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Heat transfer in solids is typically conducted through either electrons or atomic vibrations known as phonons. In a vacuum, heat has long been thought to be transferred by radiation but not by phonons because of the lack of a medium.sup.1. Recent theory, however, has predicted that quantum fluctuations of electromagnetic fields could induce phonon coupling across a vacuum and thereby facilitate heat transfer.sup.2-4. Revealing this unique quantum effect experimentally would bring fundamental insights to quantum thermodynamics.sup.5 and practical implications to thermal management in nanometre-scale technologies.sup.6. Here we experimentally demonstrate heat transfer induced by quantum fluctuations between two objects separated by a vacuum gap. We use nanomechanical systems to realize strong phonon coupling through vacuum fluctuations, and observe the exchange of thermal energy between individual phonon modes. The experimental observation agrees well with our theoretical calculations and is unambiguously distinguished from other effects such as near-field radiation and electrostatic interaction. Our discovery of phonon transport through quantum fluctuations represents a previously unknown mechanism of heat transfer in addition to the conventional conduction, convection and radiation. It paves the way for the exploitation of quantum vacuum in energy transport at the nanoscale. Conventionally, heat transfer occurs by conduction, convection or radiation, but has also been theoretically predicted to occur through quantum fluctuations across a vacuum; this prediction has now been confirmed experimentally., Author(s): King Yan Fong [sup.1] , Hao-Kun Li [sup.1] , Rongkuo Zhao [sup.1] , Sui Yang [sup.1] , Yuan Wang [sup.1] , Xiang Zhang [sup.1] [sup.2] Author Affiliations: (1) Nanoscale [...]

QUANTUM MODELING FOR HIGH-ENTROPY ALLOYS Materials researchers at the DOE's Ames Laboratory, Iowa, recently identified the source of strength and ductility in high-entropy alloys (HEAs), along with ways to tune [...]

Special quantum states are used in metrology to achieve sensitivities below the limits established by classically behaving states.sup.1,2. In bosonic interferometers, squeezed states.sup.3, number states.sup.4,5 and 'Schrödinger cat' states.sup.5 have been implemented on various platforms and have demonstrated improved measurement precision over interferometers using coherent states.sup.6,7. Another metrologically useful state is an equal superposition of two eigenstates with maximally different energies; this state ideally reaches the full interferometric sensitivity allowed by quantum mechanics.sup.8,9. Here we demonstrate the enhanced sensitivity of these quantum states in the case of a harmonic oscillator. We extend an existing experimental technique.sup.10 to create number states of order up to n = 100 and to generate superpositions of a harmonic oscillator ground state and a number state of the form [Formula omitted] with n up to 18 in the motion of a single trapped ion. Although experimental imperfections prevent us from reaching the ideal Heisenberg limit, we observe enhanced sensitivity to changes in the frequency of the mechanical oscillator. This sensitivity initially increases linearly with n and reaches a maximum at n = 12, where we observe a metrological enhancement of 6.4(4) decibels (the uncertainty is one standard deviation of the mean) compared to an ideal measurement on a coherent state with the same average occupation number. Such measurements should provide improved characterization of motional decoherence, which is an important source of error in quantum information processing with trapped ions.sup.11,12. It should also be possible to use the quantum advantage from number-state superpositions to achieve precision measurements in other harmonic oscillator systems. Number-state superpositions of the harmonic motion of a trapped beryllium ion are used to measure the oscillation frequency with quantum-enhanced sensitivity, achieving a mode-frequency uncertainty of about 10.sup.-6., Author(s): Katherine C. McCormick [sup.1] [sup.2] , Jonas Keller [sup.1] , Shaun C. Burd [sup.1] [sup.2] , David J. Wineland [sup.1] [sup.2] [sup.3] , Andrew C. Wilson [sup.1] , Dietrich [...]

Atomic clocks known as optical clocks are more accurate and stable than current timekeepers. Two quantum-engineering approaches could improve the performance of optical clocks even further and extend their applications. Advances in developing a new generation of highly accurate clocks., Author(s): Christian Lisdat, Carsten Klempt Author Affiliations: Quantum engineering for optical clocks Today's most accurate clocks mark the passage of time using transitions of electrons between two energy states in [...]

We analyze von Weizsacker's view regarding the concept of information in physics. In his view, information arises from the reduction of properties of a physical object to their logical descriptive propositions. The smallest element of a lattice of propositions is an atom of information which is considered as the essence of every physical identity including position space. von Weizsacker calls this element, 'ur'. Moreover, Biological evolution is described in terms of enhancement of the variety of forms. Form could be also reduced to descriptive logical propositions, thus to atoms of information. Therefore, information is the fundamental basis in von Weizsacker's plan for unifying all branches of Physics including Chemistry and Biology. Yet, there are inadequacies in his lines of reasoning, critically assessed in this paper. Keywords Pragmatic information * Weizacker empirisist view * 'ur' theory * Biological evolution * Quantum symmetry, 1 Introduction Carl Friedrich von Weizsacker was a German philosopher and physicist whose main research activities were on nuclear fusion in the sun and other stars and on the creation [...]

Among those who make a living from the science of secrecy, worry and paranoia are just signs of professionalism. Can we protect our secrets against those who wield superior technological powers? Can we trust those who provide us with tools for protection? Can we even trust ourselves, our own freedom of choice? Recent developments in quantum cryptography show that some of these questions can be addressed and discussed in precise and operational terms, suggesting that privacy is indeed possible under surprisingly weak assumptions., Edgar Allan Poe, an American writer and an amateur cryptographer, once wrote '... it may be roundly asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve [...]

We consider an ensemble of quantum systems described by a density matrix, solution of a Lindblad-Kossakowski differential equation. We focus on the special case where the decoherence is only due to a highly unstable excited state and where the spontaneously emitted photons are measured by a photo-detector. We propose a systematic method to eliminate the fast and asymptotically stable dynamics associated with the excited state in order to obtain another differential equation for the slow part. We show that this slow differential equation is still of Lindblad-Kossakowski type, that the decoherence terms and the measured output depend explicitly on the amplitudes of quasi-resonant applied field, i.e., the control. Beside a rigorous proof of the slow/fast (adiabatic) reduction based on singular perturbation theory, we also provide a physical interpretation of the result in the context of coherence population trapping via dark states and decoherence-free subspaces. Numerical simulations illustrate the accuracy of the proposed approximation for a 5-level systems. Index Terms--Adiabatic approximation, coherent population trapping, Lindblad-Kossakowski master equation, model reduction, open quantum systems, optical pumping, singular perturbations.

The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can be applied only to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and interelectronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born--Oppenheimer approximation but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wave function is propagated on a grid with appropriately short time steps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with 100 qubits. electronic structure | quantum computation | quantum simulation

The article discusses a new distributed averaging algorithm, where in the quantized information, namely dithered quantization is employed to achieve a consensus at one of the quantization values. The expected value of the consensus is shown to be equal to the average of the original sensor data.

Energy transfer dynamics at the gas-liquid interface are examined as a function of surface temperature by using C[O.sub.2] + perfluorinated polyether (PFPE) and molecular dynamics simulations of C[O.sub.2] + fluorinated self-assembled monolayers (F-SAMs). The experiments as a function of surface temperature have disclosed an increase in both sticking probability and rotational/translational temperature of the impulsive scattering (IS) component.

A new multistate empirical valence bond model is developed for proton solvation and transport in aqueous solutions. Classical and quantum molecular dynamics simulations with the MS-EVB3 model have provided an accurate description of the solvation structure and diffusive dynamics of the excess proton.

An algorithm based on a Trotter decomposition of the quantum-classical propagator is described for simulating the quantum-classical Liouville equation. This algorithm has reproduced the exact results for stronger nonadiabatic coupling and much longer times by using fewer trajectories than other schemes for simulating quantum-classical Liouville dynamics.

Quantitative methods are used for examining the orientational order in the plastic crystal phase of apolar tetrahedral molecules. The results have shown that relaxation is nonhomogeneous in the picosecond range, with a slight dispersion of decay times depending on the initial orientational class.

The Feynman-Kleinert linearized path integral molecular dynamics (FK-LPI), ring polymer molecular dynamics (RPMD), and centroid molecular dynamics (CMD) methods are applied to the simulation of normal liquid helium. CMD has described a high-frequency component that is reduced when compared with the other methods.

Two different methods for transition-state theory (TST) rate calculations have used the notions of the moving dividing surface and the associated moving separatrices. The numerical simulations of harmonic and anharmonic systems are used for calculating reaction rates based on the reactive flux calculation by using the fixed and moving dividing surfaces.

A method is developed to form epitaxial [Ge.sub.1-x][Sn.sub.x] quantum dots (QDs) on Si(111) substrates by codeposition of Ge and Sn on ultrathin Si[O.sub.2] films with predeposited Ge nuclei. High-resolution transmission electron microscopy has shown that the main formed [Ge.sub.1-x][Sn.sub.x] QDs have less strain and no misfit dislocations.

Physical model of the defects generation leading to failure based on statistical properties for MOSFET is presented. The logistic mixture presents computational problems that are addressed in simulation.

The intrinsic properties of hypoxanthine are studied by examining the gas-phase acidity and proton affinity by using quantum mechanical calculations and gas-phase mass spectrometric methods. The acidity in gas phase is compared with that in solution and it is shown that a nonpolar environment has increased the differences in acidity among hypoxanthine, adenine and guanine.

The unsaturated D3C compounds were investigated at the molecular level using accurate quantum mechanical methods. The results indicated that the C=C double bond location imposes significant effects on the ionization potentials of D3C compounds and the inner shell binding energy spectral variations with respect to the C=C bond exhibit more site dependence.

The study results from the quantum mechanical (QM) and molecular dynamics (MD) simulations of the human antioxidant protein, HAH1, an important participant in a Cu(I) transport chain reveal preference for two- or three-coordinate exchange reaction and not the four-coordinate Cu(I) species for copper exchange.

A thorough study of the excited-state properties of the stacked dimers and trimers of 9-methyladenine in B-DNA conformation has been performed in aqueous solution by using time-dependent density functional calculations and the solvent polarizable continuum model, and results were compared with experimental results on polyadenine oligomers. The effect of base stacking on the absorption and emission spectra is fully reproduced by our calculations. Although light absorption leads to a state ([S.sub.B]) delocalized over several nucleobases, excited-state geometry optimization indicates that [S.sub.B] subsequently evolves into a state in which the excitation is localized on a single base. Analysis of the excited-state potential energy surfaces shows that [S.sub.B] can easily decay into the lowest energy excited state, [S.sub.CT], which is a dark excimer produced by intermonomer charge transfer between two stacked bases. The subpicosecond features of the time-resolved experiments are interpreted in terms of ultrafast decay from [S.sub.B]. After localization, two easy, radiationless decay channels are indeed open for [S.sub.B]: (i) ground-state recovery, according to the same mechanisms proposed for isolated adenine and/or (ii) decay to [S.sub.CT]. Our calculations suggest that the slowest part of the excited-state dynamics detected experimentally involves the [S.sub.CT] state. nucleic acid | quantum mechanics | spectroscopy | time-dependent phenomena

To evaluate the stability, potential reactivity, and relaxation mechanisms on different uraninite surfaces, surface energy values were calculated and structural relaxation was determined for the (111), (110), and (100) crystallographic faces of uranium dioxide (U[O.sub.2]) using quantum mechanical (density functional theory) and empirical potential computational methods. Quantum mechanical results are compared with empirical potential results, which use surface slab models with two different geometries, as well as various different empirical force fields. The strengths and weaknesses of the different approaches are evaluated, and surface stabilizing mechanisms such as relaxation, charge redistribution, and electronic stabilization are investigated. Quantum mechanical (q.m.) surface energy results are in agreement with the relative surface energy trends resulting from calculations using three different empirical potential sets for uranium and oxygen (two from Catlow 1977; one from Meis and Gale 1998), and with empirical force-field values published in the literature (Abramowski et al. 1999, 2001). The (111) surface consistently has the lowest surface energy (0.461 J/[m.sup.2] from q.m. calculations) and the smallest amount of surface relaxation, followed by the (110) surface (0.846 J/[m.sup.2]; q.m.), and the (100) surface (1.194 J/[m.sup.2]; q.m.) (quantum mechanical surface energy values in parentheses are for surface slabs with a thickness of four U[O.sup.2] units). Differences exist, however, in the absolute values of surface energies calculated as a function of potential set used. Quantum mechanical values are consistently lower than values calculated using empirical potential methods. A fourth potential set is presented that is derived from fitting electrostatic and short-range repulsive parameters to experimental bulk properties and surface energies and relaxations from quantum mechanical calculations. Keywords: Uraninite, U[O.sup.2], surface energy, quantum mechanical, empirical potentials, force fields, uranium dioxide

Progress in science is inextricably linked with how well we can observe the world around us. It is by making increasingly better measurements that scientific theories are tested and refined. In this article we address the question of what the ultimate limit to measurement precision is and how it could be achieved in the laboratory. We focus on how, by making use of quantum theory, it is possible to make better measurements than anything that can be achieved with classical techniques. This opens the door to an array of new technologies and could help answer some of science's most engaging questions.

We present a pedagogical treatment of the formalism of continuous quantum measurement. Our aim is to show the reader how the equations describing such measurements are derived and manipulated in a direct manner. We also give elementary background material for those new to measurement theory, and describe further various aspects of continuous measurements that should be helpful to those wanting to use such measurements in applications. Specifically, we use the simple and direct approach of generalized measurements to derive the stochastic master equation describing the continuous measurements of observables, give a tutorial on stochastic calculus, treat multiple observers and inefficient detection, examine a general form of the measurement master equation, and show how the master equation leads to information gain and disturbance. To conclude, we give a detailed treatment of imaging the resonance fluorescence from a single atom as a concrete example of how a continuous position measurement arises in a physical system.

Quantum annealing is a promising tool for solving optimization problems, similar in some ways to the traditional (classical) simulated annealing of Kirkpatrick et al. Simulated annealing takes advantage of thermal fluctuations in order to explore the optimization landscape of the problem at hand, whereas quantum annealing employs quantum fluctuations. Intriguingly, quantum annealing has been proved to be more effective than its classical counterpart in many applications. We illustrate the theory and the practical implementation of both classical and quantum annealing--highlighting the crucial differences between these two methods by means of results recently obtained in experiments, in simple toy-models, and more challenging combinatorial optimization problems (namely, Random Ising model and Travelling Salesman Problem). The techniques used to implement quantum and classical annealing are either deterministic evolutions, for the simplest models, or Monte Carlo approaches, for harder optimization tasks. We discuss the pro and cons of these approaches and their possible connections to the landscape of the problem addressed.

The mechanism of DNA cytosine-5-methylation catalyzed by the bacterial M.Hhal enzyme has been considered as a stepwise nucleophilic addition of Cys-81-[S.sup.-] to cytosine C6 followed by C5 nucleophilic replacement of the methyl of S-adenosyl-L-methionine to produce 5-methyl-6-Cys-81-S-5,6-dihydrocytosine. In this study, we show that the reaction is concerted from a series of energy calculations by using the quantum mechanical/molecular mechanical hybrid method. Deprotonation of 5-methyl-6-Cys-81-S-5,6-dihydrocytosine and expulsion of Cys-81-S provides the product DNA 5-methylcytosine. A required base catalyst for this deprotonation is not available as a member of the active site structure. A water channel between the active site and bulk water allows entrance of solvent to the active site. Hydroxide at [10.sup.-7] mole fraction (pH = 7) is shown to be sufficient for the required catalysis. We also show that Glu-119-C[O.sub.2]H can divert the reaction by protonating cytosine N3 when Cys-81-S- attacks cytosine, to form the 6-Cys-81-S-3-hydrocytosine. The reactants and 6-Cys-81-S-3-hydrocytosine product are in rapid equilibrium, and this explains the observed hydrogen exchange of cytosine with solvent. computational

Byline: Ramon Carbo-Dorca (1,2) Keywords: Einstein--Podolski--Rosen paradox; wavefunction structure; expectation values; inward matrix product; selectors Abstract: A unique wavefunction, constructed according to the original Einstein--Podolski--Rosen (EPR) description, is used here to analyze the behavior of two equal non-interacting quantum systems: S(1) and S(2).The results show that the EPR paradox, which will be referred as EPR effect in this work, always appears in this theoretical context. When the expectation value of a Hermitian operator is sought, it can yield two different values, when measured on S(1) or S(2). However, the EPR effect disappears if the wavefunction is chosen symmetric or antisymmetric by interchanging the S(1) and S(2) coordinates. The same EPR effect appears when the expectation value of a state selector projection operator is computed on S(1) or S(2), but it disappears within a symmetric or antisymmetric EPR wavefunction form. On the other hand, the action of the selectors over the EPR wavefunction provide images on EPR system S(1) or S(2) which could be different, so the EPR effect persists except if, similarly as in the statistical case, a wavefunction constructed with a symmetric or antisymmetric superposition with respect the EPR system coordinates is used. Thus, with appropriate wavefunction choices, in statistical expectation value measures and non-statistical selector images as well, the EPR effect could not persist. Author Affiliation: (1) Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281, B-9000, Gent, Belgium (2) Institut de Quimica Computacional, Universitat de Girona, Girona, 17071, Catalonia, Spain Article History: Registration Date: 21/10/2005 Received Date: 07/06/2005 Online Date: 23/12/2005 Article note: *This second paper on EPR paradox is also expressly dedicated to the memory Professor Einstein, in order to celebrate the 100th anniversary of the first paper on relativity theory, but also to commemorate the 75 anniversary of the publication of EPR paradox, thus, as before, Professors Podolski and Rosen are also included in the homage.

Byline: Gustavo A. Arteca (1,2), O. Tapia (3) Keywords: diabatic functions; reaction rates; transition states; quantum states; external fields Abstract: The method discussed in this work provides a theoretical framework where simple chemical reactions resemble any other standard quantum process, i.e., a transition in quantum state mediated by the electromagnetic field. In our approach, quantum states are represented as a superposition of electronic diabatic basis functions, whose amplitudes can be modulated by the field and by the external control of nuclear configurations. Using a one-dimensional three-state model system, we show how chemical structure and dynamics can be represented in terms of these control parameters, and propose an algorithm to compute the reaction probabilities. Our analysis of effective energy barriers generalizes previous ideas on structural similarity between reactant, and product, and transition states using the geometry of conventional reaction paths. In the present context, exceptions to empirical rules such as the Hammond postulate appear as effects induced by the environment that supplies the external field acting on the quantum system. Author Affiliation: (1) Deepartement de Chimie et Biochimie, Laurentian University, Ramsey Lake Road, Sudbury, Ontario (2) Canada P3E 2C6 and Department of Physical Chemistry, Uppsala University, Box 579, S-751 23, Uppsala, Sweden (3) Department of Physical Chemistry, Uppsala University, Box 579, S-751 23, Uppsala, Sweden Article History: Registration Date: 03/12/2004 Received Date: 04/09/2004

A quantum mechanical investigation of the nucleophilic addition to the cyclopropane ring of a representative member of antitumor antibiotics related to CC-1065 is presented. The results are in agreement with the experimental trends and suggest that, contrary to methanol, N-base can be effective also under neutral conditions, irrespective of the additional steric constraints experienced in the biologically active substrate (DNA).

Researchers are expected to see the minute-by-minute activities of cancer cell, with a new technology that uses fluorescent inorganic nanocrystals that glow under UV light. The study included quantum dots in conjunction with mutiphoton and emission scanning microscopy in which each dot emits a different color from blue to infrared, which helps the researcher to identify each of five populations of tumor cells.