Showing papers in "Contemporary Physics in 2007"
TL;DR: A spin chain is a permanently coupled 1D system of spins as discussed by the authors, which can be used to connect quantum registers without resorting to optics, and it has been shown that it is possible to achieve perfect quantum state transfer through spin chains.
Abstract: We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
439 citations
TL;DR: In this article, the authors present a theoretical study on the temperature and the composition of the Earth's core, based on the application of the quantum mechanics known as density functional theory, which can be usefully used to study the properties of the core.
Abstract: The Earth's core is a ball of swirling hot metal at the centre of our planet, with a radius roughly one half of the Earth's radius. It is formed by two parts: a solid inner core, with a radius of 1221 km, surrounded by a shell of liquid which extends up to 3480 km from the centre. It is widely believe that the Earth's core is mainly formed by iron, or iron with up to 5-10% of nickel. It is also known that the core must contain a significant fraction of light impurities, in the region of 2-3% in the solid and 6-7% in the liquid. The nature of these light impurities is unknown. The temperature of the core is also inaccessible to direct probing. Here we present a theoretical study on the temperature and the composition of the Earth's core. The investigation is based on the application of the implementation of quantum mechanics known as density functional theory. We shall show that these techniques are very accurate at predicting the properties of iron, and therefore can be usefully used to study the properties of the core. We show that by combining these techniques with direct observations it is possible to predict the temperature of the core, in particular the temperature at the boundary between the solid and the liquid core (the ICB), and put constraints on its composition. The result of this study is that the temperature of the ICB is probably in the region of 5400-5700 K and that the outer core contains a significant fraction (8-13%) of oxygen. As the Earth cools down the solid core grows and expels oxygen in the liquid. Since oxygen is lighter than iron it rises in the liquid, and its gravitational energy is available to drive the convective motions in the liquid core that are responsible for the generation of the Earth's magnetic field.
96 citations
TL;DR: The computational realizations of the test null hypothesis known as the surrogate data are introduced within the context of discerning nonlinear dynamics from noise, and the concept is further generalized for detection of directional interactions, or causality in bivariate time series.
Abstract: Principles and applications of statistical testing as a tool for inference of underlying mechanisms from experimental time series are discussed. The computational realizations of the test null hypothesis known as the surrogate data are introduced within the context of discerning nonlinear dynamics from noise, and discussed in examples of testing for nonlinearity in atmospheric dynamics, solar cycle and brain signals. The concept is further generalized for detection of directional interactions, or causality in bivariate time series.
75 citations
TL;DR: In this article, the magnetic properties of windblown dust and interbedded soil layers of the Chinese Loess Plateau are used to calculate rainfall for the last million years, identifying the waxing and waning of the Southeast Asian summer monsoon.
Abstract: A major and pressing problem is to understand how, and how fast, the Earth's climate has changed in the past, with and without human influences on the global carbon cycle. Magnetic, remanence-acquiring, minerals, mostly iron oxides and sulphides, occur ubiquitously in sediments. They can act as sensitive recorders of past climates, because as climate has varied (from glacial to interglacial, for example), the mineralogy, magnetic domain state, composition and source of these minerals has varied. Here, the magnetic properties of windblown dust and interbedded soil layers of the Chinese Loess Plateau are used to calculate rainfall for the last million years, identifying the waxing and waning of the Southeast Asian summer monsoon. Comparison of our magnetic rainfall record on land with environmental records from the deep-sea shows that summer monsoon intensity is linked with growth and decay of continental-sized ice sheets, in turn reflecting changes in the Earth's orbit around the Sun.
71 citations
TL;DR: In this paper, the authors use the detection method used for the quantum state characterization to identify the quantum states by studying its uncertainties of its field amplitude and phase properties which correspond to conjugate quantum observables.
Abstract: The quantization of light is the basis for quantum optics and has led to the observation of a multitude of genuine quantum effects which cannot be explained by classical physics. Yet, there exist different views when we refer to the distinct quantum character of light as opposed to classical fields. A major impact on how we describe photonic states is caused by the detection method we use for the quantum state characterization. In the theoretical modelling measuring light always means the recording of photon statistics of some kind, though the way we interpret the results is quite different and depends mainly on the intensity of actual detected light. If we use conventional photodiodes and monitor bright light, we attribute the detected statistics to quadrature measurements in a phase space representation, or—in other words—we identify the quantum state by studying its uncertainties of its field amplitude and phase properties which correspond to conjugate quantum observables. For multi-photon states with ...
67 citations
TL;DR: In this article, it was shown that the thermal radiation of a large number of substances is coherent, both in space and time, when it is observed at a distance from the body that is shorter than the wavelength.
Abstract: The radiation emitted by a heated body is generally quoted as a typical example of incoherent radiation, in distinction to laser radiation. One is nearly isotropic, the other highly directional; one is spectrally broad, the other quasi-monochromatic. It may come as a surprise that the thermal radiation of a large number of substances is coherent, both in space and time, when it is observed at a distance from the body that is shorter than the wavelength. This behaviour can be understood within an electromagnetic approach to thermal emission. Several recent experiments have confirmed these unexpected properties.
34 citations
TL;DR: This work provides an exhaustive account of the reasons of enormous relevance underlying the protein folding problem and summarize the present-day status of the methods aimed at solving it, and physically defines the problem stating the assumptions behind this (commonly implicit) definition.
Abstract: The prediction of the three-dimensional native structure of proteins from the knowledge of their amino acid sequence, known as the protein folding problem, is one of the most important yet unsolved issues of modern science. Since the conformational behaviour of flexible molecules is nothing more than a complex physical problem, increasingly more physicists are moving into the study of protein systems, bringing with them powerful mathematical and computational tools, as well as the sharp intuition and deep images inherent to the physics discipline. This work attempts to facilitate the first steps of such a transition. In order to achieve this goal, we provide an exhaustive account of the reasons of enormous relevance underlying the protein folding problem and summarize the present-day status of the methods aimed at solving it. We also provide an introduction to the particular structure of these biological heteropolymers, and we physically define the problem stating the assumptions behind this (commonly imp...
31 citations
TL;DR: The Pioneer 10 and 11 missions were the first to explore the outer solar system and achieved stunning breakthroughs in deep-space exploration as discussed by the authors. But beginning in about 1980 an unmodelled force of ∼8×10−8 cm−s−2, directed approximately towards the Sun, appeared in the tracking signal.
Abstract: In 1972 and 1973 the Pioneer 10 and 11 missions were launched. They were the first to explore the outer solar system and achieved stunning breakthroughs in deep-space exploration. But beginning in about 1980 an unmodelled force of ∼8×10−8 cm s−2, directed approximately towards the Sun, appeared in the tracking signal. It later was unambiguously verified as being in the data and not an artefact. The cause remains unknown (although radiant heat remains a likely origin). With time more and more effort has gone into understanding this anomaly (and also possibly related effects). We review the situation and describe ongoing programmes to resolve the issue.
27 citations
TL;DR: In this paper, a phase space distribution called the Kirkwood-Rihaczek (KR) distribution has been proposed to explain the nonlinear evolution of a Gaussian wave packet in an infinite potential well, leading to fractional revivals of the initial wave packet.
Abstract: The nonlinear evolution of certain quantum systems such as a Gaussian wave packet in an infinite potential well, can lead to fractional revivals of the initial wave packet. Analogously, a coherent state propagating through a Kerr medium can form the so-called Schrodinger cats and cat-like states. Recently, it was shown that a superposition of Schrodinger cats can give rise to sub-Planck structures in the Wigner distribution. The purpose of this review is to introduce and apply, in the above context, a phase space distribution ‘which differs but little from Wigner's and yet, had remained obscure for decades. This is the Kirkwood – Rihaczek (KR) distribution, which has aroused considerable interest in recent years. It is thus appropriate and timely to see how it compares with the Wigner distribution in analysing the above phenomena. Our detailed analysis shows that the KR distribution is just as adequate in explaining these phenomena as the Wigner distribution. Sub-Planck structures are obtained in the KR d...
16 citations
TL;DR: The Large Hadron Collider (LHC) as discussed by the authors is a 7 {circle plus} 7 TeV proton-proton collider under construction at CERN (the European Laboratory for Particle Physics in Geneva), where mysteries of the electroweak interaction will be unveiled.
Abstract: The Large Hadron Collider, a 7 {circle_plus} 7 TeV proton-proton collider under construction at CERN (the European Laboratory for Particle Physics in Geneva), will take experiments squarely into a new energy domain where mysteries of the electroweak interaction will be unveiled. What marks the 1-TeV scale as an important target? Why is understanding how the electroweak symmetry is hidden important to our conception of the world around us? What expectations do we have for the agent that hides the electroweak symmetry? Why do particle physicists anticipate a great harvest of discoveries within reach of the LHC?
10 citations
TL;DR: In this article, the relevance of electron-lattice coupling and the resulting Jahn-Teller polaron is elaborated, and the general features of electronic phase separation, which results from disorder and strain effects, are discussed along with electron lattice coupling effects.
Abstract: In this article, we review the insulator–metal transition and the colossal magnetoresistance effect in manganites. The relevance of electron–lattice coupling and the resulting Jahn–Teller polaron is elaborated. The general features of electronic phase separation, which results from disorder and strain effects, are discussed along with electron–lattice coupling effects. Although a comprehensive theory is still lacking that can account for all the intricate features of manganite physics, electronic-phase separation and electron–lattice coupling appear to capture the essence of the colossal magnetoresistance effect in manganites.
TL;DR: Kim and Chan as mentioned in this paper showed that solid 4He is indeed a supersolid solid, a super-fluid solid that can flow like a liquid and even without friction like a superfluid.
Abstract: Is it possible that a solid flows like a liquid, or even without friction like a superfluid? At first sight, the crystalline order in real space looks contradictory with the coherent motion which is responsible for superfluidity. However, several authors considered this possibility in 1969 – 1970, and experiments done by Kim and Chan in 2004 suggest that solid 4He is indeed a superfluid solid—a ‘supersolid’—below about 100 mK. This article summarizes my present understanding of this paradoxical issue.
TL;DR: The recent discoveries of planetary systems in orbit around other stars have uncovered several types of planetary objects which are not represented in our own solar system as mentioned in this paper. But these types of objects do not fall into the gap between the masses of Earth and Neptune.
Abstract: The recent discoveries of planetary systems in orbit around other stars have uncovered several types of planetary objects which are not represented in our own solar system. In addition to the well known ‘hot-Jupiters’—gas giant planets at very short orbital distances from their parent stars—recent observations have discovered Neptune-mass objects in short-period orbits, as well as planets which appear to fall squarely into the gap between the masses of Earth and Neptune. In this paper we review the observations of these fascinating new objects, and discuss theories of their formation and speculations on their possible interior structures.
TL;DR: Segre as discussed by the authors reviews Faust in Copenhagen, by G. Segre, Jonathan Cape, London, 2007, pp. 320, £20.00, $25.95, hardback (ISBN 9780224072564).
Abstract: Reviews of Faust in Copenhagen, by G. Segre, Jonathan Cape, London, 2007, pp. 320, £20.00, $25.95, hardback (ISBN 9780224072564). Scope: history of modern physics. Level: undergraduate. Uncertainty...
TL;DR: In a little over three years major new progress has been made in the study of gauge theories and gravity, using ideas inspired by twistor string theory as discussed by the authors, which have ranged from new, unexpected reformulations and reorganizations of these theories, to novel, highly efficient techniques for calculating physical scattering amplitudes in theories such as QCD.
Abstract: In a little over three years major new progress has been made in the study of gauge theories and gravity, using ideas inspired by twistor string theory. These have ranged from new, unexpected reformulations and reorganizations of these theories, to novel, highly efficient techniques for calculating physical scattering amplitudes in theories such as QCD. We review these developments here, and discuss the latest areas of research in the field.
TL;DR: In this paper, a short introduction to Helmholtz's theory of musical harmony is given, which explains why a perfect fifth sounds consonant yet a diminished fifth is dissonant.
Abstract: Can science reveal the secrets of music? This article addresses the question with a short introduction to Helmholtz's theory of musical harmony It begins by discussing what happens when tones are played at the same time, which introduces us to the idea of beats Next, the difference between a pure tone and a note played on an instrument is explained, which provides the insight needed to form Helmholtz's theory This allows us to explain why a perfect fifth sounds consonant yet a diminished fifth is dissonant
TL;DR: The Tragic Intellect by Thorpe as discussed by the authors is a sociological account of Oppenheimer's political rise and fall in the context of the militarization of science and the ethical tensions between the scientist, as simple provider of gadgets, and the scientist as a uniquely informed and perhaps morally sound, governmental insider.
Abstract: Unlike all the other wartime combatants, who had been economically ruined and psychologically scarred, America emerged from the war in 1945 as the self-confident, totally dominant world power both economically, commanding 50% of world trade and militarily as the only nation with an atom bomb. Clearly a much needed, safer new world order was in her gift, if she had had the will. There was a slim chance to ban nuclear weapons and openly share nuclear technology for the benefit of man. There was a chance to use the wartime alliance to heal the festering international antagonism between socialism and capitalism. The Oppenheimer myth castes the man as both the ‘father of the atom bomb’ and the deeply concerned humanist, who strove valiantly to have America take these opportunities. The myth attributes his ultimate failure to the total intransigence of the Soviet Union and that now familiar hawkish American clique, hell bent on using its military power to maintain a dominant world position, by preventative war if needs be. Oppenheimer: The Tragic Intellect is a ‘sociological biography’, the second recent addition to an ever expanding library of Oppenheimer studies that began with Jungk’s book in 1958 [1]. Thorpe’s new book was shortly preceded by American Prometheus co-authored by Sherwin and Bird [2]. Both these new studies follow very similar lines, but this later one has a slightly wider reach, seeking to place Oppenheimer’s political rise and fall in the sociological context of the militarization of science and the ethical tensions between the scientist, as simple provider of gadgets, and the scientist as a uniquely informed and perhaps morally sound, governmental insider. Thorpe traces Oppenheimer’s private and academic life from childhood and schooling in New York, through Harvard in the early 1920s, his painful year in the Cavendish, winning his theoretical spurs in Gottingen, under Born, and then back to Berkeley and then in 1942 to Los Alamos. On the back of the fame, or was it infamy, attached to the nuclear devastation of Hiroshima and Nagasaki, Oppenheimer becomes a celebrity and a very influential scientific advisor, ‘insider’ to the Truman and Eisenhower administrations until 1954 when quite unfairly he is hounded from his insider status at a show trial, concocted by Lewis Strauss, an arch enemy, under the auspices of the AEC personnel department. In this history, Thorpe seeks the personality fragments, which perhaps made up the man who became so utterly confusing an icon after 1945. Whereas his leadership of the Los Alamos laboratory between 1942 and 1945 earns almost universal praise, his subsequent apparent twists and turns of position on nuclear weapons, left many scientists, who had worked under him during the wartime project, feeling betrayed. Thorpe seems to suggest that betrayals, both little and large, were recurring events in Oppenheimer’s private and public life. At face value there is a need to explain his rapid transition (yet another apparent betrayal?), from deeply concerned, moral scientist in 1945 to the nuclear insider, quite ready to defend at least the central parts of the nuclear policies of both the Truman and Eisenhower administrations. Possibly he came to believe that he and he alone, using his international celebrity status as ‘father of the atom bomb’, could rein in the American administration. Both Thorpe and Sherwin take a simpler view. Broadly speaking, Oppenheimer simply acquired a taste for