2,269 research outputs found
Restrictions on the coherence of the ultrafast optical emission from an electron-hole pairs condensate
We report on the transfer of coherence from a quantum-well electron-hole
condensate to the light it emits. As a function of density, the coherence of
the electron-hole pair system evolves from being full for the low density
Bose-Einstein condensate to a chaotic behavior for a high density BCS-like
state. This degree of coherence is transfered to the light emitted in a damped
oscillatory way in the ultrafast regime. Additionally, the photon field
exhibits squeezing properties during the transfer time. We analyze the effect
of light frequency and separation between electron and hole layers on the
optical coherence. Our results suggest new type of ultrafast experiments for
detecting electron-hole pair condensation.Comment: 4 pages,3 figures, to be published in Physical Review Letters. Minor
change
Quantum Phase Transitions detected by a local probe using Time Correlations and Violations of Leggett-Garg Inequalities
In the present paper we introduce a way of identifying quantum phase
transitions of many-body systems by means of local time correlations and
Leggett-Garg inequalities. This procedure allows to experimentally determine
the quantum critical points not only of finite-order transitions but also those
of infinite order, as the Kosterlitz-Thouless transition that is not always
easy to detect with current methods. By means of simple analytical arguments
for a general spin- Hamiltonian, and matrix product simulations of
one-dimensional and anisotropic models, we argue that
finite-order quantum phase transitions can be determined by singularities of
the time correlations or their derivatives at criticality. The same features
are exhibited by corresponding Leggett-Garg functions, which noticeably
indicate violation of the Leggett-Garg inequalities for early times and all the
Hamiltonian parameters considered. In addition, we find that the infinite-order
transition of the model at the isotropic point can be revealed by the
maximal violation of the Leggett-Garg inequalities. We thus show that quantum
phase transitions can be identified by purely local measurements, and that
many-body systems constitute important candidates to observe experimentally the
violation of Leggett-Garg inequalities.Comment: Minor changes, 11 pages, 11 figures. Final version published in Phys.
Rev.
Crossover between the Dense Electron-Hole Phase and the BCS Excitonic Phase in Quantum Dots
Second order perturbation theory and a Lipkin-Nogami scheme combined with an
exact Monte Carlo projection after variation are applied to compute the
ground-state energy of electron-hole pairs confined in a
parabolic two-dimensional quantum dot. The energy shows nice scaling properties
as N or the confinement strength is varied. A crossover from the high-density
electron-hole phase to the BCS excitonic phase is found at a density which is
roughly four times the close-packing density of excitons.Comment: Improved variational and projection calculations. 17 pages, 3 ps
figures. Accepted for publication in Int. J. Mod. Phys.
Cannabis y sus productos : marihuana y otras yerbas
Fil: Villaamil Lepori, Edda C. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Centro de Asesoramiento Toxicológico Analítico; ArgentinaFil: Quiroga, Patricia N. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Centro de Asesoramiento Toxicológico Analítico; ArgentinaEl Cannabis sigue siendo la droga ilícita que más se produce, trafica y consume en el mundo. La\nmarihuana, producto del Cannabis, es una droga de abuso de consumo importante en nuestra sociedad,\nespecialmente en algunos sectores juveniles
Analytic results for particles with interaction in two dimensions and an external magnetic field
The -dimensional quantum problem of particles (e.g. electrons) with
interaction in a two-dimensional parabolic potential
(e.g. quantum dot) and magnetic field , reduces exactly to solving a
-dimensional problem which is independent of and . An
exact, infinite set of relative mode excitations are obtained for any . The
problem reduces to that of a ficticious particle in a two-dimensional,
non-linear potential of strength , subject to a ficticious magnetic
field , the relative angular momentum.Comment: To appear in Physical Review Letters (in press). RevTeX file. Two
figures available from [email protected] or
[email protected]
First all-sky search for continuous gravitational waves from unknown sources in binary systems
Paper producido por "The LIGO Scientific Collaboration and the Virgo Collaboration". (En el registro se mencionan solo algunos autores de las decenas de personas que participan).We present the first results of an all-sky search for continuous gravitational waves from unknown
spinning neutron stars in binary systems using LIGO and Virgo data. Using a specially developed analysis
program, the TwoSpect algorithm, the search was carried out on data from the sixth LIGO science run and
the second and third Virgo science runs. The search covers a range of frequencies from 20 Hz to 520 Hz, a
range of orbital periods from 2 to ∼2; 254 h and a frequency- and period-dependent range of frequency
modulation depths from 0.277 to 100 mHz. This corresponds to a range of projected semimajor axes of the
orbit from ∼0.6 × 10−3 ls to ∼6; 500 ls assuming the orbit of the binary is circular. While no plausible
candidate gravitational wave events survive the pipeline, upper limits are set on the analyzed data. The most
sensitive 95% confidence upper limit obtained on gravitational wave strain is 2.3 × 10−24 at 217 Hz,
assuming the source waves are circularly polarized. Although this search has been optimized for circular
binary orbits, the upper limits obtained remain valid for orbital eccentricities as large as 0.9. In addition,
upper limits are placed on continuous gravitational wave emission from the low-mass x-ray binary Scorpius
X-1 between 20 Hz and 57.25 Hz.http://journals.aps.org/prd/abstract/10.1103/PhysRevD.90.062010publishedVersionFil: Maglione, C. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Maglione, C. Argentinian Gravitational Wave Group; Argentina.Fil: Quiroga, C. Argentinian Gravitational Wave Group; Argentina.Fil: Aasi, J. LIGO. California Institute of Technology; Estados Unidos de América.Física de Partículas y Campo
Caracterización de semillas blancas y negras de Salvia hispanica L. (Lamiaceae)
Caracterización de semillas blancas y negras de Salvia hispanica L. (Lamiaceae)Fil: Bueno, Mirian. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentin
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