316,537 research outputs found
The capacity of the noisy quantum channel
An upper limit is given to the amount of quantum information that can be
transmitted reliably down a noisy, decoherent quantum channel. A class of
quantum error-correcting codes is presented that allow the information
transmitted to attain this limit. The result is the quantum analog of Shannon's
bound and code for the noisy classical channel.Comment: 19 pages, Submitted to Science. Replaced give correct references to
work of Schumacher, to add a figure and an appendix, and to correct minor
mistake
Observability of the Bulk Casimir Effect: Can the Dynamical Casimir Effect be Relevant to Sonoluminescence?
The experimental observation of intense light emission by acoustically
driven, periodically collapsing bubbles of air in water (sonoluminescence) has
yet to receive an adequate explanation. One of the most intriguing ideas is
that the conversion of acoustic energy into photons occurs quantum
mechanically, through a dynamical version of the Casimir effect. We have argued
elsewhere that in the adiabatic approximation, which should be reliable here,
Casimir or zero-point energies cannot possibly be large enough to be relevant.
(About 10 MeV of energy is released per collapse.) However, there are
sufficient subtleties involved that others have come to opposite conclusions.
In particular, it has been suggested that bulk energy, that is, simply the
naive sum of , which is proportional to the volume, could
be relevant. We show that this cannot be the case, based on general principles
as well as specific calculations. In the process we further illuminate some of
the divergence difficulties that plague Casimir calculations, with an example
relevant to the bag model of hadrons.Comment: 13 pages, REVTe
DMRG and the Two Dimensional t-J Model
We describe in detail the application of the recent non-Abelian Density
Matrix Renormalization Group (DMRG) algorithm to the two dimensional t-J model.
This extension of the DMRG algorithm allows us to keep the equivalent of twice
as many basis states as the conventional DMRG algorithm for the same amount of
computational effort, which permits a deeper understanding of the nature of the
ground state.Comment: 16 pages, 3 figures. Contributed to the 2nd International Summer
School on Strongly Correlated Systems, Debrecen, Hungary, Sept. 200
Gap solitons in Bragg gratings with a harmonic superlattice
Solitons are studied in a model of a fiber Bragg grating (BG) whose local
reflectivity is subjected to periodic modulation. The superlattice opens an
infinite number of new bandgaps in the model's spectrum. Averaging and
numerical continuation methods show that each gap gives rise to gap solitons
(GSs), including asymmetric and double-humped ones, which are not present
without the superlattice.Computation of stability eigenvalues and direct
simulation reveal the existence of completely stable families of fundamental
GSs filling the new gaps - also at negative frequencies, where the ordinary GSs
are unstable. Moving stable GSs with positive and negative effective mass are
found too.Comment: 7 pages, 3 figures, submitted to EP
Planck Scale Physics of the Single Particle Schr\"{o}dinger Equation with Gravitational Self-Interaction
We consider the modification of a single particle Schr\"{o}dinger equation by
the inclusion of an additional gravitational self-potential term which follows
from the prescription that the' mass-density'that enters this term is given by
, where is the wavefunction and
is the mass of the particle. This leads to a nonlinear equation, the '
Newton Schrodinger' equation, which has been found to possess stationary
self-bound solutions, whose energy can be determined exactly using an
asymptotic method. We find that such a particle strongly violates superposition
and becomes a black hole as its mass approaches the Planck mass.Comment: 16 pages, Revtex, No figure, Submitted to Physics Letters
String Method for the Study of Rare Events
We present a new and efficient method for computing the transition pathways,
free energy barriers, and transition rates in complex systems with relatively
smooth energy landscapes. The method proceeds by evolving strings, i.e. smooth
curves with intrinsic parametrization whose dynamics takes them to the most
probable transition path between two metastable regions in the configuration
space. Free energy barriers and transition rates can then be determined by
standard umbrella sampling technique around the string. Applications to
Lennard-Jones cluster rearrangement and thermally induced switching of a
magnetic film are presented.Comment: 4 pages, 4 figure
Analysis of hadronic invariant mass spectrum in inclusive charmless semileptonic B decays
We make an analysis of the hadronic invariant mass spectrum in inclusive
charmless semileptonic B meson decays in a QCD-based approach. The decay width
is studied as a function of the invariant mass cut. We examine their
sensitivities to the parameters of the theory. The theoretical uncertainties in
the determination of from the hadronic invariant mass spectrum are
investigated. A strategy for improving the theoretical accuracy in the value of
is described.Comment: 13 pages, 5 Postscript figure
Spherically symmetric space-time with the regular de Sitter center
The requirements are formulated which lead to the existence of the class of
globally regular solutions to the minimally coupled GR equations which are
asymptotically de Sitter at the center. The brief review of the resulting
geometry is presented. The source term, invariant under radial boots, is
classified as spherically symmetric vacuum with variable density and pressure,
associated with an r-dependent cosmological term, whose asymptotic in the
origin, dictated by the weak energy condition, is the Einstein cosmological
term. For this class of metrics the ADM mass is related to both de Sitter
vacuum trapped in the origin and to breaking of space-time symmetry. In the
case of the flat asymptotic, space-time symmetry changes smoothly from the de
Sitter group at the center to the Lorentz group at infinity. Dependently on
mass, de Sitter-Schwarzschild geometry describes a vacuum nonsingular black
hole, or G-lump - a vacuum selfgravitating particlelike structure without
horizons. In the case of de Sitter asymptotic at infinity, geometry is
asymptotically de Sitter at both origin and infinity and describes, dependently
on parameters and choice of coordinates, a vacuum nonsingular cosmological
black hole, selfgravitating particlelike structure at the de Sitter background
and regular cosmological models with smoothly evolving vacuum energy density.Comment: Latex, 10 figures, extended version of the plenary talk at V
Friedmann Intern. Conf. on Gravitation and Cosmology, Brazil 2002, to appear
in Int.J.Mod.Phys.
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure
The neutron halo of He in a microscopic model
The two--neutron separation energy of He has been reproduced for the
first time in a realistic parameter--free microscopic multicluster model
comprising the and clusterizations, with cluster
breathing excitations included. The contribution of the channel is
substantial. A very thick (0.85 fm) neutron halo has been found in full
agreement with the results of the latest phenomenological analysis.Comment: Submitted to Phys. Rev. C, 8 pages, Latex with Revtex, 2 figures (not
included) available on request, 08-03-9
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