I couldn't avoid to put that quote down that has been said in Saint John's Gospels the first sentence says in the beginning was the word whatever that might mean in that connection now there is an article written by Hans Christian von Beyer which you find on the net about some of these musings but I want to conclude with a sentence of Newton which I really like he wrote I keep the subject of my inquiry constantly before me the first dawning opens gradually by little and little into a full and clear light maybe this happens someday with these issues about reality and information in quantum mechanics this is my last but one picture my group in Vienna this is one of the big one of the big fortunes of my life and not only of my life is if you look at the picture then this is by far the oldest person on the picture and it's really a big joy to work with these young people at the time with these young bright minds who are full of fantasy and ideas and since I noticed that there are some young people, some students here my last picture is an advertisement together with Harald Fritsch from Munich who is a elementary particle physicist theoretician we are organizing a school in Bartoneff in Germany in September which is called Foundations of Quantum Physics this is an experiment elementary particle together with quantum mechanics we want to see how it goes and if students here this is a physics school if students here are interested just look it up on the website and there are still some openings so if you want to come just write an email to this website and with a little motivation why you want to come and I'm sure you will enjoy it thank you very much for your attention