Netscaler Exchange 2010 Outlook everywhere prompt

Low Temperature Sciences

I hope this talk will provide interesting suggestions for the students in the audience, but I believe it will provide useful information for all of us. I will use a few photos during my presentation for illustration purposes - for example, here you can see the Golden Gate Bridge in San Francisco. First of all, I would like to discuss the first of my three theses: The discoveries that have most clearly changed our view of nature cannot be foreseen. How are these discoveries made and are there suitable research strategies that significantly increase the chances of a discovery? And here you can see part of the Grand Canyon at sunset. I will explain this thesis on the basis of a series of interrelated discoveries and inventions, starting with this gentleman: Heike Kamerlingh Onnes. Kamerlingh Onnes competed with Dewar to see who would be the first to liquefy the lightest and most inert gas of the atmospheric gases. Before the beginning of the 20th century, i.e. around 1890, Dewar seemed to have won this competition with the liquefaction of hydrogen. Eventually, however, Kamerlingh Onnes managed to obtain a sufficient amount of helium - about a small balloon full - and to liquefy it in 1908. Then he proceeded with the liquid helium in the same way as Dewar had previously done with the hydrogen, he pumped the vapor out of the liquid, which thereby cooled even further and examined the temperature at which helium solidifies. At Dewar, this task was still quite easy. He started at 21 degrees Kelvin and one atmosphere pressure and found that hydrogen solidifies at 14 Kelvin under its own vapor pressure. Kamerlingh Onnes, on the other hand, was not able to solidify helium even after two years. I myself have cooled liquid helium to 1 / 10,000 Kelvin and it was still in a fairly liquid state. The reason for this can be found in quantum mechanics and Heisenberg's uncertainty principle. I do not want to go into this in more detail now, as you are all probably familiar with the connections - only then was quantum physics just in its infancy. After Kamerlingh Onnes had not been able to carry out his most important task for more than two years, he did not give up. Rather, he was now on the lookout for an interesting current problem for which he could find a solution with his new freezer system. It was debated at the time to what extent the conductivity of metals is changed when they are cooled down to temperatures close to absolute zero. On the one hand, it was argued that with very pure metal, the lattice vibrations are eliminated during cooling. And one has to bear in mind that this was only a few years after the discovery of the electrons. It is astonishing that such discussions were even possible at this point in time. Now one had the idea that the electrical resistance would slowly go to zero by eliminating the thermal lattice fluctuations. However, there was another line of thought according to which the conduction electrons in the metal condense again on the ions from which they were given off. The system would be completely neutralized and the electrical conductivity would be canceled. Kamerlingh Onnes then gave his doctoral student a very pure mercury sample and asked him to measure its electrical resistance at very low temperatures. At this point I have also listed the name of the student in question, his name was Gilles Holst. I could imagine that in the days of Kamerlingh Onnes it was not necessarily the rule to mention the names of your students in your writings. With that in mind, I'm glad I wasn't born around that time. The values ​​shown here as green dots correspond to the resistance as a function of the temperature. As you can see, the resistance slowly decreased towards zero as the temperature decreased. But then there was a sudden drop in resistance to a value below 10 to the power of -5 ohms. This was the dissolution of your instrument. Gilles Holst spent a while convincing his mentor that this was not simply due to a loose cable. Of course, the measurements were repeated and this was ultimately the first evidence of superconductivity, which has been investigated every year since then. In the following 15 years, however, anyone who wanted to research superconductivity had to visit the Kamerlingh Onnes laboratory in Leiden, as these extremely low temperatures could only be achieved there. its liquid cryogenic helium 4 to a temperature of 2.17 Kelvin without recognizing or realizing that the liquid helium itself went through a transition phase into the superfluid state, which was just as extraordinary as the superconducting state itself. Incidentally, the subject of his Nobel Lecture was superconductivity, or at least the extraordinarily unusual measurements they had carried out. Kamerlingh Onnes had mentioned in his laboratory reports that the helium stopped boiling at a certain point at 2 Kelvin, but in fact he never investigated why. But let's take a look at which research strategies made this discovery possible in the first place. First there was the use of the best technical equipment available. In this case the liquefaction plant developed by Kamerlingh Onnes, which enabled him to investigate a previously unexplored area of ​​physics. However, he did not reinvent the technical equipment that was already available, but borrowed the Dewar flask invented by Dewar for this purpose. Kamerlingh Onnes was lucky to be able to borrow this vessel, although he was in intense competition with Dewar. For me the really crucial point is that even though Kamerlingh Onnes gave up his attempt to determine the solidification temperature of helium after two years, unlike Dewar, he continued to investigate the low temperature range. He was simply looking for a new task - and I am convinced that failure in general can be understood as an invitation to find a new approach. So don't let defeat put you off your path completely. And pay particular attention to the subtle and unexplained reactions, take them seriously. Because nature often does not knock loudly and audibly, but rather whispers very softly. And when you discover these delicate signs, interesting physical phenomena can be hidden behind them. Well, none of them got the Nobel Prize for discovering the phase transition from helium 4 to the superfluid state. You already knew about the phase transition itself, but couldn't exactly understand how it actually happened. The closest to the solution came this gentleman - Pyotr Kapiza, who in the harsh Moscow winter of 1957, sorry it was 1937, found that the viscosity of liquid helium 4 below this temperature was less than 1 nanopoise. For this he received the 1978 Nobel Prize for Physics together with two scientists whose research area really had little to do with his - Penzias and Wilson. By the way, Arnold Penzias was the boss of my boss at AT and T Bell Laboratories for many years. Penzias and Wilson benefited from the fact that AT and T were experimenting in the field of communications satellites. This gave them a high-tech system from AT and T that they used to study radio signals from space. And here you see this high-tech system. It is a horn antenna that actually has many advantages. It does not detect signals coming from the ground. What was really interesting, however, was the very special low-noise amplifier inside. We owe this to the following gentleman - Charles Townes, the inventor of the measles. This is the second maser, specifically an ammonia maser for high resolution molecular spectroscopy at Columbia University. Only a short time later, Charles Townes discovered that the effect of this maser can also be used to amplify weak microwave signals. In this shed there was a ruby ​​wand that was cooled to a temperature of 4.2 Kelvin and amplified the microwave signals without creating any significant additional noise. The whole system, i. H. the antenna with the amplifiers had an integrated noise signal of 19 Kelvin. This was an excellent value at the time. Here are the first dates that I have to explain to you in more detail. It is a strip of paper from a strip pen. Today's students probably don't even know it anymore. Well, with the tape recorder, the paper strip runs under a pen that moves back and forth in a horizontal direction and thus in this case records the signals coming from the antenna. Then they built in a switch, namely a microwave switch, which enabled them to compare this signal with the signal from blackbody radiation at a temperature of 4.2 Kelvin. That then corresponds to this signal here. They then made a few more adjustments and came to the conclusion that the system still had noise signals that apparently came from the antenna - even though the antenna tip was in a position in space where it was known that there were no radio sources. The noise was 3 Kelvin. They then went back again, examined their equipment and found that pigeons were nesting inside the antenna. Now everything seemed clear to them, they removed the pigeon nest and the bird droppings and replaced some corroded copper plates, which they soldered back into their original position. But the desired success did not materialize, the noise was still there. In addition, it was not restricted to particular positions in space - however you directed the antenna, the noise signals remained unchanged. This irritated Arnold Penzias in particular, and in a conversation with Professor Burke at MIT, he suggested that he contact Professor Robert Dicke at Princeton University. His team included a certain Professor Peebles, who had proposed a theory according to which, during the expansion of the universe as a result of the Big Bang, radiation separates from matter as soon as it is neutralized, i.e. when the electrons and protons combine to form neutral hydrogen . So they looked for precisely this magnetic remanence. At that point in time, i.e. 1964, I was a newbie at Caltech. Later, however, I was lucky enough to be on board with David Wilkinson on the committee. David Wilkinson was on the Dicke team and was there when Penzias put the call through. Later he described to me how Dicke asked if Penzias and Wilson had tried this and that and what the exact conditions were. Finally, he announced that his group would be coming to Crawford Hill to look at Penzias and Dicke's records. Then he hung up, addressed some members of his team who were in his office and said to them "Gentlemen, someone got ahead of us". Thick was researching exactly in the same direction, only his receiver system was based on a conventional amplifier tube and had an integrated noise temperature of 2,000 Kelvin. Let us now look at the research strategies that led to this discovery, which Penzias and Wilson found accidentally. First there is again the use of the best available technology, which was made available by AT and T, i.e. a substantial part of the necessary equipment was borrowed. But then they combined that equipment with a critical component that enabled them to make absolute noise measurements, the very first absolute measurements of radio signals from an alien source. If one now considers the area of ​​the unexplored parameter space, then here too they were the first to carry out such absolute measurements. Ultimately - and this is of crucial importance for scientists in research - one has to understand what exactly the measuring devices measure. If you have no confidence in the measurement results of your equipment and observe the slightest deviation from the expected result, then you will probably attribute this to the fact that you did not understand your measurement devices correctly. In this case, there is a high risk that you will miss something - as I said, nature does not knock loudly, it just whispers very softly. Well, in the meantime there was of course the COBE satellite project - which led to these data, i.e. the intensity of the radiation as a function of the wavelength at a temperature of 2.725 Kelvin. In my opinion, the temperature variations of the radiation depending on the position in the sky, which are entered here via galactic coordinates, are even more interesting. In one direction, i.e. in the direction of movement through the local universe, a Doppler shift of the radiation to a higher temperature and in the opposite direction to a lower temperature can be observed. You can just eliminate this bipolar effect and then you see the plane of the Milky Way Galaxy. This is a little more difficult to eliminate, but afterwards these fluctuations remain, which are typically in the order of a few millionths of a degree, i.e. they are very low values. The people who developed this project and looked at these fluctuations realized that these reproducible signals - tiny as they were - were evidence of temperature fluctuations. These, in turn, were due to density fluctuations in the universe at the point where matter and radiation separate from each other. So this is indeed an extremely active area of ​​research that allows us to study the nature of the universe 400,000 years after the Big Bang. The WMAP satellite followed, with the W standing for David Wilkinson, who sadly passed away before the satellite was put into orbit. This is one of the many problems with such long-term projects. This radiation has a very detailed structure and a multipole expansion of the position spectrum then shows that the fluctuations agree with many models, including the inflation model. For this work within the framework of the COBE satellite project, John Mather and George Smoot, whose contributions you have already heard here, received the 2006 Nobel Prize in Physics. And now we come to the second of my three theses, i.e. that progress in science often leads to inventions or technologies that have a direct benefit for humanity. However, it is impossible to foresee exactly where progress can be expected in solving the problems facing humanity. This is the opposite problem. For example, one may have developed a technology and not know where it is going. But when you have specific needs, it is extremely difficult to say where this technology will emerge. If you take the very remarkable example of nuclear magnetic resonance (NMR) - by the way, here you can see the Iguazú waterfalls, which are located on the border between Brazil and Paraguay - no excuse me - between Brazil and Argentina, they are also very remarkable. Make sure to check them out when you get the chance. So NMR was invented in 1946 by these two gentlemen: Felix Bloch from Stanford University and Ed Purcell from Harvard University. While I knew Ed Purcell personally, I never saw Felix Bloch. Well, when the two of them traveled to Stockholm six years after the invention of NMR for the award ceremony, they were certainly asked what NMR would be useful for - after all, a good 20 years after the discovery of superfluid helium 3, I am also one of many been asked what this was good for. I spoke to people at Stanford who assured me that when asked what NMR was good for, Felix Bloch replied “for very little”. For Felix, the investigations they carried out on the distribution of charges in atomic nuclei had absolutely nothing to do with solving human problems. Ed Purcell was a little more careful and said that NMR could perhaps be used to calibrate magnetic fields. Let's take a look at how things went on with NMR - after all, it was possible to generate very homogeneous magnetic fields with it. When the protons were examined in an organic solvent, it was found that the protons did not all vibrate at the same frequency; there were triplets and quartets. These were due to chemical and spin shifts in the molecules. NMR thus became an important tool for organic chemists around the world. Richard Ernst combined the Fourier transform infrared spectrography developed by Erwin Hahn at the University of California, Berkeley with NMR.In collaboration with Kurt Wüthrich, he was then able to carry out what is known as two-dimensional NMR. But here it was about frequency dimensions, i.e. one tilted a spin and then examined how it influenced the frequency of another spin. This gives information about the bond length. For this work Richard Ernst was awarded the Nobel Prize in 1991 - not for physics but for chemistry. Kurt Wüthrich continues this research and was finally able to demonstrate the three-dimensional conformation of even the smallest proteins in an aqueous solution. Here you can see the trypsin inhibitor from the bovine pancreas - probably the best-known protein structure. In 2002 Kurt Wüthrich received the Nobel Prize in Chemistry for his work. But we're still far from the end - in the early 1970s, scientists discovered that you can get information about the position of the individual nuclei that contribute to the NMR signal if you do not apply a very homogeneous magnetic field, but one with a gradient, ie the magnetic field is wider at the bottom than at the top, for example. If you now do this over three dimensions, you get such beautiful MRI images. Well, I've had MRIs of both of my knees myself - mine don't look as good as this healthy knee here. For this purpose, Paul Lauterbur and Peter Mansfield shared the Nobel Prize in Physiology or Medicine just one year after Kurt Wüthrich was awarded the Nobel Prize in Chemistry. I should tell you - but no, we'll get to that later. I think it is possible that a fifth Nobel Prize will be awarded for NMR - in the early 1990s, Seiji Ogawa, who works in the Department of Biophysics at AT and T Bell Laboratories, made a completely unexpected discovery. When examining the brain of rats, he found that with pulse sequences that are dependent on the speed of the protons when moving along the magnetic field, the brain areas in which information is processed can be mapped, as these are influenced by the blood oxygen content . This functional MRI - also called fMRI - is gaining increasing importance in psychology and is thus transforming a social science into a natural science - a really amazing phenomenon. I want to concentrate on my own discoveries in the remaining time, as I understand a little more about them. I want to show how it really was that we had no clue what we were discovering when we discovered it. And I believe that this is often exactly how it works. The history of Helium 3 is very interesting, there are not enough quantities to get a pure sample. In 1948, Ed Hammel, who worked at Los Alamos National Laboratory, was the first to liquefy helium 3 and measured the vapor pressure above the liquid. Ed Hammel was part of a team that was working on the hydrogen bomb and thus had lots of tritium. As is well known, tritium breaks down to helium 3. In the 1950s and also in the 1960s, low-temperature physicists all over the world investigated the properties of liquid helium 3. The topic was interesting because the helium-3 atoms have a net spin of ½, ie they are Fermi particles like conduction electrons in metals. The behavior is largely identical. In 1957, Bardeen, Cooper, and Schrieffer published their superconductivity theory, and soon some theorists, such as Philip Anderson - a good friend of mine - realized that this theory needed to be modified so that other Fermi fluids could behave similarly at low temperatures . In the first published study in 1959, a transition temperature to the superfluid state of 80 milli-degrees was given. Within six to seven years, scientists had reached temperatures as low as 1/2000 degrees and could not detect superfluidity. according to the doctrine as a pure mirage - like phenomena after smoking substances that one should rather not smoke. Well, when I came to Cornel, new freezing technologies were developed there, such as 3He / 4He mixed cooling, which I saw as a promising basis for a new approach to looking at nature in a different context. For this reason I joined the group of low temperature physicists. This decision was then sealed by a lecture by Bob Richardson, who may even be sitting here in the audience ...? So the lecture was about a thesis by Isaac Pomeranchuk, a member of the Landau School, which he put forward in 1950, i.e. one year after the publication of the results of Ed Hammel's team. He had observed little interaction between nuclear spins in the solid phase and found that the system had an entropy of r log 2, i.e. only 2 available states down to a very low temperature. In the liquid state, the entropy would decrease more quickly; in the case of a disintegrating Fermi liquid, the decrease would be linear, as in the case of conduction electrons in metals. Below a temperature at which these two curves intersect, the liquid would then have an ordered structure and be solid - that was a very unusual system. It was therefore easy to calculate that the latent heat of solidification had to be negative. If you now started with liquid helium 3 and increased the pressure by reducing the volume, the melting curve was reached and the temperature gradually decreased along the melting curve to ever lower values ​​until one finally reached a very low temperature. This results in a cooling of 1 milligrade for every percent of liquid that has been converted into the solid phase. This is exactly what fascinated me about low-temperature physics - and in the second year of my postgraduate course, after my surgery on my right knee while convalescing in the hospital, I developed the following cell - that is the Pomeranchuk cell that I used when I discovered the superfluidity of helium 3 used. Since Helium 3 is very expensive, I have shown it here in gold. In order to achieve a solidification, one must now reduce the volume of this container, for this purpose the metal bellows is moved inside. To measure the temperature, we observed the polarization of platinum cores along the weak magnetic field with the help of NMR and simultaneously measured the melting pressure independently of this. This is the data I got - it was an experiment that was completely - well, that actually couldn't work at all. Unfortunately, I cannot explain that at this point, as it would go beyond the time frame. The capacity is shown here, the pressure increase is shown in the vertical direction along the y-axis, while the time runs to the right along the x-axis. In fact, the system is cooling because the melting curve has a negative slope. I then balanced the system and the cooling stayed - at the point that I later designated as A, you then saw a drastic decrease in the cooling rate. I wasn't very happy about that and assumed that the metal bellows pressed against solid helium 3 and thus triggered irreversible processes. I had started the experiment at 22 milli degrees and realized that if I pre-cooled the liquid helium-3 sample over the long weekend - it was Thanksgiving - I could start at 15 milli degrees the following Monday. This corresponded to the base temperature of my 3He / 4He mix cooler. I then ran the experiment again and got a completely identical curve. In view of the different starting conditions, it seemed to me very unlikely that the pressure that was restored to 1 / 100,000 was the result of accidental heating, but rather that it was an indication of a completely unexpected phase transition within the mixture of helium 3 in liquid and solid form . I then let the sample cool down further to a temperature of 1.6 millikelvin - we know that today - and actually observed a tiny drop in pressure. This in turn indicated a second transition. The question now arose whether the transition took place in the liquid or the solid phase. Finally, I developed a very early version of magnetic resonance imaging. Here I created a magnetic field gradient, i.e. the field was wider at the bottom than at the top. When I then applied a simple radio frequency to the NMR foil, I only received a thin resonance layer with a magnetic field that had the appropriate value for the frequency. Then if I increased the frequency, the resonance layer moved down, etc. This is a CW version of a one-dimensional MRI. I asked Paul Lauterbur during his visit to Bell Laboratories if he had read my studies. He confirmed that he had read them in 1972, the year they were published. Well, I didn't ask him the obvious question as to whether this fact influenced his decision to continue working in the MRI area. In fact, he took it up again in 1973. Unfortunately, he has passed away in the meantime, so I can no longer ask him. Here is some data we collected - in this case, the time history is shown to the left on the x-axis and the pressure increase is down on the y-axis because I flipped the data. You can think of NMR as resonances upwards, but actually they go downwards. So here it goes from the low frequency to the high frequency, from the high frequency to the low frequency and from the low frequency to the high frequency. And there you can also see the large peaks, i.e. solid phase peaks, but a liquid signal also appears in between. So we were able to distinguish these two signals. At transition point B, shown here, all solid phase peaks dropped a few percent, i.e. 1 to 2 percent. Only a few days later - the data was recorded on April 17th - I analyzed it again on April 20th and found that the liquid signal had fallen by 50% rather than 2%. At that time, i.e. at 2:40 a.m., I noted in my laboratory report book that it was a wonderful time for physics. Very quiet, no distraction, less electrical noise, less vibrations - just a wonderful time. Discovered the BCS junction in liquid helium 3. Well, actually, I had only come to this conclusion because I hadn't fully understood the BCS theory. These are extremely unusual BCS conditions, the first to be recognized. That was April 20th - early June, when Dave Lee and I still thought that the A transition was in the solid phase and the B transition was clearly in the liquid phase. We then eliminated the magnetic field gradient and mapped the data as a function of the frequency. We wanted to see if the solid phase signal shifts as it cools. However, we noticed that the liquid signal shifted, which was completely unexpected and incomprehensible to us. When the study was published, we published the results but did not label them as a BCS condition. It wasn't until Tony Leggett got his work done, which was remarkably quick indeed - Tony then shared the Nobel Prize with others in 2003. Well, I'm sure you mean to tell me I only have five minutes. We are also almost through - strategies - looking at nature from a different perspective or in a different context. There really is a way to discover interesting physical phenomena. And you will remember that I described one of my experiments as completely hopeless - but failure in particular can be an invitation to try something new. And that's exactly what I did, spending a little time on other work. Research done out of curiosity is fun, it pays off, and it doesn't take that awful lot of time. And when you're still studying, don't make too many commitments. Had I taken classes in ballroom dancing, even though I would have chosen conversational Chinese because my wife is Chinese, I would have been left behind without the equipment that forced me to do experiments that I had never planned. Then I would certainly have made further progress with my Chinese language skills. It is crucial that successful research does not follow a certain schedule. Finally - and this applies to everyone - you take some distance from your work from time to time in order to look at the task at hand from a different perspective. You become operationally blind and you often focus too much on your work. So now we are at the end. In this picture I am getting the Nobel Prize - I have a problem with Nobel Prizes. You look at them and think "that was Osheroff". To be correct, one would have to say it was Osheroff, Richardson and Lee - and that is not true either. Here you can see once again our circle with the names of all those involved, i.e. the people who made our discovery possible with crucial information or technologies - there are 14 people here and I could just as easily have named 24. Advances in science are not made by individuals, but are the result of developments in the scientific community around the world, asking questions and creating new technologies to answer those questions and share their findings and ideas with others. In order to enable rapid progress, research needs to be promoted on a broad scale and scientists need to be encouraged to exchange ideas and spend some time together to satisfy their curiosity. And that is exactly the way to advance in science! Thank you for your attention.