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Showing papers in "Physical Review Letters in 1998"


Journal ArticleDOI
TL;DR: In this article, an explicit formula for the entanglement of formation of a pair of binary quantum objects (qubits) as a function of their density matrix was conjectured.
Abstract: The entanglement of a pure state of a pair of quantum systems is defined as the entropy of either member of the pair. The entanglement of formation of a mixed state $\ensuremath{\rho}$ is the minimum average entanglement of an ensemble of pure states that represents \ensuremath{\rho}. An earlier paper conjectured an explicit formula for the entanglement of formation of a pair of binary quantum objects (qubits) as a function of their density matrix, and proved the formula for special states. The present paper extends the proof to arbitrary states of this system and shows how to construct entanglement-minimizing decompositions.

6,999 citations


Journal ArticleDOI
TL;DR: The condition of self-adjointness as discussed by the authors ensures that the eigenvalues of a Hamiltonian are real and bounded below, replacing this condition by the weaker condition of $\mathrm{PT}$ symmetry, one obtains new infinite classes of complex Hamiltonians whose spectra are also real and positive.
Abstract: The condition of self-adjointness ensures that the eigenvalues of a Hamiltonian are real and bounded below. Replacing this condition by the weaker condition of $\mathrm{PT}$ symmetry, one obtains new infinite classes of complex Hamiltonians whose spectra are also real and positive. These $\mathrm{PT}$ symmetric theories may be viewed as analytic continuations of conventional theories from real to complex phase space. This paper describes the unusual classical and quantum properties of these theories.

5,626 citations


Journal ArticleDOI
Y. Fukuda1, T. Hayakawa1, E. Ichihara1, Kunio Inoue1, K. Ishihara1, H. Ishino1, Yoshitaka Itow1, Takaaki Kajita1, J. Kameda1, S. Kasuga1, Ken-ichiro Kobayashi1, Yohei Kobayashi1, Yusuke Koshio1, M. Miura1, Masayuki Nakahata1, S. Nakayama1, A. Okada1, Ko Okumura1, N. Sakurai1, Masato Shiozawa1, Yoshihiro Suzuki1, Y. Takeuchi1, Y. Totsuka1, Shinya Yamada1, M. Earl2, Alec Habig2, E. Kearns2, M. D. Messier2, Kate Scholberg2, J. L. Stone2, Lawrence Sulak2, C. W. Walter2, M. Goldhaber3, T. Barszczxak4, D. Casper4, W. Gajewski4, P. G. Halverson4, J. Hsu4, W. R. Kropp4, L. R. Price4, Frederick Reines4, Michael B. Smy4, Henry W. Sobel4, Mark R. Vagins4, K. S. Ganezer5, W. E. Keig5, R. W. Ellsworth6, S. Tasaka7, J. W. Flanagan8, A. Kibayashi8, John G. Learned8, S. Matsuno8, V. J. Stenger8, D. Takemori8, T. Ishii, Junichi Kanzaki, T. Kobayashi, S. Mine, K. Nakamura, K. Nishikawa, Yuichi Oyama, A. Sakai, Makoto Sakuda, Osamu Sasaki, S. Echigo9, M. Kohama9, A. T. Suzuki9, Todd Haines10, Todd Haines4, E. Blaufuss11, B. K. Kim11, R. Sanford11, R. Svoboda11, M. L. Chen12, Z. Conner12, Z. Conner13, J. A. Goodman12, G. W. Sullivan12, J. Hill14, C. K. Jung14, K. Martens14, C. Mauger14, C. McGrew14, E. Sharkey14, B. Viren14, C. Yanagisawa14, W. Doki15, Kazumasa Miyano15, H. Okazawa15, C. Saji15, M. Takahata15, Y. Nagashima16, M. Takita16, Takashi Yamaguchi16, Minoru Yoshida16, Soo-Bong Kim17, M. Etoh18, K. Fujita18, Akira Hasegawa18, Takehisa Hasegawa18, S. Hatakeyama18, T. Iwamoto18, M. Koga18, Tomoyuki Maruyama18, Hiroshi Ogawa18, J. Shirai18, A. Suzuki18, F. Tsushima18, Masatoshi Koshiba1, M. Nemoto19, Kyoshi Nishijima19, T. Futagami20, Y. Hayato20, Y. Kanaya20, K. Kaneyuki20, Y. Watanabe20, D. Kielczewska4, D. Kielczewska21, R. A. Doyle22, J. S. George22, A. L. Stachyra22, L. Wai22, L. Wai23, R. J. Wilkes22, K. K. Young22 
Abstract: We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ oscillations with ${sin}^{2}2\ensuremath{\theta}g0.82$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}l\ensuremath{\Delta}{m}^{2}l6\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}3}\mathrm{eV}{}^{2}$ at 90% confidence level.

3,784 citations


Journal ArticleDOI
TL;DR: In this article, the authors examine the possibility that a significant component of the energy density of the universe has an equation of state different from that of matter, radiation, or cosmological constant.
Abstract: We examine the possibility that a significant component of the energy density of the Universe has an equation of state different from that of matter, radiation, or cosmological constant ( $\ensuremath{\Lambda}$). An example is a cosmic scalar field evolving in a potential, but our treatment is more general. Including this component alters cosmic evolution in a way that fits current observations well. Unlike $\ensuremath{\Lambda}$, it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum.

3,400 citations


Journal ArticleDOI
TL;DR: In this paper, the Bose-Hubbard model was used to model the phase transition from the superfluid to the Mott insulator phase induced by varying the depth of the optical potential.
Abstract: The dynamics of an ultracold dilute gas of bosonic atoms in an optical lattice can be described by a Bose-Hubbard model where the system parameters are controlled by laser light We study the continuous (zero temperature) quantum phase transition from the superfluid to the Mott insulator phase induced by varying the depth of the optical potential, where the Mott insulator phase corresponds to a commensurate filling of the lattice (``optical crystal'') Examples for formation of Mott structures in optical lattices with a superimposed harmonic trap and in optical superlattices are presented

2,873 citations


Journal ArticleDOI
TL;DR: This work presents a scheme of a quantum repeater that connects a string of (imperfect) entangled pairs of particles by using a novel nested purification protocol, thereby creating a single distant pair of high fidelity.
Abstract: In quantum communication via noisy channels, the error probability scales exponentially with the length of the channel. We present a scheme of a quantum repeater that overcomes this limitation. The central idea is to connect a string of (imperfect) entangled pairs of particles by using a novel nested purification protocol, thereby creating a single distant pair of high fidelity. Our scheme tolerates general errors on the percent level, it works with a polynomial overhead in time and a logarithmic overhead in the number of particles that need to be controlled locally.

2,787 citations


Journal ArticleDOI
TL;DR: Perdew, Burke, and Ernzerhof as mentioned in this paper offer a reply to the authors of the letter, which they call a "comment on the letter". But they do not provide a comment on its content.
Abstract: A Comment on the Letter by John P. Perdew, Kieron Burke, and Matthias Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996). The authors of the Letter offer a Reply.

2,261 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that many coupled oscillator array configurations considered in the literature can be put into a simple form so that determining the stability of the synchronous state can be done by a master stability function, which can be tailored to one's choice of stability requirement.
Abstract: We show that many coupled oscillator array configurations considered in the literature can be put into a simple form so that determining the stability of the synchronous state can be done by a master stability function, which can be tailored to one's choice of stability requirement. This solves, once and for all, the problem of synchronous stability for any linear coupling of that oscillator.

2,209 citations


Journal ArticleDOI
TL;DR: In this paper, the expectation values of an operator similar to the Wilson loop in the large $N$ limit of field theories were calculated for supersymmetric Yang-Mills theory.
Abstract: We propose a method to calculate the expectation values of an operator similar to the Wilson loop in the large $N$ limit of field theories. We consider $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4$ $(3+1)$-dimensional supersymmetric Yang-Mills theory. The prescription involves calculating the area of a fundamental string world sheet in certain supergravity backgrounds. We also consider the case of coincident $M$-theory five-branes where one is led to calculating the area of $M$-theory two-branes. We briefly discuss the computation for $(2+1)$-dimensional supersymmetric Yang-Mills theory with 16 supercharges which is nonconformal. In all of these cases, we calculate the energy of a quark-antiquark pair.

2,117 citations


Journal ArticleDOI
TL;DR: In this article, self-consistent density functional calculations for the adsorption of O and CO, and the dissociation of CO on strained and unstrained Ru(0001) surfaces are used to show how strained metal surfaces have chemical properties that are significantly different from those of un-strained surfaces.
Abstract: Self-consistent density functional calculations for the adsorption of O and CO, and the dissociation of CO on strained and unstrained Ru(0001) surfaces are used to show how strained metal surfaces have chemical properties that are significantly different from those of unstrained surfaces. Surface reactivity increases with lattice expansion, following a concurrent up-shift of the metal $d$ states. Consequences for the catalytic activity of thin metal overlayers are discussed.

1,905 citations


Journal ArticleDOI
TL;DR: It is shown that decoherence-free subspaces are stable to perturbations and, moreover, that universal quantum computation is possible within them.
Abstract: Decoherence in quantum computers is formulated within the semigroup approach The error generators are identified with the generators of a Lie algebra This allows for a comprehensive description which includes as a special case the frequently assumed spin-boson model A generic condition is presented for errorless quantum computation: decoherence-free subspaces are spanned by those states which are annihilated by all the generators It is shown that these subspaces are stable to perturbations and, moreover, that universal quantum computation is possible within them

Journal ArticleDOI
TL;DR: In this article, a strong violation of Bell's inequality was observed in an Einstein-Podolsky-Rosen-type experiment with independent observers, where the necessary spacelike separation of the observations is achieved by sufficient physical distance between the measurement stations, by ultrafast and random setting of the analyzers, and by completely independent data registration.
Abstract: We observe strong violation of Bell's inequality in an Einstein-Podolsky-Rosen-type experiment with independent observers. Our experiment definitely implements the ideas behind the well-known work by Aspect et al. We for the first time fully enforce the condition of locality, a central assumption in the derivation of Bell's theorem. The necessary spacelike separation of the observations is achieved by sufficient physical distance between the measurement stations, by ultrafast and random setting of the analyzers, and by completely independent data registration.

Journal ArticleDOI
TL;DR: In this article, a one-dimensional scattering amplitude and effective 1D interaction potential for atoms confined transversally by an atom waveguide or highly elongated ''cigar''-shaped atomic trap was calculated.
Abstract: We calculate, within the pseudopotential approximation, a one-dimensional scattering amplitude and effective one-dimensional interaction potential for atoms confined transversally by an atom waveguide or highly elongated ``cigar''-shaped atomic trap. We show that, in the low-energy scattering regime, the scattering process degenerates to a total reflection, suggesting an experimental realization of a famous model in theoretical physics---a one-dimensional gas of impenetrable bosons (``Tonks'' gas). We give an estimate for suitable experimental parameters for alkali atoms confined in waveguides.

Journal ArticleDOI
TL;DR: In this paper, a phenomenological thermodynamic theory of ferroelectric thin films epitaxially grow on cubic substrates is developed using a new form of the thermodynamic potential, which corresponds to the ac tual mechanical boundary conditions of the problem.
Abstract: A phenomenological thermodynamic theory of ferroelectric thin films epitaxially grow on cubic substrates is developed using a new form of the thermodynamic potential. which corresponds to the ac tual mechanical boundary conditions of the problem, For single-domain BaTiO3 and PbTiO3 films, the "misfit-temperature" phase diagrams are constructed. It is found that the 2D clamping of the films, apart from a shift of the temperature of the ferroelectric transition, results in a change of its order. A change of the sequence of the phases and the appearance of phases forbidden in the bulk crystals are predicted. [S0031-9007(98)05421-0].

Journal ArticleDOI
TL;DR: It is revealed that the temporal evolution of the peripheral tremor rhythms directly reflects the time course of the synchronization of abnormal activity between cortical motor areas.
Abstract: We use the concept of phase synchronization for the analysis of noisy nonstationary bivariate data. Phase synchronization is understood in a statistical sense as an existence of preferred values of the phase difference, and two techniques are proposed for a reliable detection of synchronous epochs. These methods are applied to magnetoencephalograms and records of muscle activity of a Parkinsonian patient. We reveal that the temporal evolution of the peripheral tremor rhythms directly reflects the time course of the synchronization of abnormal activity between cortical motor areas.

Journal ArticleDOI
TL;DR: In this paper, a protocol for teleportation of a single mode of the electromagnetic field with high fidelity using squeezed-state entanglement and current experimental capability is presented, including the roles of finite quantum correlation and nonideal detection efficiency.
Abstract: Quantum teleportation is analyzed for states of dynamical variables with continuous spectra, in contrast to previous work with discrete (spin) variables. The entanglement fidelity of the scheme is computed, including the roles of finite quantum correlation and nonideal detection efficiency. A protocol is presented for teleporting the wave function of a single mode of the electromagnetic field with high fidelity using squeezed-state entanglement and current experimental capability.

Journal ArticleDOI
TL;DR: In this article, a quantum optical experimental implementation of teleportation of unknown pure quantum states was reported, which realizes all of the nonlocal aspects of the original scheme proposed by Bennett et al. and is equivalent to it up to a local operation.
Abstract: We report on a quantum optical experimental implementation of teleportation of unknown pure quantum states. This realizes all of the nonlocal aspects of the original scheme proposed by Bennett et al. and is equivalent to it up to a local operation. We exhibit results for the teleportation of a linearly polarized state and of an elliptically polarized state. We show that the experimental results cannot be explained in terms of a classical channel alone. The Bell measurement in our experiment can distinguish between all four Bell states simultaneously allowing, in the ideal case, a 100% success rate of teleportation. [S0031-9007(97)05275-7]

Journal ArticleDOI
TL;DR: In this article, a comparative study of the energetic, structural, and elastic properties of carbon and composite single-wall nanotubes is presented, using a nonorthogonal tight-binding formalism.
Abstract: We present a comparative study of the energetic, structural, and elastic properties of carbon and composite single-wall nanotubes, including BN, ${\mathrm{BC}}_{3}$, and ${\mathrm{BC}}_{2}\mathrm{N}$ nanotubes, using a nonorthogonal tight-binding formalism. Our calculations predict that carbon nanotubes have a higher Young modulus than any of the studied composite nanotubes, and of the same order as that found for defect-free graphene sheets. We obtain good agreement with the available experimental results.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the observation of discrete spatial optical solitons in an array of 41 waveguides, where light was coupled to the central waveguide and when sufficient power was injected, the field was localized close to the input waveguiders and its distribution was successfully described by the discrete nonlinear Schrodinger equation.
Abstract: We report the observation of discrete spatial optical solitons in an array of 41 waveguides. Light was coupled to the central waveguide. At low power, the propagating field spreads as it couples to more waveguides. When sufficient power was injected, the field was localized close to the input waveguides and its distribution was successfully described by the discrete nonlinear Schr\"odinger equation.

Journal ArticleDOI
TL;DR: In this article, it was shown that the entropy of a large non-rotating black hole is proportional to its horizon area, and that the constant of proportionality depends upon the Immirzi parameter, which fixes the spectrum of the area operator in loop quantum gravity.
Abstract: A ``black hole sector'' of nonperturbative canonical quantum gravity is introduced. The quantum black hole degrees of freedom are shown to be described by a Chern-Simons field theory on the horizon. It is shown that the entropy of a large nonrotating black hole is proportional to its horizon area. The constant of proportionality depends upon the Immirzi parameter, which fixes the spectrum of the area operator in loop quantum gravity; an appropriate choice of this parameter gives the Bekenstein-Hawking formula $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}A/4{\ensuremath{\ell}}_{P}^{2}$. With the same choice of the Immirzi parameter, this result also holds for black holes carrying electric or dilatonic charge, which are not necessarily near extremal.

Journal ArticleDOI
Tin-Lun Ho1
TL;DR: In this article, the ground states of spin-1 bosons can be either ferromagnetic or polar, depending on the scattering lengths in different angular momentum channels, and the collective modes of these states have very different spin character and spatial distributions.
Abstract: We show that in an optical trap the ground states of spin-1 bosons such as ${}^{23}\mathrm{Na}$, ${}^{39}\mathrm{K}$, and ${}^{87}\mathrm{Rb}$ can be either ferromagnetic or ``polar" states, depending on the scattering lengths in different angular momentum channels. The collective modes of these states have very different spin character and spatial distributions. While ordinary vortices are stable in the polar state, only those with unit circulation are stable in the ferromagnetic state. The ferromagnetic state also has coreless (or Skyrmion) vortices like those of ${}^{3}\mathrm{He}\ensuremath{-}A$.

Journal ArticleDOI
TL;DR: Peres as mentioned in this paper showed that if a mixed state can be distilled to the singlet form it must violate partial transposition criterion, which implies that there are two qualitatively different types of entanglement.
Abstract: It is shown that if a mixed state can be distilled to the singlet form it must violate partial transposition criterion [A. Peres, Phys. Rev. Lett. 76, 1413 (1996)]. It implies that there are two qualitatively different types of entanglement: ``free'' entanglement which is distillable, and ``bound'' entanglement which cannot be brought to the singlet form useful for quantum communication purposes. A possible physical meaning of the result is discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors experimentally entangle freely propagating particles that never physically interacted with one another or which have never been dynamically coupled by any other means, and demonstrate that quantum entanglement requires the entangled particles neither to come from a common source nor to have interacted in the past.
Abstract: We experimentally entangle freely propagating particles that never physically interacted with one another or which have never been dynamically coupled by any other means. This demonstrates that quantum entanglement requires the entangled particles neither to come from a common source nor to have interacted in the past. In our experiment we take two pairs of polarization entangled photons and subject one photon from each pair to a Bell-state measurement. This results in projecting the other two outgoing photons into an entangled state.

Journal ArticleDOI
TL;DR: In this article, the authors proposed that the observed resistance changes are due to excitations of zero-wave-number spin waves in the magnetic layers, induced by a high current density injected into the multilayer through a point contact.
Abstract: We describe variations in the resistance of $\mathrm{Co}/\mathrm{Cu}$ multilayers, induced by means of a high current density $\ensuremath{\approx}{10}^{8}\mathrm{A}/{\mathrm{cm}}^{2}$ injected into the multilayer through a point contact. We propose that the observed resistance changes are due to excitations of zero-wave-number spin waves in the magnetic layers. As predicted, such current-driven excitation of a magnetic multilayer occurs for only one direction of current flow and has a current threshold which increases linearly with the applied magnetic field.

Journal ArticleDOI
TL;DR: In this paper, a spontaneous emission rate enhancement by a factor of up to 5 was selectively observed for the QB's which are on resonance with one-cavity mode. But the effect of the random spatial and spectral distributions of the QBs was not considered.
Abstract: Semiconductor quantum boxes (QB's) are well suited to cavity quantum electrodynamic experiments in the solid state because of their sharp emission. We study by time-resolved photoluminescence InAs QB's placed in the core of small-volume and high-finesse GaAs/AlAs pillar microresonators. A spontaneous emission rate enhancement by a factor of up to 5 is selectively observed for the QB's which are on resonance with one-cavity mode. We explain its magnitude by considering the Purcell figure of merit of the micropillars and the effect of the random spatial and spectral distributions of the QB's.


Journal ArticleDOI
TL;DR: It is shown how to quantify this information, in bits, free from any assumptions about which features of the spike train or input signal are most important, and this approach is applied to the analysis of experiments on a motion sensitive neuron in the fly visual system.
Abstract: The nervous system represents time dependent signals in sequences of discrete, identical action potentials or spikes; information is carried only in the spike arrival times. We show how to quantify this information, in bits, free from any assumptions about which features of the spike train or input signal are most important, and we apply this approach to the analysis of experiments on a motion sensitive neuron in the fly visual system. This neuron transmits information about the visual stimulus at rates of up to 90 bits/s, within a factor of 2 of the physical limit set by the entropy of the spike train itself.

Journal ArticleDOI
TL;DR: In this paper, a femtosecond time-resolved Faraday rotation in the Voigt geometry was observed in a GaAs-type GaAs bulk semiconductors.
Abstract: Extended electron spin precession in $n$-type GaAs bulk semiconductors is directly observed by femtosecond time-resolved Faraday rotation in the Voigt geometry. Synchronous optical pumping of the spin system amplifies and sustains spin motion, exposing a regime where spin lifetimes increase tenfold at low fields and exceed 100 ns at zero field. Precise studies in field and temperature provide clues to the relevant electron relaxation mechanisms, indicating a strong dependence on doping concentration.

Journal ArticleDOI
TL;DR: In this paper, a metaloxide-semiconductor capacitor using SrTiO{sub 3} as an alternative to SiOthinsp{sub 2} yields the extraordinary result of t{sub eqlt}10 {Angstrom}.
Abstract: The long-standing problem of growing a commensurate crystalline oxide interface with silicon has been solved. Alkaline earth and perovskite oxides can be grown in perfect registry on the (001) face of silicon, totally avoiding the amorphous silica phase that ordinarily forms when silicon is exposed to an oxygen containing environment. The physics of the heteroepitaxy lies in establishing a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. A metal-oxide-semiconductor capacitor using SrTiO{sub 3} as an alternative to SiOthinsp{sub 2} yields the extraordinary result of t{sub eq}{lt}10 {Angstrom} . {copyright} {ital 1998} {ital The American Physical Society}

Journal ArticleDOI
TL;DR: In this paper, the formation and control of submerged fluid jets is described experimentally and theoretically, and the focusing process necessary to achieve small length scales is characterized experimentally, theoretically and empirically.
Abstract: We describe the formation and control of nanoscale, submerged fluid jets. The focusing process necessary to achieve these small length scales is characterized experimentally and theoretically. Fast mixing is one important application of nanoscale fluid control: We demonstrate this with a continuous-flow mixer capable of mix times of less than $10\ensuremath{\mu}\mathrm{s}$ and sample consumption rates of nanoliters per second. This new technique facilitates the study of fast reaction kinetics on time scales unattainable with conventional mixing technology.