Klaus von Klitzing (2016) - A New International System of Units in 2018!? How my Nobel Prize Contributed to this Development

Yesterday already, when Professor Feldmann got his birthday present, I was confused and I expected that to be no secret at all. So they would give me also some birthday gift. I’m not smoking so I expected something to eat or to drink or so. Therefore last night I changed a little bit some of my slides. Because I wanted to show you the picture at the time of the discovery of my Nobel Prize winning research. This is the picture. So this is a true story. Now, I do not always have a camera with me when I’m doing some experiments in the lab. But when I got the Nobel Prize, 5 years later after this experiment, journalists wanted to have a picture of the real situation. And this is very close to reality. So I can confirm we had such a situation. You see, at 2 o’clock in the morning in Grenoble - I made the discovery at night. We met always with all the scientists in the lab, and then we had some baguette, some cheese and some red wine. And so this was natural. Since then I have the image that I am a drinker of wine, that I always drink red wine. And even, I had once this Vin Klitzing, this special wine - you see also the Nobel Prize mentioned there: Appellation Nobel controlée, mis en bouteille au domaine Klaus von Klitzing. My students rented a vineyard for one year, so I collected all the grapes. And this is an official wine. If you want to read the story, you could see Vin Klitzing - there’s a chapter in the book of Bob Laughlin. He has written a book A Different Universe. And in Chapter 7 is all the story about the wine and the discovery of the quantum Hall effect. Bob Laughlin got the Nobel Prize in’98. Ok, but now let’s go really to the work. (Laughter) I started 30 years ago with my first Nobel lecture here at Lindau. And very often in the discussion students asked me, ok, how to get a Nobel Prize? And it’s not easy to give an answer. So one answer is: don’t believe what the boss is telling you. Be independent, o what you want to see and to do. But today, for the first time, I have 2 answers to the question, how to get a Nobel Prize. There’s answer number 1: Just cross Lake Constance and eat chocolate - perhaps you know this picture. There is the picture (Laughter. Applause) And then you have to go, not to Austria, but to Switzerland this time, just crossing the Lake Constance. But, you know, such graphs you can manipulate in all kinds of things. Yesterday I learnt, in Germany you also have to eat a lot of chocolate, but the probability is only half. But if you put it against fish consumption and Nobel Laureates or football finalists, then Iceland will be the winner. This was one. Another one is: It's just a question of money. Ok, the Nobel Foundation will not be happy about this, but all Nobel Laureates got perhaps a letter from this auction house. If you don’t need your medal anymore, just give it to the auction. For example, Leon Lederman’s Nobel Prize was sold last year at this auction. So if you have enough money – but, unfortunately, scientists do not have enough money. But if you want at least to touch a Nobel Prize, so this is the Nobel Prize. Come to the afternoon. I don't have the certificate with me, but this is certificate if you get the Nobel Prize. And I will speak about my Nobel Prize and new application of this. So it was discovered, as I mentioned before, in 1980. But I will go back, because this year we are celebrating the 50th anniversary of Quantum Hall Physics. Because already in 1966, if you look at the literature, you can see Quantum Hall Science in the publications. And this was basic research on silicon field effect transistors. You know the principle of the field effect transistor: We have a capacitor, one metal plate on one surface. The other one semi-conductor. There’s a positive gate voltage. One introduces a thin layer of electrons. And these are 2-dimensional electrons, because particle in a box gives you a zero-point energy for this electron. They cannot move perpendicular, they are quantised. So this is a 2-dimensional system. And a lot of research has been done in this field. The interesting point is, the magnetic field is perpendicular to this 2-dimensional system. You can quench the kinetic energy of the motion of the electrons in this plane by the strong magnetic field. Then one has discrete energy levels. So this was known already for a long, long time, more than 50 years. And this is the very first picture filling up discrete energy levels in a strong magnetic field with electrons. So this is the gate voltage. You increase the number of electrons. And then see in the conductivity going up and down, filling up the discrete energy levels. This was the publication from the IBM group 50 years ago. And exactly at these positions we have Fermi energy in the energy gaps. And this is an interesting point. This is already Quantum Hall physics: a 2-dimensional system, discrete energy levels, and Fermi energy in the energy gap. So these experiments, published 50 years ago, started the field of Quantum Hall science. Today there is a lot more activities. And every year something about Topological Insulators, Spin Hall Effect, Quantum Anomalous Hall Effect, Composite Fermions, Anions, Nonabelian Statistics, Superfluidity, Fractional Charge, Skyrmions, Bubble and Stripes – everything you can do with a 2-dimensional system in strong magnetic field. So it’s a wide field but I cannot cover this - there is a whole lecture series. I will just concentrate on 2 publications, 2 books, published in 2015: Introduction to Quantum Metrology and Quantum Metrology. So the name 'metrology' will be the focus of my talk today. And in these books there’s all about atomic clocks, but also the Quantum Hall effect plays a very important role in these books. And you know, metrology is the science of measurements. And all scientists know that all measurements can be expressed by our 7 base units. In biology, in chemistry in high energy physics. In principle, you can go back to these 7 base units: second for time, metre for length, kilogram for mass, kelvin for temperature, ampere for electric current, candela for luminous intensity, mole for the amount of substance. So this is the basis for all measurements and all experiments can be expressed in these. And the kilogram, you remember perhaps, is a prototype. The kelvin: triplepoint of water; ampere: force between wires - these are very good realisations of these units. And we will perhaps have a change in 2 years’ time for all these base units. And today I will give you some idea about the change we expect. And Bill Philips emailed already some public relation from my talk, because this picture is also from NIST. And some months ago I got the email, "Do you intend to talk at the Lindau meeting about the new SI in your lecture? As we get closer to the adoption of the new SI, it seems that it becomes even more important." So we agreed that I would cover this. Because on these cards - everyone would get these as a gift. But Bill showed only the front side - I show you the back side. The back side has the Josephson constant and the von Klitzing constant. Therefore I will make some public relation for these 2 constants. Because they were the origin of the change we expect in the future for our SI system. Ok, Josephson effect, quantum Hall effect, the driving force for the expected change in the SI system. And we heard already about the Josephson Effect: 2 superconductors weakly coupled. Then, without microwave radiation, we have the supercurrent here. And this microwave radiation we have steps in the voltage which are extremely accurate. Independent of the superconductor with 15 digits or more, you have exactly a voltage which depends only on the fundamental constant h/2e and the frequency. So this was the first very important effect for metrology. And then the conventional value for the Josephson constant was introduced in the list of fundamental constants, because everywhere in the world this effect was used for the realisation of a volt. And one should call this a volt 1990, with the index 90, because this was introduced in the year 1990. You can buy such equipment, close cycle cryogenic systems, to have your voltage standard at home. And the same happens with the quantum Hall effect. The quantum Hall effect: a current through a device. And the important thing is, you need this 2-dimensional electron system in strong magnetic fields. And you measure the Hall effect and then the current and the voltage. And in the ideal case, the Hall effect is not a linear function, it’s also a steplike increase. So this is a real experiment. And these plateaus, they have something to do with h/ie^2. Once more, with many, many different materials, different samples, you have the reproducibility with 10 digits for different materials - something very stable. And therefore we have light for the Josephson constant, also or the conventional value of the von Klitzing constant: a fixed value without any uncertainty, just for calibration, outside of a present international system of units. And once more, this Ohm is not our official Ohm in our international system of units. It should be called Ohm with index 1990. And, at the end of this year, Oxford Instruments will sell a system, a quantum Hall system. And this was the publication last year: Operation of graphene quantum Hall resistance standard in a cryogen-free table-top system. And today this graphene on silicon carbide, you can have a situation – this is an experimental curve of the Hall effect and the longitudinal resistance. And you have Hall plateaus, starting at 2 tesla going up to 60 tesla. Just the plateau with a value of 12,906.4035 Ohms. For the negative magnetic field this value, for the positive magnetic field this value. So this Hall effect as a contrast: Hall plateau now for these devices from 3 tesla to 60 tesla. So one can use such a device for magnetic fields in the range between here 3 tesla and here about 14 tesla and temperature range up to 10 kelvin. And currents up to 500 microamps to be in the accuracy of 1 x 10^9. This is now graphene, and there is a lot of activity now in graphene. Originally we used gallium arsenide. In gallium arsenide we have much smaller plateaus. So you see in this space we have only a very small temperature range. Small currents and a small magnetic field range. The accuracy is wonderful. But the range is much smaller. And the other system, the graphene, is insensitive. So therefore we have this comparison. And therefore a lot of groups are not in the metrology institute on graphene. One can combine this, you have the strange value of 12,908 Ohms. But you can produce also 1 MOhm. This is a very recent experiment from the Japanese group: some array of quantum Hall devices in order to produce a nice plateau exactly at 1 MOhm. There is a combination of different quantum Hall devices. And you can combine this in such a way to go very close to the value of 1 MOhm within 3 parts in 10^8. So these are today the modern arrays of quantum Hall devices for metrology. And, as mentioned, you can combine them parallel in series. And for practical application, there’s no doubt that the Josephson voltage and quantised Hall resistance are fixed by the fundamental constants h and e. We have now these quantum units: the voltage, the Ohm. If they are combined, you have the ampere, coulomb, inductance, watt – anything can be expressed or measured experimentally with very high accuracy, now using these quantum units. But on the other hand we have our official SI units. With these base units you can express all the other quantum units. But today, for practical application, we are using the quantum units. And these were adjusted in 1990. So 1990 there was an agreement, but today it starts to deviate from each other. And the new international system of units will unify these 2 worlds. The idea is to integrate now the electrical units, which are artificial units - these conventional values. One will integrate this in our new international system of units. And there was a very important meeting in 2014 at the General Conference on Weights and Measures. They discussed the future revision of the International System of Units, the SI. And they decided to complete all work necessary for the General Conference at the next meeting, the 26th meeting, to adopt a resolution that would replace the current international system with the revised one. The next meeting will be in 2018. And there is a very high probability that in 2018 we will change our International System of Units. At present, all the people who can do high precision measurements of fundamental constants are using the old SI system to determine the value of the fundamental constants. Then you have to submit this to a committee. The deadline is the 1st of July of next year. And if there is an agreement between the different groups, different countries, then one will change the direction. One will fix the values of the fundamental constant and then, on this basis, you have to realise the units. So don’t worry, the new units of our international system will be defined in such a way that nothing will change in our daily life. So you will not see this, the kilogram will stay kilogram. But it will be more stable, more universal. And mainly the kilogram, ampere, ohm, volt, kelvin, and mol will be influenced by these new definitions. And recently, at a conference about the quantum Hall effect, the former director of the International Bureau of Weights and Measures in Paris, in France, Terry Quinn. He did a talk and said, "Key to the new SI will be the redefinition of the kilogram in terms of a fixed numerical value of the Planck constant. Such a definition only became possible with the discovery of the quantum Hall effect." At the time of the discovery of the effect, I never believed that this has some influence on the kilogram. And I will tell you a little bit about the old kilogram. This is our kilogram: "The kilogram is the unit of mass: it is equal to the mass of the international prototype of the kilogram." That is the definition. This was 1901, the year of the first Nobel Prize. They fixed this and they added later a little bit, as I said, after cleaning using the BIPM method. So this is our official definition. If the kilogram disappears, nobody knows what a kilogram is. If you want to see the kilogram, you have to go to the BIPM in Paris. They have a very nice garden there, it’s a nice institute. And if you want to see the kilogram, you have to go into this building and to look at the safe. And I have here a video: Once a year there is a conference and there are 3 different organisations which are interested in the kilogram. They have the key to the safe and the director of the BIPM has the code of the safe. Once I had the offer to be the Director of this institute. But the contract says, you have live in the building to take care of the kilogram. (Laughter) So the one key, second key and then they open the safe, and everyone is happy that the kilogram is still there. (Laughter). Now they are clapping hands. (Laughter. Applause). This is the important kilogram. Now, from time to time one compares this prototype against the copies. Each country has a copy. And then they discovered there is a drift, a drift between the prototype and the mean value of all the other ones. You can say, ok the prototype becomes lighter or all the others become heavier. Today we have the feeling that the prototype becomes lighter. Because the melt was slightly different and one has the impression that some gas is diffusing out of the prototype. This is today the scientific stance. So we have a kilogram definition, which is not stable. This is terrible, I think. And a new problem appeared in 2014: the reference kilogram at BIPM, which is used for the dissemination of the unit of mass, has been damaged, there was some scratch at the bottom. If you put it on the balance, there is a danger that you scratch it. And there was a jump in the mass of 37 micrograms. So you have something which is not stable. And then you can see: Official prototype of kilogram mysteriously losing weight. (Laughter) Or a "Dump the lump" for radical targets. And already in 2005, mainly the NIST discussed some ideas to an electronic kilogram. And for this electronic kilogram the Josephson effect and the quantum Hall effect is important. And you can build it by yourself. So this is a Lego so-called watt balance. So in principle just a balance: on one side the force by mass and here the force by some electrical current. And you have to balance them. And the electrical quantities, if they are measured in quantum Hall effect and Josephson Effect, currently you end up with a Planck constant for the product of voltage and current, which is important in this experiment. So if you want to do this, the Planck constant has a one to one relation to the mass. And up to now very accurate values for the Planck constant are obtained using such type of experiments. In the archive you can find this Lego watt balance, an apparatus to determine a mass based on the new SI. So once more, in the future the Planck constant will be fixed and then you can do your experiment with the mass. And I got this video from NIST, when they built up the new kilogram. So this is the new kilogram, and Bill knows this is just close to his office. This is the new kilogram here. Just last week, there was a publication, 'A precise instrument to determine the Planck constant and the future kilogram', from the NIST group. And the uncertainty is 3 parts in 10^8 at present for these experiments. And this is good enough to change already the direction. But the question is whether the other countries, the other groups, the other experiments will give the same value in the same uncertainty. So you see BIPM, all over the world. You see this watt balance I have here in Korea. There is a watt balance in China. They have also an electronic kilogram here. And these are the points in the world, where they have built up now these so-called watt balance to have their own kilogram when we have the new definitions. Then you have not to go to Paris to know what the kilogram is. Now the interesting point is: do all the different experiments give the same value? And you see the collection of data now. And the quest is to be in this red bar for the final definition. So if you have this collection of data, ok, you may move it somewhere here in this range. And I think, in the future one will agree somewhere perhaps in this range. Now the interesting point is not only the watt balance. There is another experiment which gives you a very good value for the Planck constant. And I will mention it, this is the so-called Avogadro project. The Avogadro project gives you also value for the Planck constant - you see the green points. They have even sometimes a smaller uncertainty, and they are very close to this value. I am very optimistic that they will agree in 2017 or ’18, and they will fix the value somewhere in this range. Now I will just explain how you can determine the Planck constant by the Avogadro project. If you have this equation for the Rydberg constant - the Rydberg constant is very well known. And you have then the fine structure constant which is known as 10 digits. The velocity of light is a fixed value. The only question is: you have electron mass. And in order to have a connection between atomic and macroscopic masses, you need the Avogadro project. The Avogadro project is just to have the bridge between atomic quantities and macroscopic quantities. And this was a world project, the Avogadro constant: counting atoms of a single-crystal in a silicon sphere. And just last week I was at a conference at PTB: Round and Ready – dissemination of the kilogram via SI spheres. Because if you fix Planck constant and elementary charge, velocity of light. The principle from the de Broglie wavelength. You can say, ok, you have some connection between mass and fundamental constant. It’s not done in this way but, in principle, by fixing fundamental constant we have access to atomic masses. And then we need the Avogadro project, in principle, to transfer this microscopic mass to macroscopic mass. As a scientist I have the feeling, a better way would be to define the mass of a silicone atom or some atom. But then we will not fix the Planck constant and we cannot indicate the electric units. So we will not have a new definition that a certain number of atoms is a kilogram – this will not be the definition, it will be the Planck constant. So we have here now the old kilogram, the silicon sphere or the watt balance, and all of them give then access to the Planck constant. So this is the idea, starting from the old system, going to a reference, a new system of constants of nature. The Planck constant, elementary charge, Boltzmann constant, Avogadro constant, velocity of light will be fixed numbers. And this will form the basis for the new SI. So the Avogadro project and watt balances allow high precision measurements of the Planck constant. At present, I have the feeling the watt balances are built up in many countries and seem to be the best way to realise the unit of mass on the basis of a fixed value for the Planck constant. Quantum Hall effect, anyway, will play an important role in our new international system of units. And this new development was triggered by basic science on a silicone field effect transistor. So you never know in which direction you suddenly find some explanations. If you want to have a quantum Hall effect and fundamental constant, I have a video on my homepage called 'A Universal Language', showing the connection between fundamental quantum Hall effect, fundamental constant and the new SI. And thank you for your attention.

Klaus von Klitzing (2016)

A New International System of Units in 2018!? How my Nobel Prize Contributed to this Development

Klaus von Klitzing (2016)

A New International System of Units in 2018!? How my Nobel Prize Contributed to this Development

Abstract

The International System of Units (SI units) forms the basis for all measurements. With the Meter Convention in 1875 a worldwide system of units was introduced with prototypes for the meter and kilogram. Even today the kilogram prototype is by definition the unit of mass.

Long-term comparisons of the kilogram prototype with other mass standards indicate that the prototype is not stable with time so that the General Conference on Weights and Measures at his last meeting in November 2014 published a resolution with the recommendation to define the SI units in terms of invariants of nature. Quantum phenomena in solid state physics play a crucial role in this development.

The talk summarizes the application of the quantum Hall effect in metrology with the focus on the replacement of the kilogram by a fixed value for the Planck constant.

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