Showing papers on "Quantum published in 1986"
TL;DR: The physical limitations due to quantum mechanics on the functioning of computers are analyzed in this paper, where the physical limitations of quantum mechanics are discussed and the physical limits of quantum computing are analyzed.
Abstract: The physical limitations, due to quantum mechanics, on the functioning of computers are analyzed.
1,717 citations
TL;DR: In this paper, a general review of experimental work is presented in order to permit a comprehensive evaluation of current understanding of the quantum size effect on the electronic spectrum including magnetic susceptibility, nuclear magnetic resonance, electron spin resonance, heat capacity, optical, and infrared absorption measurements.
Abstract: The subject of small metallic particle properties is outlined with emphasis on quantum electronic effects. The theoretical background for interpretation of experiments is discussed beginning with the work of Kubo. More recent amendments to this have been included, taking into account the techniques of random matrix theory and effects of the spin-orbit interaction. A general review of experimental work is presented in order to permit a comprehensive evaluation of current understanding of the quantum size effect on the electronic spectrum. This survey includes magnetic susceptibility, nuclear magnetic resonance, electron spin resonance, heat capacity, optical, and infrared absorption measurements. These are discussed in many instances from the point of view of there being competing size effects arising from a reduced volume contrasted with those from the surface. A number of stimulating and provocative results have led to the development of new areas of research involving metallic clusters such as cluster beam techniques, far-infrared absorption by particle clusters, adsorbate NMR, and particle-matrix composites. Although there is little question that the experiments themselves indicate the existence of quantum effects, there are as yet, insufficient results to test the theoretical predictions for electron-level distribution functions based on fundamental symmetries of the electron Hamiltonian. A new suggestion for measurement of the electron-level correlation function is made using the magnetic field dependence of the NMR Knight shift. Particle preparation methods are also reviewed with commentary on the problems and advantages of these techniques for investigation of quantum electronic effects.
1,153 citations
TL;DR: The direct observation of quantum jumps between the 6-2 and 5-2 states is demonstrated, and the resulting ``telegraph signal'' provides a direct monitor of the atomic state.
Abstract: We demonstrate here the direct observation of quantum jumps between the ${6}^{2}$${\mathrm{S}}_{1/2}$ state and the ${5}^{2}$${\mathrm{D}}_{5/2}$ state of an individual laser-cooled ${\mathrm{Ba}}^{+}$ ions contained in a radio-frequency trap. The state detection and cooling are performed by two lasers which cause ${6}^{2}$${\mathrm{S}}_{1/2}$${\mathrm{\ensuremath{-}}6}^{2}$${\mathrm{P}}_{1/2}$${\mathrm{\ensuremath{-}}5}^{2}$ ${\mathrm{D}}_{3/2}$ transitions. Incoherent excitation to the ${5}^{2}$${\mathrm{D}}_{5/2}$ state (via the ${6}^{2}$${\mathrm{P}}_{3/2}$ level) causes the fluorescence from the ${6}^{2}$${\mathrm{P}}_{1/2}$ state to be suppressed for g30-sec lifetime of that state, after which the fluorescence reappears. The resulting ``telegraph signal'' provides a direct monitor of the atomic state.
719 citations
TL;DR: In this article, a two-photon or multiphoton process that is resonant with an excited electronic state can be used to assist chemistry on the ground state potential energy surface by controlling the delay between a pair of ultrashort (femtosecond) laser pulses.
Abstract: We present a novel approach to the control of selectivity of reaction products The central idea is that in a two‐photon or multiphoton process that is resonant with an excited electronic state, the resonant excited state potential energy surface can be used to assist chemistry on the ground state potential energy surface By controlling the delay between a pair of ultrashort (femtosecond) laser pulses, it is possible to control the propagation time on the excited state potential energy surface Different propagation times, in turn, can be used to generate different chemical products There are many cases for which selectivity of product formation should be possible using this scheme We illustrate the methodology with numerical application to a variety of model two degree of freedom systems with two inequivalent exit channels Branching ratios obtained using a swarm of classical trajectories are in good qualitative agreement with full quantum mechanical calculations
604 citations
Book•
01 Jan 1986
TL;DR: A conference held in Oxford in the spring of 1984 to discuss quantum gravity and general relativity is described in this paper, which brings together contributors who examine different aspects of the problem, including experimental support for quantum mechanics, its strange and apparently paradoxical features, its underlying philosophy, and possible modifications to the theory.
Abstract: Recent developments in quantum theory have focused attention on fundamental questions, in particular on whether it might be necessary to modify quantum mechanics to reconcile quantum gravity and general relativity This book is based on a conference held in Oxford in the spring of 1984 to discuss quantum gravity It brings together contributors who examine different aspects of the problem, including the experimental support for quantum mechanics, its strange and apparently paradoxical features, its underlying philosophy, and possible modifications to the theory
458 citations
TL;DR: In this article, non-abelian bosonization is used to predict critical exponents for quantum chains of arbitrary spin and arbitrary symmetry SU(n), passing to the large representation limit gives non-linear σ-models on the manifolds U(2n)/U(n)×U (n) at topological angle θ=π.
351 citations
TL;DR: In this article, a theory of weak localization which is put rigorously on a quasiclassical basis is presented, and all the important quantitative results obtained so far are recovered.
295 citations
TL;DR: It is demonstrated that the revivals of atomic excitation which are the signature of the quantum nature of the evolution are strongly affected by field dissipation even when the damping hardly affects the underlying Rabi oscillations.
Abstract: The fully quantum-electrodynamical model of a two-level atom interacting with a single-cavity mode predicts an atomic evolution whose form is dictated by the discrete nature of the field energy and its statistical distribution. We demonstrate that the revivals of atomic excitation which are the signature of the quantum nature of the evolution are strongly affected by field dissipation even when the damping hardly affects the underlying Rabi oscillations.
212 citations
TL;DR: In this article, the first 3D reactive scattering calculations using symmetrized hyper-spherical coordinates (SHC) were performed for a significantly large number of systems than has heretofore been possible.
Abstract: We report here the first three-dimensional (3D) reactive scattering calculations using symmetrized hyper-spherical coordinates (SHC). They show that the 3D local hyper-spherical surface function basis set leads to a very efficient computational scheme which should permit accurate reactive scattering calculations to be performed for a significantly large number of systems than has heretofore been possible.
156 citations
IBM1
TL;DR: In an optical fiber, nonlinear optical interactions couple the sideband modes of two strong pump waves at different frequencies just as required for a quantum non-demolition measurement as discussed by the authors.
Abstract: In an optical fiber, nonlinear optical interactions couple the sideband modes of two strong pump waves at different frequencies just as required for a quantum nondemolition measurement. Experimental measurements demonstrate that 37% of the rms phase fluctuations of one wave are caused by the quantum amplitude fluctuations of the other.
141 citations
TL;DR: In this article, the authors show that for a system staying in thermal equilibrium with its environment, this hypothesis leads to a violation of the KMS condition, the fluctuation dissipation theorem, and under certain conditions to a fundamental principle of detailed balancing.
TL;DR: In this article, a model involving quasi-elastic inter-Landau-level scattering is proposed to explain the three main features of recent experiments by Bliek and co-workers on the dissipative transverse magnetoresistance of the two-dimensional electron gas in GaAs/(AlGa)As heterostructures in which there is a narrow constriction in the conducting channel.
Abstract: A model involving quasi-elastic inter-Landau-level scattering is proposed to explain the three main features of recent experiments by Bliek and co-workers on the dissipative transverse magnetoresistance of the two-dimensional electron gas in GaAs/(AlGa)As heterostructures in which there is a narrow constriction in the conducting channel. These features are the high breakdown current densities observed, the magnetic field values of the 'quantum' steps in the magnetoresistance and the quantised values of the magnetoresistance.
TL;DR: It is found that by a tuning of Planck's constant, the statistics of the quasienergy spectrum go continuously from showing Poisson to Gaussian-orthogonal-ensemble-like properties.
Abstract: We consider the problem of a free particle in a rigid box with one wall fixed and the other oscillating periodically in time. The spectral properties of the evolution operator are calculated. We find that by a tuning of Planck's constant, the statistics of the quasienergy spectrum go continuously from showing Poisson to Gaussian-orthogonal-ensemble-like properties. This change is related to a transition from localized to extended states in energy space. We make the conjecture that recent results of microwave excitations on quasi one-dimensional highly excited hydrogen atoms may be related to this work.
TL;DR: In this article, the first results for quantum mechanical calculations of chemical reaction probabilities are presented, which involves the expansion of the amplitude density due to the difference between the true interaction potential and a distortion potential in a square integrable basis set and the solution of a large set of coupled equations for the basis function coefficients.
Abstract: The first results of a new method for quantum mechanical calculations of chemical reaction probabilities are presented. The method involves the expansion of the amplitude density due to the difference between the true interaction potential and a distortion potential in a square integrable basis set and the solution of a large set of coupled equations for the basis function coefficients. They find a threshold energy for D + H/sub 2/(upsilon = 1) ..cap alpha.. HD + H, where upsilon is the vibrational quantum number, in good agreement with previous semiclassical tunneling calculations.
TL;DR: In this paper, it was shown that the usual master equation formalism of markovian open quantum systems is completely equivalent to a certain state vector formalism, where the state vector of the system satisfies a given frictional Schrodinger equation except for random instant transitions of discrete nature.
TL;DR: The evolution of quantum fields in theories with relatively flat potentials is considered in this paper, where it is shown that bubble nucleation, a quantum mechanical tunneling process, may occur even if V(φ) has no barrier.
TL;DR: On donne des exemples de mecanique quantique dans lesquels la phase de Beny donne naissance a des termes de Wess-Zumino avec l'approximation de Born-Oppenheimer.
Abstract: I provide some simple quantum-mechanical examples in which the Berry phase gives rise to Wess-Zumino terms. The connection with the Born-Oppenheimer approximation is also discussed.
TL;DR: A general formula for soliton form factors of several local fields in the quantum sine-Gordon model is presented in this article, which is a generalization of the soliton soliton formula presented in this paper.
Abstract: A general formula for soliton form factors of several local fields in the quantum sine-Gordon model is presented.
TL;DR: The quantum theory of activated events in condensed phases, developed by Wolynes using path integral techniques, was derived via harmonic quantum state theory as discussed by the authors, which is derived via path integral technique.
TL;DR: Etablissement d'un fonctionnelle generatrice de translations invariante par rotation pour le modele continu d'une chaine ferromagnetique; la condition d'invariance par rotation mene a une quantification topologique.
Abstract: A rotationally invariant translation-generating functional for the continuum model of a ferromagnetic chain is found, resolving a long-standing paradox. The condition of rotational invariance leads to a topological quantization in the continuum classical model that corresponds to spin quantization in the equivalent discrete quantum model. The relation between the classical continuum model and the discrete quantum models is made precise.
TL;DR: In this paper, the authors present a method of obtaining exact isolated solutions for the class of quantum optical systems without the use of a rotating wave approximation, which generalises the results known from the literature to the case of multilevel atomic systems.
Abstract: The authors present a method of obtaining exact isolated solutions for the class of quantum optical systems without the use of a rotating wave approximation. The method generalises the results known from the literature to the case of multilevel atomic systems. The analytical properties of the solutions in the Bargmann representation for the radiation field mode are discussed. The analogues of these solutions for atomic systems interacting with an external field are constructed.
TL;DR: In this article, it is shown that the wavefunctions take a particularly simple form when the number of coupled modes is less than or equal to two, and the correspondence between classical and quantum descriptions of a local mode is also considered.
TL;DR: Semiclassical theory provides a useful picture of quantum features (interference in product state distribution, generalized tunneling phenomena, and others) in these more complex systems.
Abstract: Semiclassical theory finds use in chemical physics both as a computational method and as a conceptual framework for interpreting quantum features in experiments and in numerical quantum calculations. The semiclassical description of one-dimensional dynamical systems is essentially a solved problem for eigenvalue and scattering situations and for general topologies of potential functions (simple potential wells, multiple wells, multiple barriers, and so forth). Considerable progress has also been made in generalizing semiclassical theory to multidimensional dynamical systems (such as inelastic and reactive scattering of atoms and molecules and vibrational energy levels of polyatomic molecules), and here, too, it provides a useful picture of quantum features (interference in product state distribution, generalized tunneling phenomena, and others) in these more complex systems.
TL;DR: C coupled dynamical equations for both energy levels and eigenfunctions with a nonintegrability parameter $t$ taken as "time" are shown to be a completely integrable Calogero-Moser system in 1 + 1 dimensions with internal complex vector space.
Abstract: For quantum bound systems whose classical versions are nonintegrable, coupled dynamical equations for both energy levels and eigenfunctions with a nonintegrability parameter $t$ taken as "time" are shown to be a completely integrable Calogero-Moser system in 1 + 1 dimensions with internal complex vector space. Lax forms and their complete algebraic solutions are given which, in place of statistical mechanics procedures, determine possible energy spectrum and wave-function patterns at an arbitrary value of $t$.
TL;DR: In this paper, a new quantum transition-state theory is defined by using the reactive flux correlation function of Miller, Schwartz, and Tromp (J. Chem. Phys. 1983, 79, 4889).
Abstract: Classical transition-state theory is based on the direct, short-time (actually, zero time) classical dynamics through a dividing surface that separates reactants and products. This paper defines a new quantum mechanical version of transition-state theory by using the reactive flux correlation function of Miller, Schwartz, and Tromp (J. Chem. Phys. 1983, 79, 4889) to identify the short-time quantum dynamics through the dividing surface. It is seen that short time quantum mechanically is not zero time, as it is classically, but rather a time of order Planck's constant..beta... This new quantum version of transition-state theory is also seen to have some of the variational character of the classical case. Finally, it is shown how the reactive flux correlation function of Miller, Schwartz, and Tromp can be generalized by choosing various forms of the projector onto reactants, and this is seen to have important consequences for the accuracy of this new quantum transition-state theory.
TL;DR: In this article, a quantum analogue of the classical transformations to the Birkhoff-Gustavson normal form is derived, with unitary transformations taking over the role of canonical transformations.
Abstract: A quantum analogue of the classical transformations to the Birkhoff-Gustavson normal form is derived. With unitary transformations taking over the role of canonical transformations, the author finds a striking similarity to Lie transformations in the classical case. The author suggests that the quantum normal form is identical to the Rayleigh-Schrodinger perturbation series and thus usually only asymptotic to the eigenvalues. The convergence question of both classical and quantum normal forms is discussed in some detail.
TL;DR: In this paper, four kinds of numerical models have been developed to investigate the quantum mechanical effect on charge control in HEMT's at room temperature, and a classical approach using Fermi statistics is shown to be able to predict the device performance with good accuracy, while the triangular-well approximation sometimes introduces serious errors.
Abstract: Four kinds of numerical models have been developed to investigate the quantum mechanical effect on charge control in HEMT's at room temperature. In spite of the two-dimensional nature of the channel electrons, a classical approach using Fermi statistics is shown to be able to predict the device performance with good accuracy, while the triangular-well approximation sometimes introduces serious errors.
TL;DR: In this article, a review of the physics of weak localization is discussed, which represents an interference experiment with conduction electrons split into pairs of waves interfering in the back-scattering direction.
Abstract: The resistance of two-dimensional electron systems such as thin disordered films shows deviations from Boltzmann theory, which are caused by quantum corrections and are called "weak localization" Theoretically, weak localization is originated by the Langer-Neal graph in the Kubo formalism In this review the physics of weak localization is discussed It represents an interference experiment with conduction electrons split into pairs of waves interfering in the back-scattering direction The intensity of the interference (integrated over the time) can be easily measured by the resistance of the film A magnetic field introduces a magnetic phase shift in the electronic wave function and suppresses the interference after a "flight" time proportional to 1/H Therefore the application of a magnetic field allows a time-of-flight experiment with conduction electrons Spin-orbit scattering rotates the spin of the electrons and yields an observable destructive interference Magnetic impurities destoy the coherence of the phase The experimental results as well as the theory is reviewed The role of the spin-orbit scattering and the magnetic scattering are discussed The measurements give selected information about the inelastic lifetime of the conduction electrons in disordered metals and raise new questions in solid state physics Future applications of the method of weak localization are considered and expected
TL;DR: In this paper, an integrable quantum chain model is constructed, describing the isotropic interaction of generalized "spins" transforming in the symmetric representations of SU(N), which is diagonalized exactly by the quantum inverse method.