Uncorrelated System Research Articles

Generation of Macroscopic Superpositions of Quantum States by Linear Coupling to a Bath

We demonstrate through an exactly solvable model that collective coupling to any thermal bath induces effectively nonlinear couplings in a quantum many-body (multispin) system. The resulting evolution can drive an uncorrelated large-spin system with high probability into a macroscopic quantum-superposition state. We discuss possible experimental realizations.

Robust optimization for the correlated MIMO downlink with imperfect channel state information

To reduce the performance deterioration induced by imperfect channel state information (CSI) in correlated multiple input multiple output(MIMO) downlink, the linear transmit/receive filters should be optimized to be robust to imperfect CSI. A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed. The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI. Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance. In addition, the effect of spatial correlation on the performance of the proposed algorithm is also simulated.

Characteristic of alternating current hopping conductivity in one-dimensional binary disordered system with off-diagonal correlations

Based on a tight-binding disordered model describing a single electron band, we establish a model of one-dimensional binary disordered systems with off-diagonal correlations, and derive the alternating current (ac) conductance formula. By calculating the ac conductivity, the function of disorder and off-diagonal correlations in electronic transport are analyzed, and the dependence of the ac conductivity on the field frequency and the temperature is studied. The results indicate that the ac conductivity of one-dimensional binary disordered system decreases with the increasing of the degree of lattices energy disorder. And the ac conductivity of the system is also dependent on the probabilities p, which represents the degree of compositional disorder of the system to some extent. The ac conductivity of system first decreases with the increasing of p, then increases with farther increasing of p. We also find that off-diagonal correlations lead to delocalization and enhance the ac conductivity of the system，namely, the ac conductivity of one-dimensional binary disordered system with off-diagonal correlations is larger than that of uncorrelated system in the Anderson limit. Moreover, the ac conductivity of one-dimensional binary disordered system decreases with the increasing of temperature, and increases drastically with the increasing of the frequency of the electric field.

Predicting DNAPL entrapment and recovery: the influence of hydraulic property correlation

The influence of aquifer property correlation on multiphase fluid migration, entrapment and recovery was explored by incorporating correlated and uncorrelated porosity, permeability, and capillary pressure-saturation (Pc-Sat) parameter fields in a cross-sectional numerical multiphase flow model. Comparison of two-dimensional entrapped organic saturation distributions for a simulated tetrachloroethylene (PCE) spill in ensembles of aquifer realizations suggests that the degree of spatial correlation in Pc-Sat parameters exerts a controlling influence on dense nonaqueous phase liquid (DNAPL) spreading and redistribution in saturated aquifers. The predicted evolution of DNAPL source zones and resultant remediation efficiency under surfactant enhanced aquifer remediation (SEAR) also appear to be strongly influenced by the spatial correlation of aquifer parameters and multiphase flow constitutive relationships. Results for a limited number of realizations selected from each ensemble showed that removal of 60% to 99% of entrapped PCE could reduce dissolved contaminant concentration and mass flux by approximately two orders of magnitude under natural gradient conditions. Aqueous phase contaminant mass flux did not vary uniformly as a function of % DNAPL removed, however, and notable differences in behavior were observed for models incorporating correlated versus uncorrelated Pc-Sat and permeability fields. Although these results must be confirmed through analysis of additional realizations, it is likely that similar or larger differences between correlated and uncorrelated system behavior will be observed in aquifers with greater spatially variability than that of the nonuniform, homogeneous sand aquifer studied here.

Noninteracting Electrons and the Metal-Insulator Transition in Two Dimensions with Correlated Impurities

While standard scaling arguments show that a system of noninteracting electrons in two dimensions and in the presence of uncorrelated disorder is insulating, in this paper we discuss the case where interimpurity correlations are included. We find that for pointlike impurities and an infinite interimpurity correlation length, a mobility edge exists in 2D even if the individual impurity potentials are random. In the uncorrelated system we recover the scaling results, while in the intermediate regime for length scales comparable to the correlation length, the system behaves like a metal but with increasing fluctuations, before strong localization eventually takes over for length scales much larger than the correlation length. In the intermediate regime, the relevant length scale is given by the interimpurity correlation length, with important consequences for high mobility systems.

One Dimensional Face-to-Face Stacking of Anderson–Evans [Cr(OH)6Mo6O18]3-Polyoxometalate Anion: Synthesis, Structure, and Physical Properties of (BEDT-TTF)4[Cr(OH)6Mo6O18] 2H2O

The synthesis, structural and magnetic characterizations of a new charge transfer salt (BEDT-TTF)4[Cr(OH)6Mo6O18]⋅2H2O based on the planar paramagnetic Anderson–Evans polyoxometalate are reported. Structural parameters: T=293 K, triclinic (P $$\bar 1$$ ), a=5.9545(2) A, b=16.3767(6) A, c=21.8643(6) A, α=110.829(2)°, β=91.262(2)°, γ=98.129(1)°, Z=1, R=0.0540. The crystal structure is characterized by a face-to-face stacking of the anions giving rise to a one-dimensional inorganic chain which develops along the a direction. The organic layers contain two crystallographically independent BEDT-TTF dimers that form alternating stacks along the b direction. This organic chain is perpendicular to the inorganic chains. The charges on BEDT-TTF dimers are deduced to +1.2(1) and +1.7(1) on the basis of the intramolecular bond lengths. The EPR spectrum at 2.5 K is characterized by the superposition of BEDT-TTF•+ and [CrIII(OH)6Mo6O18]3− signals. The static susceptibility can be fitted by the Curie–Weiss law down to 1.9 K and the magnetic moment at 300 K is estimated to 4.21μ B , suggesting the uncorrelated spin system with BEDT-TTF•+ (S=1/2) and CrIII (S=3/2) ions. This interpretion is consistent with the charge disproportionation on BEDT-TTF dimers along the stack, which is supported by the refined molecular structure and is closely related to the insulating behavior (<10−9S⋅cm−1 at RT).

Measured performance of an endfire superdirective line array in littoral water

Superdirective line arrays can provide high gains whenever the interelement spacing is much less than half a wavelength. In practice these arrays have fallen short for two reasons: First, performance degrades appreciably in the presence of uncorrelated system noise. Second, the optimum array weights are specific to the form of the noise field and the choice of these weights is often sensitive to deviations from that noise field. Furthermore, since the process involves computing signal differences between hydrophones, the signal to noise ratio (SNR) degrades as the steering angle approaches broadside. In spite of these drawbacks, a superdirective array can provide substantial improvement over a conventional array in specific instances. For example, the present application requires an endfire array of limited extent (1 m in length) and wide bandwidth (1–5 kHz) making a conventional array impractical. Moreover, improvements in array hardware have substantially reduced uncorrelated system noise, and increased computer speed makes it reasonable to process data using several weighting schemes. In this paper, the superdirective array will be described and its measured performance will be compared to theoretical predictions.

High resolution imaging with multilayer telescopes: resolution performance of the MSSTA II telescopes

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory composed of a set of normal-incidence multilayer-coated telescopes that obtained selected bandpass spectroheliograms (44 to 1550 Aa) of the solar atmosphere. These spectroheliograms were recorded on specially fabricated XUV and FUV 70-mm Kodak film. Rocket launches of this instrument payload took place in 1991 (MSSTA I) and 1994 (MSSTA II) at the White Sands Missile Test Range in New Mexico, sponsored by the National Aeronautics and Space Administration (NASA) sounding rocket experiment program. Immediately prior to the 1994 launch, visible light focusing tests of each telescope were performed in situ using a 1951 standard Air Force high-resolution test target, to measure optical resolution performance. We determined that the MSSTA II telescopes performed at diffraction-limited resolutions down to 0.70 arcsec at visible wavelengths. Based on these measurements, we calculate an upper bound to the focusing errors that incorporate the sum of all uncorrelated system focus errors that affect resolution performance. Coupling these upper bound estimates with the in-band diffraction limits, surface scattering errors and payload pointing jitter, we demonstrate that 11 of 19 MSSTA II telescopes--having negligible figures of focus errors in comparison to the corresponding visible diffraction limits--performed atmore » sub arcsecond resolution at their operational FUV/EUV/XUV wavelengths during flight. We estimate the in-band performance down to 0.14{+-}0.08 arcsec. (c) 2000 Society of Photo-Optical Instrumentation Engineers.« less

Effect of partial ordering of a two-dimensional system of scatterers on the anisotropy of its kinetic coefficients

The effect of partial ordering of impurities (correlated along one direction and uncorrelated along the other) on the kinetic coefficients is considered. It is shown that the geometry of the spatial impurity distribution by itself has no effect on the diffusion coefficient or conductivity for scattering by a spherically symmetric potential, and these coefficients remain the same as for an uncorrelated system of impurities.

Interchain coupling and electron-electron interaction in conjugated polymers

The influence of the Hubbard interaction on the lattice structure of two half-filled Su-Shrieffer-Heeger chains coupled by constant electron hoppings is examined using a linked cluster expansion of the Gutzwiller variational wave function as well as second-order perturbation theory. Parallel and antiparallel dimerized crystal structures are considered. In the uncorrelated system the metallic undimerized and the insulating parallel dimerized phase compete. However, the state of lowest energy is antiparallel dimerized. In the case of finite Hubbard interaction both the variational and the perturbational approach yield a stabilization of the parallel dimerized configuration. For the parallel dimerized model, the Gutzwiller ansatz signals a new ordering of the electrons in the bands: holes are present in the highest occupied single-particle states; the upper valence band is occupied and the lower conduction band is empty even in the 'metallic' phase characterized by crossing bands.

Theory of hydrogen hopping dynamics including hydrogen-lattice correlations

A theory is formulated to incorporate effects of correlations in the hydrogen-lattice vibrations into the description of the intersite hopping dynamics of hydrogen (and similar light interstitials) in metals. A suitable model is proposed, the theoretical treatment is sketched and the resulting hopping rate expression is presented. It is discussed that in “normal” cases the obtained hopping rate formula can be cast into the form for an uncorrelated system but with suitably renormalized parameters. The theory is shown to reproduce well the hopping rate (diffusion coefficient) for hydrogen and deuterium in tantalum and copper and for μ+ in copper.

Self-noise in interferometers

AbstractWe study the distribution of noise in images synthesized by radio interferometers, focusing particularly on the noise due to source power fluctuations. For a total power interferometer, the r.m.s. fluctuation in the image consists of a term that is constant all over the map, which is the uncorrelated system noise divided by the number of telescopes in the interferometer, and a term that is the image itself. For a correlation interferometer the expression is not so simple but is qualitatively similar. Our results are consistent with intuitive expectations in various observing situations. We find similarities in self-noise at optical and radio wavelengths.

Mean square deviation from a slater determinant and scaling effects in models of the correlated ground state of nuclear matter and of 208Pb

It is proposed to characterize the deviation of the one-body density matrix, ϱ, of the correlated nuclear ground state from that, ϱ 0 , of an uncorrelated system by the following quantity σ = A −1 tr ( ϱ− ϱ 0) 2, where A is the number of nucleons. This “mean square deviation per nucleon” σ has a lower bound, σ min, which is reached when the uncorrelated many-body wave function is constructed with the natural orbitals. It is shown that in the case of nuclear matter this minimum can be expressed in terms of the momentum probability distribution. In a nucleus the expression of σ min involves the occupation probabilities of the natural orbitals; it is argued that σ min ≈ 0.02–0.03 for realistic nucleon-nucleon interactions. The value of σ min is evaluated in the case of various models which have recently been introduced in order to study the effect of correlations on the density and momentum distributions of protons in 208Pb. We investigate how the latter quantities are modified when previous approximations for the natural orbitals are modified by performing either a scaling transformation or by changing the Woods-Saxon potential from which these natural orbitals are generated. Two sets of single-particle orbitals are found which yield good agreement with the experimental values of both the charge and momentum density distributions of 208Pb when realistic occupation probabilities are introduced; the latter correspond to a 11.6% depletion of the Fermi sea, of which only 3.6% arise from long-range correlations as described by the random phase approximation.

Temporal correlation measurements of pulsed dual CO_2 lidar returns

The temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets have been measured by using a pulsed dual-laser direct-detection lidar system operating near 10.6 microm. Our results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times of the order of 1-3 msec or less. However, only incomplete correlation was achieved; the diffuse target returns yielded much lower correlation than that obtained with the specular targets. This is shown to be due to uncorrelated system noise effects and different statistics for the two types of target returns.

Theory of the optical potential for strongly interacting particles

We use the insight gained from the study of analyticity and unitarity to suggest a new method for the construction of the optical potential for strongly interacting particles. The calculational procedures suggested in this work are such as to associate a distinct physical process with each term in our expansion of the optical potential. By starting with various decompositions of the A-body target wave function we can obtain theories of varying complexity. Introducing a decomposition with respect to states of the (A-1) -body system, we obtain a construction of the optical potential based upon the single-scattering approximation. If we introduce a decomposition of the target ground state with respect to states of the (A-2) -body system we obtain a more complex theory. In the extended theory, the first-order optical potential of the simpler model is readily extracted along with a second-order potential that depends on the detailed structure of the two-body density matrix of the target. The role of Pauli and short-range correlations in modifying the calculation of the second-order potential is discussed. The physical picture that emerges from this analysis is different from that obtained from multiple-scattering theory, although the two theories are in general agreement as to themore » nature of the first-order optical potential. When the fixed-scatterer approximation is used to simplify calculations based upon multiple-scattering theory, the second-order optical potential is found to depend on the two-body correlation function. In contrast, for the theory presented here, we find that the inclusion of Pauli and/or short-range correlations is a relatively minor aspect in the construction of the second-order potential. Indeed, we would obtain a second-order potential for an uncorrelated system.« less

Cluster-variation method for the momentum distribution in narrow bands

The Kikuchi method (cluster-variation method) has been used to improve the Gutzwiller's result for the momentum distribution in narrow-band systems. The distribution so obtained is no longer a step function consisting of two constant values. The discontinuity of the distribution function at the Fermi surface of the uncorrelated system is substantially increased in the regime of strong correlation.

Box, Jenkins-Åström and Kalman linear control laws and their equivalence

A state-space equivalent of the general Box, Jenkins—Åström single input/output, discrete stochastic-system model is given. The ‘noise’ estimates from them are shown to be the same. It is suggested that equivalence of the controls, for the same cost function, follows directly; but the equivalence is also demonstrated more formally. The relation of these results to those for a model with uncorrelated system and measurement noise, and to ‘multistage’ control, is also dealt with.

Variational solutions of perturbation theory equations

A procedure is demonstrated to obtain the solution of the partial differential equations of perturbation theory by choosing the functionals to be made stationary directly from the equations themselves. This procedure is shown to be simpler in many-particle problems than the usual Ritz-Schrödinger or Hylleraas-Bethe-Salpeter procedures which choose the functionals so that their extremum values are identically equal to certain energy eigenvalues. As examples variational principles for the second-order Hartree-Fock energy and the second-order energy of an uncorrelated system in an electric field are derived.

Onset of Correlation in Initially Uncorrelated System

The system under consideration is a number of molecules contained in a resonant cavity and isolated from external influences. The molecules are assumed to have two energy levels, and the molecular frequencies have a Gaussian distribution centered at the cavity frequency; the initial states of the molecules are uncorrelated. The onset of correlation in the molecular behavior is studied by examining the field in the cavity and the power emitted by the molecules for effects depending on the square of the number of molecules, in a perturbation theory approach.It is shown that correlation effects manifest themselves in the fourth order interaction. Both the correlation energy in the field and the correlation power emitted by the molecules approach steady-state values after transient periods determined by the relaxation time of the cavity and the frequency spread of the molecules. A physical picture of the correlation effects, as being due to induced emission produced by the lowest order spontaneous and thermal emission, is investigated and found to be approximately correct. The ratio of correlation energy to lowest order spontaneous emission energy is derived. An analysis is made of the dependence of the results on the initial states of the molecules, and interpreted in terms of the physical picture. The effect of the presence of a number of cavity modes, rather than a single mode, within the frequency spread of the molecules is investigated under simplifying assumption, and is shown to multiply the correlation effects by the square of the number of modes.