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Showing papers in "Physical Review Letters in 1992"


Journal ArticleDOI
TL;DR: A generalization of the numerical renormalization-group procedure used first by Wilson for the Kondo problem is presented and it is shown that this formulation is optimal in a certain sense.
Abstract: A generalization of the numerical renormalization-group procedure used first by Wilson for the Kondo problem is presented. It is shown that this formulation is optimal in a certain sense. As a demonstration of the effectiveness of this approach, results from numerical real-space renormalization-group calculations for Heisenberg chains are presented.

5,625 citations


Journal ArticleDOI
TL;DR: In this article, the Hall conductance of a two-dimensional electron gas has been studied in a uniform magnetic field and a periodic substrate potential, where the Kubo formula is written in a form that makes apparent the quantization when the Fermi energy lies in a gap.
Abstract: The Hall conductance of a two-dimensional electron gas has been studied in a uniform magnetic field and a periodic substrate potential $U$. The Kubo formula is written in a form that makes apparent the quantization when the Fermi energy lies in a gap. Explicit expressions have been obtained for the Hall conductance for both large and small $\frac{U}{\ensuremath{\hbar}{\ensuremath{\omega}}_{c}}$.

4,811 citations


Journal ArticleDOI
TL;DR: The set of states accessible from an initial EPR state by one-particle operations are characterized and it is shown that in a sense they allow two bits to be encoded reliably in one spin-1/2 particle.
Abstract: As is well known, operations on one particle of an Einstein-Podolsky-Rosen (EPR) pair cannot influence the marginal statistics of measurements on the other particle. We characterize the set of states accessible from an initial EPR state by one-particle operations and show that in a sense they allow two bits to be encoded reliably in one spin-1/2 particle: One party, ``Alice,'' prepares an EPR pair and sends one of the particles to another party, ``Bob,'' who applies one of four unitary operators to the particle, and then returns it to Alice. By measuring the two particles jointly, Alice can now reliably learn which operator Bob used.

4,780 citations


Journal ArticleDOI
TL;DR: The standard Einstein-Maxwell equations in 2+1 spacetime dimensions, with a negative cosmological constant, admit a black hole solution that appears as a negative energy state separated by a mass gap from the continuous black hole spectrum.
Abstract: The standard Einstein-Maxwell equations in 2+1 spacetime dimensions, with a negative cosmological constant, admit a black hole solution. The 2+1 black hole---characterized by mass, angular momentum, and charge, defined by flux integrals at infinity---is quite similar to its 3+1 counterpart. Anti--de Sitter space appears as a negative energy state separated by a mass gap from the continuous black hole spectrum. Evaluation of the partition function yields that the entropy is equal to twice the perimeter length of the horizon.

3,640 citations


Journal ArticleDOI
TL;DR: It is predicted that carbon microtubules exhibit striking variations in electronic transport, from metallic to semiconducting with narrow and moderate band gaps, depending on the diameter of the tubule and on the degree of helical arrangement of the carbon hexagons.
Abstract: On the basis of realistic tight-binding band-structure calculations, we predict that carbon microtubules exhibit striking variations in electronic transport, from metallic to semiconducting with narrow and moderate band gaps, depending on the diameter of the tubule and on the degree of helical arrangement of the carbon hexagons. The origin of this drastic variation in the band structure is explained in terms of the two-dimensional band structure of graphite.

2,954 citations


Journal ArticleDOI
Charles H. Bennett1
TL;DR: It is shown that in principle any two nonorthogonal quantum states suffice, and a practical interferometric realization using low-intensity coherent light pulses is described.
Abstract: Quantum techniques for key distribution---the classically impossible task of distributing secret information over an insecure channel whose transmissions are subject to inspection by an eavesdropper, between parties who share no secret initially---have been proposed using (a) four nonorthogonally polarized single-photon states or low-intensity light pulses, and (b) polarization-entangled or spacetime-entangled two-photon states. Here we show that in principle any two nonorthogonal quantum states suffice, and describe a practical interferometric realization using low-intensity coherent light pulses.

2,786 citations


Journal ArticleDOI
TL;DR: A Landauer formula for the current through a region of interacting electrons is derived using the nonequilibrium Keldysh formalism, and an enhanced conductance is predicted for tunneling through a quantum dot in the fractional quantum Hall regime.
Abstract: A Landauer formula for the current through a region of interacting electrons is derived using the nonequilibrium Keldysh formalism. The case of proportionate coupling to the left and right leads, where the formula takes an especially simple form, is studied in more detail. Two particular examples where interactions give rise to novel effects in the current are discussed: In the Kondo regime, an enhanced conductance is predicted, while a suppressed conductance is predicted for tunneling through a quantum dot in the fractional quantum Hall regime.

2,392 citations


Journal ArticleDOI
TL;DR: A related but simpler EPR scheme is described and it is proved it secure against more general attacks, including substitution of a fake EPR source and the original 1984 key distribution scheme of Bennett and Brassard, which uses single particles instead of EPR pairs.
Abstract: Ekert has described a cryptographic scheme in which Einstein-Podolsky-Rosen (EPR) pairs of particles are used to generate identical random numbers in remote places, while Bell's theorem certifies that the particles have not been measured in transit by an eavesdropper. We describe a related but simpler EPR scheme and, without invoking Bell's theorem, prove it secure against more general attacks, including substitution of a fake EPR source. Finally we show our scheme is equivalent to the original 1984 key distribution scheme of Bennett and Brassard, which uses single particles instead of EPR pairs.

2,050 citations


Journal ArticleDOI
TL;DR: A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD) and applications are discussed to transition-metal and rare-earth magnetic systems.
Abstract: A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD). The integral of the CMXD signal over a given edge allows one to determine the ground-state expectation value of the orbital angular momentum. Applications are discussed to transition-metal and rare-earth magnetic systems.

2,041 citations


Journal ArticleDOI
TL;DR: The spectral response of a monolithic semiconductor quantum microcavity with quantum wells as the active medium displays mode splitting when the quantum wells and the optical cavity are in resonance.
Abstract: The spectral response of a monolithic semiconductor quantum microcavity with quantum wells as the active medium displays mode splitting when the quantum wells and the optical cavity are in resonance. This effect can be seen as the Rabi vacuum-field splitting of the quantum-well excitons, or more classically as the normal-mode splitting of coupled oscillators, the excitons, and the electromagnetic field of the microcavity. An exciton oscillator strength of 4\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ is deduced for 76-\AA{} quantum wells.

2,006 citations


Journal ArticleDOI
TL;DR: It is estimated that the mean-field transition temperature from a Peierls-distorted regime to a high-temperature metallic regime should be well below room temperature.
Abstract: We have calculated the electronic structure of a fullerene tubule using a first-principles, self-consistent, all-electron Gaussian-orbital based local-density-functional approach. Extending these results to a model containing an electron-lattice interaction, we estimate that the mean-field transition temperature from a Peierls-distorted regime to a high-temperature metallic regime should be well below room temperature. Such fullerene tubules should have the advantages (compared to the other conjugated carbon systems) of a carrier density similar to that of metals and zero band gap at room temperature.

Journal ArticleDOI
TL;DR: In this article, the interaction of ultra-intensemble laser pulses with a plasma was investigated and substantial absorption into heated electrons with a characteristic temperature of order the pondermotive potential was found.
Abstract: We use simulations to investigate the interaction of ultra-intense laser pulses with a plasma. With an intensity greater than ${10}^{18}$ W/${\mathrm{cm}}^{2}$, these pulses have a pressure greater than ${10}^{3}$ M bar and drive the plasma relativistically. Hole boring by the light beam is a key feature of the interaction. We find substantial absorption into heated electrons with a characteristic temperature of order the pondermotive potential. Other effects include a dependence on the polarization of the incident light, strong magnetic field generation, and a period of intense instability generation in the underdense plasma.

Journal ArticleDOI
TL;DR: Giant magnetoresistance in heterogeneous thin film Cu-Co alloys consisting of ultrafine Co-rich precipitate particles in a Cu-rich matrix is observed, modeled by including spin-dependent scattering at the interfaces between the particles and the matrix, as well as the spin- dependent scattering in the Co- rich particles.
Abstract: We have observed giant magnetoresistance in heterogeneous thin film Cu-Co alloys consisting of ultrafine Co-rich precipitate particles in a Cu-rich matrix. The magnetoresistance scales inversely with the average particle diameter. This behavior is modeled by including spin-dependent scattering at the interfaces between the particles and the matrix, as well as the spin-dependent scattering in the Co-rich particles.

Journal ArticleDOI
TL;DR: An alternative approach using a wave-function treatment to describe the atomic system and it is shown that this treatment is equivalent to the standard density matrix approach leading to the OBE's.
Abstract: A novel treatment of dissipation of energy from a ``small'' quantum system to a reservoir is presented. We replace the usual master equation for the small-system density matrix by a wave-function evolution including a stochastic element. This wave-function approach provides new insight and it allows calculations on problems which would otherwise be exceedingly complicated. The approach is applied here to a two- or three-level atom coupled to a laser field and to the vacuum modes of the quantized electromagnetic field.

Journal ArticleDOI
TL;DR: The observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids is shown to occur in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale.
Abstract: We have observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids. We show that GMR occurs in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale. The GMR is determined by the orientations of the magnetization axes, the density, and the size of the ferromagnetic entities.

Journal ArticleDOI
TL;DR: This work simulates an apparatus that learns to excite specified rotational states in a diatomic molecule and uses a learning procedure to direct the production of pulses based on fitness'' information provided by a laboratory measurement device.
Abstract: We simulate a method to teach a laser pulse sequences to excite specified molecular states. We use a learning procedure to direct the production of pulses based on ``fitness'' information provided by a laboratory measurement device. Over a series of pulses the algorithm learns an optimal sequence. The experimental apparatus, which consists of a laser, a sample of molecules and a measurement device, acts as an analog computer that solves Schr\"odinger's equation n/Iexactly, in real time. We simulate an apparatus that learns to excite specified rotational states in a diatomic molecule.

Journal ArticleDOI
TL;DR: A numerical simulation of the first-order phase transition in the 2D 10-state Potts model on lattices up to sizes 100 and a high-precision computation of the interfacial free energy per unit area is reported.
Abstract: Relying on the recent proposed multicanonical algorithm, we present a numerical simulation of the first-order phase transition in the 2D 10-state Potts model on lattices up to sizes 100\ifmmode\times\else\texttimes\fi{}100. It is demonstrated that the new algorithm lacks an exponentially fast increase of the tunneling time between metastable states as a function of the linear size L of the system. Instead, the tunneling time diverges approximately proportional to ${\mathit{L}}^{2.65}$. On our largest lattice we gain more than 2 orders of magnitude as compared to a standard heat-bath algorithm. As a first physical application we report a high-precision computation of the interfacial free energy per unit area.

Journal ArticleDOI
TL;DR: This work simulates the sorting of a mixture of two types of biological cells using a modified version of the large-Q Potts model with differential adhesivity and finds long-distance cell movement leading to sorting with a logarithmic increase in the length scale of homogeneous clusters.
Abstract: We simulate the sorting of a mixture of two types of biological cells using a modified version of the large-Q Potts model with differential adhesivity. We find long-distance cell movement leading to sorting with a logarithmic increase in the length scale of homogeneous clusters. Sorted clusters then round. We find two successive phases: A rapid boundary-driven creation of a low-cohesivity cell monolayer around the aggregate, and a slower boundary-independent internal rearrangement.

Journal ArticleDOI
TL;DR: It is found that ions can produce harmonics comparable in strength to those obtained from neutrals, and that the emission extends to much higher order.
Abstract: We present calculated optical harmonic spectra for atoms and ions in the high intensity regime to current short-pulse experiments. We find that ions can produce harmonics comparable in strength to those obtained from neutrals, and that the emission extends to much higher order. Simple scaling laws for the strength of the harmonic emission and the maximum observable harmonic are suggested. These results imply that the photoemission observed in recent experiments in helium and neon contains contributions from ions as well as neutrals.

Journal ArticleDOI
TL;DR: The influence of the film thickness on this process is investigated and compared to recent theoretical predictions of spinodal decomposition of partially wetting thin films.
Abstract: Thin polystyrene films (100 nm) on silicon substrates undergo dewetting when annealed above the glass transition temperature. Three different stages can be distinguished: The smooth films break up by the creation of cylindrical holes. The holes then grow and form rims ahead of them which finally contact each other creating ``cellular'' structures. The rims are unstable and decay into droplets. The influence of the film thickness on this process is investigated and compared to recent theoretical predictions of spinodal decomposition of partially wetting thin films.

Journal ArticleDOI
TL;DR: High-order scattering is found to be essential for the convergence of the multiple-scattering (MS) theory of x-ray-absorption fine structure, both in the near-edge and the extended regimes.
Abstract: High-order scattering is found to be essential for the convergence of the multiple-scattering (MS) theory of x-ray-absorption fine structure, both in the near-edge and the extended regimes. These contributions are calculated using an ab initio curved-wave scattering-matrix formalism. Convergence to full MS accuracy is demonstrated for fcc Cu, as well as for molecular ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$, where our approach provides a high-order MS interpretation of the ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ shape resonances.

Journal ArticleDOI
TL;DR: Results show that a small Josephson coupling between CuO double layers in a single crystal behaves like a series array of Josephson junctions which can exhibit mutual phase locking.
Abstract: We have observed Josephson coupling between CuO double layers in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ single crystals by direct measurements of ac and dc Josephson effects with current flow along the c axis. The results show that a small ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ single crystal behaves like a series array of Josephson junctions which can exhibit mutual phase locking.

Journal ArticleDOI
Hideo Ohno1, Hideo Ohno2, H. Munekata2, T. Penney2, S. von Molnar2, L. L. Chang2 
TL;DR: The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.
Abstract: Magnetotransport properties of p-type (In,Mn)As, a new diluted magnetic semiconductor based on a III-V semiconductor, are studied. The interaction between the holes and the Mn 3d spins is manifested in the anomalous Hall effect, which dominates the Hall resistivity from low temperature (0.4 K) to nearly room temperature, and in the formation of partial ferromagnetic order below 7.5 K, which is a cooperative phenomenon related to carrier localization. The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.

Journal ArticleDOI
TL;DR: The Einstein-Podolsky-Rosen paradox is demonstrated experimentally for dynamical variables having a continuous spectrum, where the continuous optical amplitudes of a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam generated by nondegenerate parametric amplification.
Abstract: The Einstein-Podolsky-Rosen paradox is demonstrated experimentally for dynamical variables having a continuous spectrum. As opposed to previous work with discrete spin or polarization variables, the continuous optical amplitudes of a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam generated by nondegenerate parametric amplification. The uncertainty product for the variances of these inferences is observed to be 0.70±0.01, which is below the limit of unity required for the demonstration of the paradox.

Journal ArticleDOI
TL;DR: An investigation of the spectral response of a small collection of two-state atoms strongly coupled to the field of a high-finesse optical resonator finds a coupling-induced normal-mode splitting even for one intracavity atom, representing a direct spectroscopic measurement of the so-called vacuum Rabi splitting for the atom-cavity system.
Abstract: An investigation of the spectral response of a small collection of two-state atoms strongly coupled to the field of a high-finesse optical resonator is described for mean number N¯≤10 atoms. For weak excitation, a coupling-induced normal-mode splitting is observed even for one intracavity atom, representing a direct spectroscopic measurement of the so-called vacuum Rabi splitting for the atom-cavity system.

Journal ArticleDOI
TL;DR: The diffuseness of the ferroelectric phase transition in PbMg-Nb 2/3 is proposed to be due to quenched random electric fields originating from charged compositional fluctuations.
Abstract: The diffuseness of the ferroelectric phase transition in ${\mathrm{PbMg}}_{1/3}$${\mathrm{Nb}}_{2/3}$${\mathrm{O}}_{3}$ is proposed to be due to quenched random electric fields originating from charged compositional fluctuations. They are responsible for the extreme critical slowing down, the freezing into nanometric ferroelectric domains, and the slow relaxation of the polarization below ${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}212 K. Barkhausen jumps during poling exclude glassiness, which was conjectured previously. At ${\mathit{T}}_{\mathit{c}}$ a ferroelectric anomaly of the dielectric permittivity appears, if the random fields are overcome by an external electric field.

Journal ArticleDOI
TL;DR: A new nonconservative self-organized critical model is introduced that is equivalent to a quasistatic two-dimensional version of the Burridge-Knopoff spring-block model of earthquakes and displays a robust power-law behavior.
Abstract: We introduce a new nonconservative self-organized critical model. This model is equivalent to a quasistatic two-dimensional version of the Burridge-Knopoff spring-block model of earthquakes. Our model displays a robust power-law behavior. The exponent is not universal; rather it depends on the level of conservation. A dynamical phase transition from localized to nonlocalized behavior is seen as the level of conservation is increased. The model gives a good prediction of the Gutenberg-Richter law and an explanation to the variances in the observed b values.

Journal ArticleDOI
Richard F. Voss1
TL;DR: Spectral density measurements of individual base positions demonstrate the ubiquity of low-frequency 1/f β noise and long-range fractal correlations as well as prominent short-range periodicities.
Abstract: A new method of quantifying correlations in symbolic sequences is applied to DNA nucleotides. Spectral density measurements of individual base positions demonstrate the ubiquity of low-frequency 1/${\mathit{f}}^{\mathrm{\ensuremath{\beta}}}$ noise and long-range fractal correlations as well as prominent short-range periodicities. Ensemble averages over classifications in the GenBank databank (primate, invertebrate, plant, etc.) show systematic changes in spectral exponent \ensuremath{\beta} with evolutionary category.

Journal ArticleDOI
TL;DR: A molecular-dynamics calculation on a hydrated protein, crambin, demonstrates that neighboring dihedral angles are correlated to local transitions in the protein backbone, and that the amplitude of collective excitations, representing correlated global motions in theprotein, samples multicentered distributions.
Abstract: A molecular-dynamics calculation on a hydrated protein, crambin, demonstrates that (i) neighboring dihedral angles are correlated to local transitions in the protein backbone, and that (ii) the amplitude of collective excitations, representing correlated global motions in the protein, samples multicentered distributions. The time dependence of the multicentered dihedral and collective excitations show rapid transitions from the center of one distribution to another, followed for some time by damped, low-amplitude motions around one center. The global nonlinear collective excitations are responsible for most of the atomic fluctuations of the molecule. An analysis appropriate to multimodal conformations is reported.

Journal ArticleDOI
TL;DR: It is shown that for repulsive electron interactions, the electrons are completely reflected by even the smallest scatterer, leading to a truly insulating weak link, in striking contrast to that for noninteracting electrons.
Abstract: We study theoretically the transport of a one-channel Luttinger liquid through a weak link. For repulsive electron interactions, the electrons are completely reflected by even the smallest scatterer, leading to a truly insulating weak link, in striking contrast to that for noninteracting electrons. At finite temperature (T) the conductance is nonzero, and is predicted to vanish as a power of T. At T=0 power-law current-voltage characteristics are predicted. For attractive interactions, a Luttinger liquid is argued to be perfectly transmitted through even the largest of barriers. The role of Fermi-liquid leads is also explored.