21,868 research outputs found
Asymptotic analysis of the model for distribution of high-tax payers
The z-transform technique is used to investigate the model for distribution
of high-tax payers, which is proposed by two of the authors (K. Y and S. M) and
others. Our analysis shows an asymptotic power-law of this model with the
exponent -5/2 when a total ``mass'' has a certain critical value. Below the
critical value, the system exhibits an ordinary critical behavior, and scaling
relations hold. Above the threshold, numerical simulations show that a
power-law distribution coexists with a huge ``monopolized'' member. It is
argued that these behaviors are observed universally in conserved aggregation
processes, by analizing an extended model.Comment: 5pages, 3figure
Quantum Bit Regeneration
Decoherence and loss will limit the practicality of quantum cryptography and
computing unless successful error correction techniques are developed. To this
end, we have discovered a new scheme for perfectly detecting and rejecting the
error caused by loss (amplitude damping to a reservoir at T=0), based on using
a dual-rail representation of a quantum bit. This is possible because (1)
balanced loss does not perform a ``which-path'' measurement in an
interferometer, and (2) balanced quantum nondemolition measurement of the
``total'' photon number can be used to detect loss-induced quantum jumps
without disturbing the quantum coherence essential to the quantum bit. Our
results are immediately applicable to optical quantum computers using single
photonics devices.Comment: 4 pages, postscript only, figures available at
http://feynman.stanford.edu/qcom
Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II
The optical exciton Aharonov-Bohm effect, i. e. an oscillatory component in
the energy of optically active (bright) states, is investigated in nanorings.
It is shown that a small effective electron mass, strong confinement of the
electron, and high barrier for the hole, achieved e. g. by an InAs nanoring
embedded in an AlGaSb quantum well, are favorable for observing the optical
exciton Aharonov-Bohm effect. The second derivative of the exciton energy with
respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations
even for the lowest bright state unambiguously. A connection between the
theories for infinitesimal narrow and finite width rings is established.
Furthermore, the magnetization is compared to the persistent current, which
oscillates periodically with the magnetic field and confirms thus the
non-trivial (connected) topology of the wave function in the nanoring.Comment: 12 pages, 11 figure
Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. Calculating beyond the
first-order mechanism, where a nuclear spin directly interacts with spin waves
through the hyperfine coupling, we demonstrate that the
exchange-scattering-enhanced three-magnon nuclear relaxation may generally
predominate over the Raman one with increasing temperature and decreasing
field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest
that the major contribution to 1/T_1_ be made by the three-magnon scattering.Comment: 8 pages, 5 figure
Hyperonic mixing in five-baryon double-strangeness hypernuclei in a two-channel treatment
Properties of hypernuclei H and He are studied in a two-channel approach with explicit treatment of
coupling of channels ^3\text{Z}+\Lambda+\Lambda and \alpha+\Xi. Diagonal
\Lambda\Lambda and coupling \Lambda\Lambda-\Xi N interactions are derived
within G-matrix procedure from Nijmegen meson-exchange models. Bond energy
\Delta B_{\Lambda\Lambda} in He exceeds significantly
that in H due to the channel coupling. Diagonal \Xi\alpha
attraction amplifies the effect, which is sensitive also to \Lambda-core
interaction. The difference of the \Delta B_{\Lambda\Lambda} values can be an
unambiguous signature of the \Lambda\Lambda-\Xi N coupling in \Lambda\Lambda
hypernuclei. However, improved knowledge of the hyperon-nucleus potentials is
needed for quantitative extraction of the coupling strength from future data on
the \Lambda\Lambda hypernuclear binding energies.Comment: 11 pages with 3 figures; Phys. Rev. C, accepte
Electronic properties of buried hetero-interfaces of LaAlO3 on SrTiO3
We have made very thin films of LaAlO3 on TiO2 terminated SrTiO3 and have
measured the properties of the resulting interface in various ways. Transport
measurements show a maximum sheet carrier density of 1016 cm-2 and a mobility
around 104 cm2 V-1 s-1. In situ ultraviolet photoelectron spectroscopy (UPS)
indicates that for these samples a finite density of states exists at the Fermi
level. From the oxygen pressure dependence measured in both transport as well
as the UPS, we detail, as reported previously by us, that oxygen vacancies play
an important role in the creation of the charge carriers and that these
vacancies are introduced by the pulsed laser deposition process used to make
the heterointerfaces. Under the conditions studied the effect of LaAlO3 on the
carrier density is found to be minimal.Comment: 19 pages, 6 figure
Comments on discrete time in quantum mechanics
The possibility that time can be regarded as a discrete parameter is
re-examined. We study the dynamics of the free particle and find in some cases
superluminal propagation
Relaxational behavior of the infinite-range Ising spin-glass in a transverse field
We study the zero-temperature behavior of the infinite-ranged Ising spin
glass in a transverse field. Using spin summation techniques and Monte Carlo
methods we characterize the zero-temperature quantum transition. Our results
are well compatible with a value for the correlation length
exponent, for the dynamical exponent and an algebraic decay for
the imaginary-time correlation function. The zero-temperature relaxation of the
energy in the presence of the transverse field shows that the system
monotonically reaches the ground state energy due to tunneling processes and
displays strong glassy effects.Comment: 15 pages + 5 Figures, Revte
Simulating Particle Dispersions in Nematic Liquid-Crystal Solvents
A new method is presented for mesoscopic simulations of particle dispersions
in nematic liquid crystal solvents. It allows efficient first-principle
simulations of the dispersions involving many particles with many-body
interactions mediated by the solvents. A simple demonstration is shown for the
aggregation process of a two dimentional dispersion.Comment: 5 pages, 5 figure
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