2,423 research outputs found
Pulse-splitting in light propagation through -type atomic media due to an interplay of Kerr-nonlinearity and group velocity dispersion
We investigate the spatio-temporal evolution of a Gaussian probe pulse
propagating through a four-level -type atomic medium. At two-photon
resonance of probe-and control fields, weaker probe pulses may propagate
through the medium with low absorption and pulse shape distortion. In contrast,
we find that increasing the probe pulse intensity leads to a splitting of the
initially Gaussian pulse into a sequence of subpulses in the time domain. The
number of subpulses arising throughout the propagation can be controlled via a
suitable choice of the probe and control field parameters. Employing a simple
theoretical model for the nonlinear pulse propagation, we conclude that the
splitting occurs due to an interplay of Kerr nonlinearity and group velocity
dispersion.Comment: 9 pages, 7 figure
Integer Quantum Hall Transition and Random SU(N) Rotation
We reduce the problem of integer quantum Hall transition to a random rotation
of an N-dimensional vector by an su(N) algebra, where only N specially selected
generators of the algebra are nonzero. The group-theoretical structure revealed
in this way allows us to obtain a new series of conservation laws for the
equation describing the electron density evolution in the lowest Landau level.
The resulting formalism is particularly well suited to numerical simulations,
allowing us to obtain the critical exponent \nu numerically in a very simple
way. We also suggest that if the number of nonzero generators is much less than
N, the same model, in a certain intermediate time interval, describes
percolating properties of a random incompressible steady two-dimensional flow.
In other words, quantum Hall transition in a very smooth random potential
inherits certain properties of percolation.Comment: 4 pages, 1 figur
Photon scattering from strongly driven atomic ensembles
The second order correlation function for light emitted from a strongly and
near-resonantly driven dilute cloud of atoms is discussed. Because of the
strong driving, the fluorescence spectrum separates into distinct peaks, for
which the spectral properties can be defined individually. It is shown that the
second-order correlations for various combinations of photons from different
spectral lines exhibit bunching together with super- or sub-Poissonian photon
statistics, tunable by the choice of the detector positions. Additionally, a
Cauchy-Schwarz inequality is violated for photons emitted from particular
spectral bands. The emitted light intensity is proportional to the square of
the number of particles, and thus can potentially be intense. Three different
averaging procedures to model ensemble disorder are compared.Comment: 7 pages, 4 figure
Snapshots of the EYES project
The EYES project (IST-2001-34734) is a three years European research project on self-organizing and collaborative energy-efficient sensor networks. It addresses the convergence of distributed information processing, wireless communications, and mobile computing. The goal of the project is to develop the architecture and the technology which enables the creation of a new generation of sensors that can effectively network together so as to provide a flexible platform for the support of a large variety of mobile sensor network applications. This paper provides a broad overview of the EYES project and highlights some approaches and results of the architecture
Quantum Hall Transition in the Classical Limit
We study the quantum Hall transition using the density-density correlation
function. We show that in the limit h->0 the electron density moves along the
percolating trajectories, undergoing normal diffusion. The localization
exponent coincides with its percolation value \nu=4/3. The framework provides a
natural way to study the renormalization group flow from percolation to quantum
Hall transition. We also confirm numerically that the critical conductivity of
a classical limit of quantum Hall transition is \sigma_{xx} = \sqrt{3}/4.Comment: 8 pages, 4 figures; substantial changes include the critical
conductivity calculatio
Exact relations between multifractal exponents at the Anderson transition
Two exact relations between mutlifractal exponents are shown to hold at the
critical point of the Anderson localization transition. The first relation
implies a symmetry of the multifractal spectrum linking the multifractal
exponents with indices . The second relation
connects the wave function multifractality to that of Wigner delay times in a
system with a lead attached.Comment: 4 pages, 3 figure
Density of states in graphene with vacancies: midgap power law and frozen multifractality
The density of states (DoS), , of graphene is investigated
numerically and within the self-consistent T-matrix approximation (SCTMA) in
the presence of vacancies within the tight binding model. The focus is on
compensated disorder, where the concentration of vacancies, and
, in both sub-lattices is the same. Formally, this model belongs to
the chiral symmetry class BDI. The prediction of the non-linear sigma-model for
this class is a Gade-type singularity . Our numerical data is compatible with this
result in a preasymptotic regime that gives way, however, at even lower
energies to , . We take this finding as an evidence that similar to the case
of dirty d-wave superconductors, also generic bipartite random hopping models
may exhibit unconventional (strong-coupling) fixed points for certain kinds of
randomly placed scatterers if these are strong enough. Our research suggests
that graphene with (effective) vacancy disorder is a physical representative of
such systems.Comment: References updated onl
Nuclear quantum optics with x-ray laser pulses
The direct interaction of nuclei with super-intense laser fields is studied.
We show that present and upcoming high-frequency laser facilities, especially
together with a moderate acceleration of the target nuclei, do allow for
resonant laser-nucleus interaction. These direct interactions may be utilized
for the optical measurement of nuclear properties such as the transition
frequency and the dipole moment, thus opening the field of nuclear quantum
optics. As ultimate goal, one may hope that direct laser-nucleus interactions
could become a versatile tool to enhance preparation, control and detection in
nuclear physics.Comment: 5 pages, 3 eps figures, revised versio
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