47,363 research outputs found
Localization length of a soliton from a non-magnetic impurity in a general double-spin-chain model
A localization length of a free-spin soliton from a non-magnetic impurity is
deduced in a general double-spin-chain model ( model). We have
solved a variational problem which employs the nearest-neighbor singlet-dimer
basis. The wave function of a soliton is expressed by the Airy function, and
the localization length is found to obey a power law of the
dimerization with an exponent -1/3; .
This explains why NaV_2O_5 does not show the antiferromagnetic order, while
CuGeO_3 does by impurity doping. When the gap exists by the bond-dimerization,
a soliton is localized and no order is expected. Contrary, there is a
possibility of the order when the gap is mainly due to frustration.Comment: 4 pages, REVTeX, Figures are in eps-file
Ti and V layers retard interaction between Al films and polycrystalline Si
Fine-grained polycrystalline Si (poly Si) in contact with Al films recrystallizes at temperatures well below the Si-Al eutectic (577 °C). We show that this interaction can be deferred or suppressed by placing a buffer layer of Ti or V between the Al film and the poly Si. During annealing, Ti or V form TiAl3 or Val3 at the buffer-layer–Al-film interface, but do not react with the poly Si so that the integrity of the poly Si is preserved as long as some unreacted Ti or V remains. The reaction between the Ti or V layer and the Al film is transport limited ([proportional]t^1/2) and characterized by the diffusion constants 1.5×10^15 exp(–1.8eV/kT) Å^2/sec or 8.4×10^12 exp(–1.7eV/kT) Å^2/sec, respectively
Possible direct method to determine the radius of a star from the spectrum of gravitational wave signals
We computed the spectrum of gravitational waves from a dust disk star of
radius R inspiraling into a Kerr black hole of mass M and specific angular
momentum a. We found that when R is much larger than the wave length of the
quasinormal mode, the spectrum has several peaks and the separation of peaks
is proportional to irrespective of M and a. This
suggests that the radius of the star in coalescing binary black hole - star
systems may be determined directly from the observed spectrum of gravitational
wave. This also suggests that the spectrum of the radiation may give us
important information in gravitational wave astronomy as in optical astronomy.Comment: 4 pages with 3 eps figures, revtex.sty, accepted for publication in
Phys. Rev. Let
Rabi Oscillations in Landau-Quantized Graphene
We investigate the relation between the canonical model of quantum optics,
the Jaynes-Cummings Hamiltonian and Dirac fermions in quantizing magnetic
field. We demonstrate that Rabi oscillations are observable in the optical
response of graphene, providing us with a transparent picture about the
structure of optical transitions. While the longitudinal conductivity reveals
chaotic Rabi oscillations, the Hall component measures coherent ones. This
opens up the possibility of investigating a microscopic model of a few quantum
objects in a macroscopic experiment with tunable parameters.Comment: 5 pages, 4 figure
Ground-state phase diagram of the one-dimensional Hubbard-model with an alternating potential
We investigate the ground-state phase diagram of the one-dimensional
half-filled Hubbard model with an alternating potential--a model for the
charge-transfer organic materials and the ferroelectric perovskites. We
numerically determine the global phase diagram of this model using the
level-crossing and the phenomenological renormalization-group methods based on
the exact diagonalization calculations. Our results support the mechanism of
the double phase transitions between Mott and a band insulators pointed out by
Fabrizio, Gogolin, and Nersesyan [Phys. Rev. Lett. 83, 2014 (1999)]: We confirm
the existence of the spontaneously dimerized phase as an intermediate state.
Further we provide numerical evidences to check the criticalities on the phase
boundaries. Especially, we perform the finite-size-scaling analysis of the
excitation gap to show the two-dimensional Ising transition in the charge part.
On the other hand, we confirm that the dimerized phase survives in the
strong-coupling limit, which is one of the resultants of competition between
the ionicity and correlation effects.Comment: 8 pages, 8 figure
Measured Quantum Fourier Transform of 1024 Qubits on Fiber Optics
Quantum Fourier transform (QFT) is a key function to realize quantum
computers. A QFT followed by measurement was demonstrated on a simple circuit
based on fiber-optics. The QFT was shown to be robust against imperfections in
the rotation gate. Error probability was estimated to be 0.01 per qubit, which
corresponded to error-free operation on 100 qubits. The error probability can
be further reduced by taking the majority of the accumulated results. The
reduction of error probability resulted in a successful QFT demonstration on
1024 qubits.Comment: 15 pages, 6 figures, submitted to EQIS 2003 Special issue, Int. J.
Quantum Informatio
Vanishing of the negative-sign problem of quantum Monte Carlo simulations in one-dimensional frustrated spin systems
The negative-sign problem in one-dimensional frustrated quantum spin systems
is solved. We can remove negative signs of the local Boltzmann weights by using
a dimer basis that has the spin-reversal symmetry. Validity of this new basis
is checked in a general frustrated double-spin-chain system, namely the
J_0-J_1-J_2-J_3 model. The negative sign vanishes perfectly for .Comment: 4 pages, REVTeX, 4 figures in eps-file
General formulation of general-relativistic higher-order gauge-invariant perturbation theory
Gauge-invariant treatments of general-relativistic higher-order perturbations
on generic background spacetime is proposed. After reviewing the general
framework of the second-order gauge-invariant perturbation theory, we show the
fact that the linear-order metric perturbation is decomposed into
gauge-invariant and gauge-variant parts, which was the important premis of this
general framework. This means that the development the higher-order
gauge-invariant perturbation theory on generic background spacetime is
possible. A remaining issue to be resolve is also disscussed.Comment: 4 pages, no figure. (v3) some explanations are added and a reference
is adde
- …