935 research outputs found
Level Statistics and Localization for Two Interacting Particles in a Random Potential
We consider two particles with a local interaction in a random potential
at a scale (the one particle localization length). A simplified
description is provided by a Gaussian matrix ensemble with a preferential
basis. We define the symmetry breaking parameter
associated to the statistical invariance under change of basis. We show that
the Wigner-Dyson rigidity of the energy levels is maintained up to an energy
. We find that when (the
inverse lifetime of the states of the preferential basis) is smaller than
(the level spacing), and when . This implies that the two-particle localization length first
increases as before eventually behaving as .Comment: 4 pages REVTEX, 4 Figures EPS, UUENCODE
Emergence of Quantum Ergodicity in Rough Billiards
By analytical mapping of the eigenvalue problem in rough billiards on to a
band random matrix model a new regime of Wigner ergodicity is found. There the
eigenstates are extended over the whole energy surface but have a strongly
peaked structure. The results of numerical simulations and implications for
level statistics are also discussed.Comment: revtex, 4 pages, 4 figure
Properties of the chiral spin liquid state in generalized spin ladders
We study zero temperature properties of a system of two coupled quantum spin
chains subject to fields explicitly breaking time reversal symmetry and parity.
Suitable choice of the strength of these fields gives a model soluble by Bethe
Ansatz methods which allows to determine the complete magnetic phase diagram of
the system and the asymptotics of correlation functions from the finite size
spectrum. The chiral properties of the system for both the integrable and the
nonintegrable case are studied using numerical techniques.Comment: 19 pages, 9eps figures, Late
Quantum error correction of coherent errors by randomization
A general error correction method is presented which is capable of correcting
coherent errors originating from static residual inter-qubit couplings in a
quantum computer. It is based on a randomization of static imperfections in a
many-qubit system by the repeated application of Pauli operators which change
the computational basis. This Pauli-Random-Error-Correction (PAREC)-method
eliminates coherent errors produced by static imperfections and increases
significantly the maximum time over which realistic quantum computations can be
performed reliably. Furthermore, it does not require redundancy so that all
physical qubits involved can be used for logical purposes.Comment: revtex 4 pages, 3 fig
Coherent propagation of interacting particles in a random potential: the Mechanism of enhancement
Coherent propagation of two interacting particles in weak random
potential is considered. An accurate estimate of the matrix element of
interaction in the basis of localized states leads to mapping onto the relevant
matrix model. This mapping allows to clarify the mechanism of enhancement of
the localization length which turns out to be rather different from the one
considered in the literature. Although the existence of enhancement is
transparent, an analytical solution of the matrix model was found only for very
short samples. For a more realistic situation numerical simulations were
performed. The result of these simulations is consistent with l_{2}/l_1 \sim
l_1^{\gamma} , where and are the single and two particle
localization lengths and the exponent depends on the strength of the
interaction. In particular, in the limit of strong particle-particle
interaction there is no enhancement of the coherent propagation at all ().Comment: 23 pages, REVTEX, 3 eps figures, improved version accepted for
publication in Phys. Rev.
Persistent currents in diffusive metallic cavities: Large values and anomalous scaling with disorder
The effect of disorder on confined metallic cavities with an Aharonov-Bohm
flux line is addressed. We find that, even deep in the diffusive regime, large
values of persistent currents may arise for a wide variety of geometries. We
present numerical results supporting an anomalous scaling law of the average
typical current with the strength of disorder , with . This is contrasted with previously
reported results obtained for cylindrical samples where a scaling has been found. Possible links to, up to date, unexplained
experimental data are finally discussed.Comment: 5 pages, 4 figure
Thermodynamics of an integrable model for electrons with correlated hopping
A new supersymmetric model for electrons with generalized hopping terms and
Hubbard interaction on a one-dimensional lattice is solved by means of the
Bethe Ansatz. We investigate the phase diagram of this model by studying the
ground state and excitations of the model as a function of the interaction
parameter, electronic density and magnetization. Using arguments from conformal
field theory we can study the critical exponents describing the asymptotic
behaviour of correlation functions at long distances.Comment: 24 pp., latex+epsf, figures include
Doping Induced Magnetization Plateaus
The low temperature magnetization process of antiferromagnetic spin-S chains
doped with mobile spin-(S-1/2) carriers is studied in an exactly solvable
model. For sufficiently high magnetic fields the system is in a metallic phase
with a finite gap for magnetic excitations. In this phase which exists for a
large range of carrier concentrations x the zero temperature magnetization is
determined by x alone. This leads to plateaus in the magnetization curve at a
tunable fraction of the saturation magnetization. The critical behaviour at the
edges of these plateaus is studied in detail.Comment: RevTeX, 4 pp. incl. 3 figure
Critical exponents of the degenerate Hubbard model
We study the critical behaviour of the \SUN{} generalization of the
one-dimensional Hubbard model with arbitrary degeneracy . Using the
integrability of this model by Bethe Ansatz we are able to compute the spectrum
of the low-lying excitations in a large but finite box for arbitrary values of
the electron density and of the Coulomb interaction. This information is used
to determine the asymptotic behaviour of correlation functions at zero
temperature in the presence of external fields lifting the degeneracy. The
critical exponents depend on the system parameters through a
dressed charge matrix implying the relevance of the interaction of charge- and
spin-density waves.Comment: 18 page
Time evolution of Wikipedia network ranking
We study the time evolution of ranking and spectral properties of the Google
matrix of English Wikipedia hyperlink network during years 2003 - 2011. The
statistical properties of ranking of Wikipedia articles via PageRank and
CheiRank probabilities, as well as the matrix spectrum, are shown to be
stabilized for 2007 - 2011. A special emphasis is done on ranking of Wikipedia
personalities and universities. We show that PageRank selection is dominated by
politicians while 2DRank, which combines PageRank and CheiRank, gives more
accent on personalities of arts. The Wikipedia PageRank of universities
recovers 80 percents of top universities of Shanghai ranking during the
considered time period.Comment: 10 pages, 11 figures. Accepted for publication in EPJ
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