18,036 research outputs found
Nucleon excited states on the lattice
We study the pion-nucleon system in s-wave in the framework of lattice QCD in
order to gain new information on the nucleon excited states. We perform
simulations for mass degenerate light quarks at a pion mass of 266
MeV. The results show that including the two-particle states drastically
changes the energy levels. The variational analysis and the distillation
approach play an important role in the extraction of the energy levels. The
phase shift analysis allows to extract information on the resonance nature of
the observed states.Comment: 6 pages, 2 figures, talk presented at Excited QCD 2013, Bjelasnica
Mountain, Sarajev
Coherent-feedback quantum control with a dynamic compensator
I present an experimental realization of a coherent-feedback control system
that was recently proposed for testing basic principles of linear quantum
stochastic control theory [M. R. James, H. I. Nurdin and I. R. Petersen, to
appear in IEEE Transactions on Automatic Control (2008),
arXiv:quant-ph/0703150v2]. For a dynamical plant consisting of an optical
ring-resonator, I demonstrate ~ 7 dB broadband disturbance rejection of
injected laser signals via all-optical feedback with a tailored dynamic
compensator. Comparison of the results with a transfer function model pinpoints
critical parameters that determine the coherent-feedback control system's
performance.Comment: 4 pages, 4 EPS figure
Effects of electron coupling to intra- and inter-molecular vibrational modes on the transport properties of single crystal organic semiconductors
Electron coupling to intra- and inter-molecular vibrational modes is
investigated in models appropriate to single crystal organic semiconductors,
such as oligoacenes. Focus is on spectral and transport properties of these
systems beyond perturbative approaches. The interplay between different
couplings strongly affects the temperature band renormalization that is the
result of a subtle equilibrium between opposite tendencies: band narrowing due
to interaction with local modes, band widening due to electron coupling to non
local modes. The model provides an accurate description of the mobility as
function of temperature: indeed, it has the correct order of magnitude, at low
temperatures, it scales as a power-law with the exponent
larger than unity, and, at high temperatures, shows an hopping behavior with a
small activation energy.Comment: 3 Figures, Submitte
Transmission of a Symmetric Light Pulse through a Wide QW
The reflection, transmission and absorption of a symmetric electromagnetic
pulse, which carrying frequency is close to the frequency of an interband
transition in a QW (QW), are obtained. The energy levels of a QW are assumed
discrete, one exited level is taken into account. The case of a wide QW is
considered when a length of the pulse wave, appropriate to the carrying
frequency, is comparable to the QW's width. In figures the time dependencies of
the dimensionless reflection, absorption are transmission are represented. It
is shown, that the spatial dispersion and a distinction in refraction indexes
influence stronger reflection.Comment: 8 pages,8 figures with caption
Effect of the Spatial Dispersion on the Shape of a Light Pulse in a Quantum Well
Reflectance, transmittance and absorbance of a symmetric light pulse, the
carrying frequency of which is close to the frequency of interband transitions
in a quantum well, are calculated. Energy levels of the quantum well are
assumed discrete, and two closely located excited levels are taken into
account. A wide quantum well (the width of which is comparable to the length of
the light wave, corresponding to the pulse carrying frequency) is considered,
and the dependance of the interband matrix element of the momentum operator on
the light wave vector is taken into account. Refractive indices of barriers and
quantum well are assumed equal each other. The problem is solved for an
arbitrary ratio of radiative and nonradiative lifetimes of electronic
excitations. It is shown that the spatial dispersion essentially affects the
shapes of reflected and transmitted pulses. The largest changes occur when the
radiative broadening is close to the difference of frequencies of interband
transitions taken into account.Comment: 7 pages, 5 figure
Interplay between electron-phonon couplings and disorder strength on the transport properties of organic semiconductors
The combined effect of bulk and interface electron-phonon couplings on the
transport properties is investigated in a model for organic semiconductors
gated with polarizable dielectrics. While the bulk electron-phonon interaction
affects the behavior of mobility in the coherent regime below room temperature,
the interface coupling is dominant for the activated high contribution of
localized polarons. In order to improve the description of the transport
properties, the presence of disorder is needed in addition to electron-phonon
couplings. The effects of a weak disorder largely enhance the activation
energies of mobility and induce the small polaron formation at lower values of
electron-phonon couplings in the experimentally relevant window . The results are discussed in connection with experimental data of rubrene
organic field-effect transistors.Comment: 4 pages, 3 figure
Elastic Light Scattering by Semiconductor Quantum Dots
Elastic light scattering by low-dimensional semiconductor objects is
investigated theoretically. The differential cross section of resonant light
scattering on excitons in quantum dots is calculated. The polarization and
angular distribution of scattered light do not depend on the quantum-dot form,
sizes and potential configuration if light wave lengths exceed considerably the
quantum-dot size. In this case the magnitude of the total light scattering
cross section does not depend on quantum-dot sizes. The resonant total light
scattering cross section is about a square of light wave length if the exciton
radiative broadening exceeds the nonradiative broadening. Radiative broadenings
are calculated
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