Do you remember your first computer? Mine was a Mac Plus that possessed a random access memory (RAM) of 1 MB! In 1987 this was enough to run the first version of MacRepertory; now not enough to save one snapshot! In 25 years the technical abilities of computers have skyrocketed, and the impact of new developments in the coming 25 years can only be imagined. For homeopathy the video and the computer have had huge influence. Video cases improved the quality of teaching tremendously. Who can better teach you a remedy than a patient telling you about his state? Earlier we could read or hear about a remedy, but now we could, as it were, taste it. A huge difference similar to reading about a red fruit the size of a chestnut, with tiny seeds on its surface and then getting the opportunity to taste the real thing – a strawberry. A complete library of homeopathy books can now be on your hard disk, and what is more, you can search in it at an amazing speed. What will be available to us in 2037? A development that may open incredible new vistas, also for homeopathy, has been set in motion by Dutch nanoscientist Leo Kouwenhoven . He caused great excitement among scientists with research published in Science in April 2012. In the 1930s, the brilliant Italian physicist Ettore Majorana deduced from quantum theory the possibility of the existence of a very special particle, a particle that is its own anti-particle. That Majorana fermion would be right on the border between matter and anti-matter. Leo Kouwenhovenʼs research group managed to create a nanoscale electronic device in which a pair of Majorana fermions ‘appear’ at either end of a nanowire. The discovery of Majorana fermions opens up a new and uncharted chapter of fundamental physics; they may also play a role in cosmology, as a proposed theory assumes that the mysterious ‘dark matter’, which forms the greatest part of the universe, is composed of Majorana fermions. Furthermore, scientists view the particles as fundamental building blocks for the quantum computer. Such a computer is far more powerful than the best supercomputer because it has the ability to be in more than one state simultaneously. Whereas digital computers require data to be encoded into binary digits (bits), quantum computation utilizes quantum properties to represent data and perform operations on these data. So far quantum computers have only existed in theory, now they may soon become a reality. In 2037 your quantum computer might record everything your patient says while simultaneously analyzing the information and comparing it with a huge memory of provings, materia medica and cured cases. By the time the interview is over and 3-D photos of the patient, DNA and all sorts of physical parameters have been entered into the equation, a differential diagnosis of homeopathic substances is proposed together with a calculation of the likelihood of a substance being the simillimum. This seems a possible scenario. Whether it would actually still involve you or whether the patient would simply run an app at home – who knows? You and homeopathy may have moved on to completely new ways of determining, creating and applying the simillimum. Practically all theoretic particles that are predicted by quantum theory have been found in the last decades, with just a few exceptions, including the enigmatic Majorana particle and the well-known Higgs boson. But Ettore Majorana the person is every bit as mysterious as the particle. In 1938 he withdrew all his money and disappeared during a boat trip from Palermo to Naples. Whether he killed himself, was murdered or lived on under a different identity is still not known. You donʼt withdraw your money and then kill yourself, do you? But then he did write what seems to be a suicide note. Was he killed by the Nazis because he refused to be involved in developing a nuclear weapon, or because they feared he might do so for the allies? Was he indeed seen in Argentina? No trace of Majorana was ever found. As if he had merged with his own anti-particle. As if he changed roles with the mysterious dark matter the particle named after him possibly explains. Could homeopathy offer an answer as to his state and possibly his fate? Itʼs tempting to at least have a look at Origanum majorana . The remedy has suicidal disposition as one of its known symptoms. The Lamiaceae are ambitious and have a great need of acknowledgement. Ettore Majorana was extremely brilliant, which would be a good way to get recognition, but theoretical physics and the sphere of action for which Origanum is known donʼt really seem to compute. Also praise may not have been an important motivation for him as he left writing a paper about another discovery he made to James Chadwick who won the Nobel Prize for it. We could analyse the books and films made about Ettore and speculate about his remedy. But we may better wait until 2037, then feed all personal writings by Ettore Majorana, his DNA and his photo into the quantum computer that he should posthumously receive a Nobel Prize for, and accept the – also posthumously – suggested remedy as his most likely simillimum. Harry van der Zee
Do you remember your first computer? Mine was a Mac Plus that possessed a random access memory (RAM) of 1 MB! In 1987 this was enough to run the first version of MacRepertory; now not enough to save one snapshot! In 25 years the technical abilities of computers have skyrocketed, and the impact of new developments in the coming 25 years can only be imagined. For homeopathy the video and the computer have had huge influence. Video cases improved the quality of teaching tremendously. Who can better teach you a remedy than a patient telling you about his state? Earlier we could read or hear about a remedy, but now we could, as it were, taste it. A huge difference similar to reading about a red fruit the size of a chestnut, with tiny seeds on its surface and then getting the opportunity to taste the real thing – a strawberry. A complete library of homeopathy books can now be on your hard disk, and what is more, you can search in it at an amazing speed. What will be available to us in 2037? A development that may open incredible new vistas, also for homeopathy, has been set in motion by Dutch nanoscientist Leo Kouwenhoven . He caused great excitement among scientists with research published in Science in April 2012. In the 1930s, the brilliant Italian physicist Ettore Majorana deduced from quantum theory the possibility of the existence of a very special particle, a particle that is its own anti-particle. That Majorana fermion would be right on the border between matter and anti-matter. Leo Kouwenhovenʼs research group managed to create a nanoscale electronic device in which a pair of Majorana fermions ‘appear’ at either end of a nanowire. The discovery of Majorana fermions opens up a new and uncharted chapter of fundamental physics; they may also play a role in cosmology, as a proposed theory assumes that the mysterious ‘dark matter’, which forms the greatest part of the universe, is composed of Majorana fermions. Furthermore, scientists view the particles as fundamental building blocks for the quantum computer. Such a computer is far more powerful than the best supercomputer because it has the ability to be in more than one state simultaneously. Whereas digital computers require data to be encoded into binary digits (bits), quantum computation utilizes quantum properties to represent data and perform operations on these data. So far quantum computers have only existed in theory, now they may soon become a reality. In 2037 your quantum computer might record everything your patient says while simultaneously analyzing the information and comparing it with a huge memory of provings, materia medica and cured cases. By the time the interview is over and 3-D photos of the patient, DNA and all sorts of physical parameters have been entered into the equation, a differential diagnosis of homeopathic substances is proposed together with a calculation of the likelihood of a substance being the simillimum. This seems a possible scenario. Whether it would actually still involve you or whether the patient would simply run an app at home – who knows? You and homeopathy may have moved on to completely new ways of determining, creating and applying the simillimum. Practically all theoretic particles that are predicted by quantum theory have been found in the last decades, with just a few exceptions, including the enigmatic Majorana particle and the well-known Higgs boson. But Ettore Majorana the person is every bit as mysterious as the particle. In 1938 he withdrew all his money and disappeared during a boat trip from Palermo to Naples. Whether he killed himself, was murdered or lived on under a different identity is still not known. You donʼt withdraw your money and then kill yourself, do you? But then he did write what seems to be a suicide note. Was he killed by the Nazis because he refused to be involved in developing a nuclear weapon, or because they feared he might do so for the allies? Was he indeed seen in Argentina? No trace of Majorana was ever found. As if he had merged with his own anti-particle. As if he changed roles with the mysterious dark matter the particle named after him possibly explains. Could homeopathy offer an answer as to his state and possibly his fate? Itʼs tempting to at least have a look at Origanum majorana . The remedy has suicidal disposition as one of its known symptoms. The Lamiaceae are ambitious and have a great need of acknowledgement. Ettore Majorana was extremely brilliant, which would be a good way to get recognition, but theoretical physics and the sphere of action for which Origanum is known donʼt really seem to compute. Also praise may not have been an important motivation for him as he left writing a paper about another discovery he made to James Chadwick who won the Nobel Prize for it. We could analyse the books and films made about Ettore and speculate about his remedy. But we may better wait until 2037, then feed all personal writings by Ettore Majorana, his DNA and his photo into the quantum computer that he should posthumously receive a Nobel Prize for, and accept the – also posthumously – suggested remedy as his most likely simillimum. Harry van der Zee
The turn of the XXth century witnessed a revolution in physics comparable to Isaac Newton’s discovery of the universal laws of mechanics and of gravitation three centuries earlier. The world required to be described in novel terms, as the immutable, deterministic view of our familiar universe had given way to a new world picture, one which featured chance, flux, and an incessant upsurge of waves of matter. Such a worldview was so radically new and counterintuitive that it gave rise to strong debates, to the effect that Albert Einstein himself tried to oppose it on the grounds that “God does not play dice”. In spite of the intense debates that accompanied its emergence, quantum mechanics quickly proved an incredibly efficacious new tool to understand and to predict a wide array of new phenomena. It was so successful that in no time it broke free from the environment of research labs to become part of daily life, making it possible, for example, to understand why some materials were conductors, while others were insulators. Along with it, came, too, the discovery of transistors, on which much of modern electronics rests. It also led to understand how novel materials known as superconductors allow the transport of electricity with no loss, thus paving the way for new developments in the fields of medical imagery or energy distribution. Other aspects of the quantum theory led to the development of atomic clocks of astounding accuracy, which would be wrong by no more than fifteen seconds, had they been set at the beginning of the universe. A hundred years later, at the turn of the XXIst century, Quantum mechanics has lost none of its astounding power. Contemporary research has undertaken the task of exploring its less immediately perceptible aspects. Groundbreaking developments have ensued, such as the teleportation of grains of light or the possibility, once predicted by the great physicist Richard Feynman, to build, one day, novel computers which, unlike the ones we are familiar with today, will be able to process innumerable numbers of operations in parallel. The Wright Colloquium will be for us the occasion to explore, in the company of five internationallyknown specialists in the field, some of the fascinating aspects of quantum mechanics. We will appraise how efficiently quantum physics can describe our world, and confront its limitation when it is faced with the infinitely small (in relation to recent experiments carried out at the CERN) as with the incommensurably large scale of sidereal spaces. We will appreciate the extent to which quantum physics already has impacted our everyday lives, and evoke the way in which novel fields such as quantum computers and quantum information will entail profound changes in the future. The quantum adventure has only just begun! Monday 15 November 2010 - 18h30 Jochen Mannhart Center for Electronic Correlations and Magnetism, University of Augsburg, Germany Quantum Physics on the Scale of Daily Life Tuesday 16 November 2010 - 18h30 Wolfgang Ketterle Nobel Laureate 2001 (Physics), Department of Physics, Massachusetts Institute of Technology, Cambridge, U.S.A. When freezing cold is not cold enough New forms of matter close to absolute zero temperature Wednesday 17 November 2010 - 18h30 David Gross Nobel Laureate 2004 (Physics), Kavli Institute for Theoretical Physics, University of California, Santa-Barbara, U.S.A. Quantum Mechanics of the Very, Very Small and the Very, Very Large Thursday 18 November 2010 - 18h30 Alain Aspect CNRS senior scientist and Professor Institut d'Optique and Ecole Polytechnique Palaiseau, France. From Einstein’s intuition to quantum bits: a new quantum age? Vendredi 19 novembre 2010 - 18h30 Rainer Blatt Institute of Quantum Optics and Quantum Information, Austrian Academy of Sciences and University of Innsbruck, Austria The Quantum Way of Doing Computations
It was Richard Feynman who first proposed, in 1982, the far-reaching concept of \na ”quantum computer”—a device more powerful than classical computers. The idea \nof a quantum computer is to employ the fascinating and often counterintuitive \nlaws of quantum mechanics to process information. It is far from obvious that \nthe proposed concept of a quantum computer is more powerful than its classical \ncounterpart, it was only in 1994 when Peter Shor theoretically demonstrated the \nexistence of a quantum algorithm for factorizing integers into prime factors \nthat runs in polynomial time unlike its classical counterpart which works in \nsub-exponential time. The factorization of integers into prime factors is the \nbasis of asymmetric cryptography. These early theoretical results lunched an \nimmense interest of the scientific community. Already during ’90s, the first \nproposals for the physical implementation of quantum computation emerged. Ever \nsince, many experimental groups around the world pursued different physical \nimplementations of quantum bits (qubits). The first decade of the new century \nsaw a steady improvement in the control and decoherence time (the time over \nwhich the information carried by the qubit is lost) for various qubits by many \norders of magnitude. The natural next step in this context is to answer the \nquestion of how to scale the system up to include many qubits and thus build a \nquantum computer? One of the main parts of this thesis addresses exactly this \nquestion, namely the question of architecture and scalability of future quantum \ncomputer. \n \nAmong various different physical realizations of qubits, the idea of using \nelectron spins trapped in electrostatic semiconductor quantum dots as the \nbuilding blocks of a quantum computer (the so-called spin qubits), put forward \nby Daniel Loss and David DiVincenzo in 1997, triggered tremendous interest in \nscientific community. Nevertheless, the implementation of the original \nLoss-DiVincenzo proposal posed a considerable technical challenge. It used \nquantum tunneling between qubits to enable their communication with each other, \nand thus required that the qubits to be placed very close to each other. This \nrequirement not only leaves little \nspace for the placement of the vast amount of gates and wirings needed to define \nthe electrostatic quantum dots, but also makes it challenging to control the \nlocal magnetic field needed for single-qubit operations. For these reasons, no \nsystem with more than a couple of spin qubits has been \nsuccessfully implemented thus far. In the first part of this thesis, we leap \nover this long-standing problem with an entirely different strategy of using \nmetallic floating gates or ferromagnets to couple together qubits that are \nseparated over a long distance. Our scheme works for any type of \nspin qubits, including the qubits based on nitrogen-vacancy center (NV-center) \nin diamond and technologically very important silicon qubits. \n \nThe main topic of this thesis is related to quantum computer. Still, quite \nunexpectedly, some of the ideas we employed in order to tackle the problem of \nquantum computer scalability can be utilized in a completely different field of \nresearch, namely, in the field of magnetic field sensing. Qubit are not only a \nnecessary ingredient of quantum computer but they also provide a way to measure \nvery accurately magnetic fields. The magnetometer build upon the qubit based on \nNV-center, so-called NV-magnetometer, emerged in recent years as most sensitive \nmagnetic moment sensor. These magnetometers are able to detect about hundred \nnuclear spins within a minute of acquisition time. In the second part of this \nthesis, we propose an entirely novel experimental realization of \nNV-magnetometers which increases present NV-center sensitivities by four orders \nof magnitude at room temperature. This unprecedented amplification of \nsensitivity will render magnetometers capable of detecting individual nuclear \nspins. This amplification is achieved by introducing a ferromagnetic particle \nbetween the nuclear spin that needs to be detected and the NV-magnetometer. Our \nsetup, in contrast to existing schemes, is particularly advantageous because, \ndue to the large amplification of sensitivity, the nuclear spin need not lie \nwithin a few nanometers of the surface but rather can be detectable at a \ndistance of 30 nm. With these novelties, our scheme provides chemically \nsensitive spin detection under ambient conditions allowing nanoscale resolution \nof nuclear magnetic moments in biological systems—the holy grail of nuclear \nmagneticresonance. \n \nIn the last part of the thesis we focus our attention to a new direction in \nquantum computer implementation that deals with topological quantum computer \nintroduced by Alexei Kitaev in 1997; in this approach the idea is to use \nquasiparticles with ”fractional” statistics and to perform the single- and \ntwo-qubit gates by merely exchanging these quasiparticles. Additionally, \ninformation in this system is stored non-locally thus it mitigates the problem \nof decoherence caused by local noise from the environment. Majorana fermions are \none of the most well known examples of such excitations. We analyze transport \nsignatures of different topological states in one-dimensional systems, like \nMajorana fermions and fractionally charged states. We envision an Aharonov-Bohm \nsetup wherein conductance measurement provides a clear signature of presence of \nfractionally charged fermionic states, since oscillations with double period \nemerge in this case. Additionally, we propose a very simple setup that enables \nexistence of degenerate mid-gap states, so-called Tamm-Shockley states that are \ncharacterized by fractional charge and discuss possible ways of detecting these \nstates experimentally. \n
Quantum many-body systems, as they appear in different branches of physics and chemistry, are very hard to simulate. The number of parameters defining their quantum states grows exponentially with the number of constituents. This prevents us from exploring and investigating relevant problems involving relatively small numbers of subsystems even with the help of the most powerful supercomputers. Richard Feynman already noticed this difficulty back in 1981 when he wrote his visionary paper “Simulating Physics with Computers” [Int. J. Theor. Phys. 21:6/7, 467 (1982)]. There, he proposed to use quantum systems (as opposed to classical computers) to perform the simulation and in this way to circumvent the need to store and compute a colossal number of parameters, necessary to describe the pertaining superpositions. What was a visionary idea at that time has become a very active field of research in the last few years. The extraordinary progress of both theoretical and experimental research in quantum physics allows us now to tame, control, and manipulate various quantum systems with unprecedented precision. Laser, magnetic, electronic and other technologies enable us to arrange quantum subsystems in different geometries, modify their interactions, and detect them. This allows us to engineer Hamiltonians and emulate systems displaying some of the most intriguing quantum phenomena. This tremendous progress is, to a large extent, due to the pioneering work of many researchers during the last twenty to thirty years. Here, the investigations of basic phenomena with one or few atoms or photons were of particular impact. The degree of control achieved in the experiments has enabled the observation of mind-boggling quantum effects, related to the superposition principle or to entangled states, and their disappearance due to decoherence. In fact, the 2012 Nobel Prize has been awarded to two scientists, S. Haroche and D. Wineland, for such ground-breaking experiments. Such experiments, often in combination with laser cooling of atoms or ions and Bose-Einstein condensation, have formed one of the pillars on which the field of quantum simulations is being established. Quantum simulations with cold atoms, either in magnetic traps or in optical lattices, with trapped ions, with photons, with superconducting devices, with quantum dots, etc., have been theoretically proposed and experimentally considered by many researchers. Most of the proposals so far deal with problems in condensed matter physics that are either difficult to tackle with modern supercomputers or are difficult to observe in solid state systems. This has established a very close link between different disciplines, like atomic, molecular, and optical (AMO) physics, and condensed matter physics. Although some of the experiments are still in their infancy, and a lot of research is still needed, the extraordinary progress made in all these research areas during the last few years makes us feel confident that in the not too distant future quantum simulators will provide a key tool to investigate many-body quantum systems. Furthermore, we also expect that quantum simulators will help quantum physicists to establish new and fruitful links to other scientific communities, like high-energy physics or quantum chemistry. The present special issue contains various review papers as well as research papers on quantum simulations. It starts out with two papers written by last year's Nobel Prize winners describing their foundational work (Wineland, p. 739 and Haroche, p. 763). The issue continues with three thorough, invited review papers covering different topics on quantum simulations. The first one reviews recent theoretical proposals to use cold atoms in optical lattices to simulate lattice gauge theories of the sort that appear in high-energy physics (U.-J. Wiese, p. 783). The second covers both theoretical proposals and experimental demonstrations of cold-atom systems to simulate the physics of matter in the presence of gauge fields, displaying so-called topological phenomena, which so far have only been observed in solid-state systems (I. Spielman, p. 794). The third one contains an extensive overview and new proposals to perform a broad range of quantum simulations using quantum dot systems (P. Barthelmy et al., p. 813). The issue also includes six original papers with a variety of theoretical proposals as well as the introduction of novel theoretical techniques related to the field of quantum simulation. The field of quantum simulations is just starting, but we are confident that it will soon generate an even larger plethora of new ideas and discoveries, trigger interdisciplinary research, and lead us to the adventure of describing and understanding the quantum world. We hope that this special issue will help future researchers in such an exciting adventure. Rainer Blatt received his PhD degree in physics from the University of Mainz in 1981. As a postdoctoral fellow he worked on atomic beam cooling in Boulder, CO and later as a research assistant in Hamburg with single trapped ions. In 1995 he accepted a chair in experimental physics at the University of Innsbruck working on quantum information processing with trapped ions. Since 2003 he is also scientific director at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences. Immanuel Bloch received his PhD degree in physics from the Ludwig Maximilians University of Munich in 2000. As a junior group leader, he continued in Munich starting his work on ultracold quantum gases in optical lattices. In 2008 he was appointed scientific director of the newly founded division on Quantum Many-Body Systems at the Max Planck Institute of Quantum Optics. Since 2009 he also holds a chair in quantum optics at the Ludwig-Maximilians University of Munich. Ignacio Cirac received his PhD degree in physics from the Universidad Complutense de Madrid in 1991. He was professor at the Universities of Castilla-La Mancha and Innsbruck from 1991–1996 and 1996–2001, respectively. In 2001 he joined the Max-Planck Institute of Quantum Optics, where he leads the Theory Division. His current research interests include quantum information theory and quantum optics. Peter Zoller obtained his doctorate from the University of Innsbruck in 1977. He was Max Kade Fellow at the University of Southern California from 1978/79, and was JILA visiting Fellow 1981/82 and 1988. In 1990 he became JILA Fellow and professor of physics at the University of Colorado. At the end of 1994, he accepted a chair at the University of Innsbruck, where he has worked ever since. Since 2003, he has also held the position of Scientific Director at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences.
The physicists working in several areas of research know quite well the name of Ettore Majorana, since it is currently associated to fundamental concepts like {\it Majorana neutrinos} in particle physics and cosmology or {\it Majorana fermions} in condensed matter physics. But, probably, very few is known about other substantial contributions of that ingenious scholar, and even less about his personal background. For non specialists, instead, the name of Ettore Majorana is usually intimately related to the fact that he disappeared rather mysteriously on March 26, 1938, just seventy years ago, and was never seen again. The life and the work of this Italian scientist is the object of the present review, which will also offer a summary of the main results achieved in recent times by the historical and scientific researches on his work.