950 research outputs found
Simulating quantum-optical phenomena with cold atoms in optical lattices
We propose a scheme involving cold atoms trapped in optical lattices to
observe different phenomena traditionally linked to quantum-optical systems.
The basic idea consists of connecting the trapped atomic state to a non-trapped
state through a Raman scheme. The coupling between these two types of atoms
(trapped and free) turns out to be similar to that describing light-matter
interaction within the rotating-wave approximation, the role of matter and
photons being played by the trapped and free atoms, respectively. We explain in
particular how to observe phenomena arising from the collective spontaneous
emission of atomic and harmonic oscillator samples such as superradiance and
directional emission. We also show how the same setup can simulate Bose-Hubbard
Hamiltonians with extended hopping as well as Ising models with long-range
interactions. We believe that this system can be realized with state of the art
technology
Many-body theory of the quantum mirage
In recent scanning tunneling microscopy experiments, confinement in an
elliptical corral has been used to project the Kondo effect from one focus to
the other one. I solve the Anderson model at arbitrary temperatures, for an
impurity hybridized with eigenstates of an elliptical corral, each of which has
a resonant level width delta. This width is crucial. If delta < 20 meV, the
Kondo peak disappears, while if delta > 80 meV, the mirage disappears. For
particular conditions, a stronger mirage with the impurity out of the foci is
predicted.Comment: 5 pages, 5 figures. Some clarifications of the method added, and a
reference included to show that the hybridization of the impurity with bulk
states can be neglecte
Dynamics of the excitations of a quantum dot in a microcavity
We study the dynamics of a quantum dot embedded in a three-dimensional
microcavity in the strong coupling regime in which the quantum dot exciton has
an energy close to the frequency of a confined cavity mode. Under the
continuous pumping of the system, confined electron and hole can recombine
either by spontaneous emission through a leaky mode or by stimulated emission
of a cavity mode that can escape from the cavity. The numerical integration of
a master equation including all these effects gives the dynamics of the density
matrix. By using the quantum regression theorem, we compute the first and
second order coherence functions required to calculate the photon statistics
and the spectrum of the emitted light. Our main result is the determination of
a range of parameters in which a state of cavity modes with poissonian or
sub-poissonian (non-classical) statistics can be built up within the
microcavity. Depending on the relative values of pumping and rate of stimulated
emission, either one or two peaks close to the excitation energy of the dot
and/or to the natural frequency of the cavity are observed in the emission
spectrum. The physics behind these results is discussed
Inducing nonclassical lasing via periodic drivings in circuit quantum electrodynamics
We show how a pair of superconducting qubits coupled to a microwave cavity mode can be used to engineer a single-atom laser that emits light into a nonclassical state. Our scheme relies on the dressing of the qubit-field coupling by periodic modulations of the qubit energy. In the dressed basis, the radiative decay of the first qubit becomes an effective incoherent pumping mechanism that injects energy into the system, hence turning dissipation to our advantage. A second, auxiliary qubit is used to shape the decay within the cavity, in such a way that lasing occurs in a squeezed basis of the cavity mode. We characterize the system both by mean-field theory and exact calculations. Our work may find applications in the generation of squeezing and entanglement in circuit QED, as well as in the study of dissipative few- and many-body phase transitions
Microscopic theory for quantum mirages in quantum corrals
Scanning tunneling microscopy permits to image the Kondo resonance of a
single magnetic atom adsorbed on a metallic surface. When the magnetic impurity
is placed at the focus of an elliptical quantum corral, a Kondo resonance has
been recently observed both on top of the impurity and on top of the focus
where no magnetic impurity is present. This projection of the Kondo resonance
to a remote point on the surface is referred to as quantum mirage. We present a
quantum mechanical theory for the quantum mirage inside an ideal quantum corral
and predict that the mirage will occur in corrals with shapes other than
elliptical
Interaction between Kondo impurities in a quantum corral
We calculate the spectral densities for two impurities inside an elliptical
quantum corral using exact diagonalization in the relevant Hilbert subspace and
embedding into the rest of the system. For one impurity, the space and energy
dependence of the change in differential conductance observed
in the quantum mirage experiment is reproduced. In presence of another
impurity, is very sensitive to the hybridization between
impurity and bulk. The impurities are correlated ferromagnetically between
them. A hopping eV between impurities destroy the Kondo
resonance.Comment: 4 pages, 4 figure
Alteraciones y signos identificados por los cuidadores de niños de dos a cinco años con infección respiratoria aguda que los llevan a consultar al servicio de urgencias de 2014
La IRA se considera una de las principales causas de morbi-mortalidad en el mundo, por lo que se debe tener en cuenta que es un problema en salud pĂşblica en la que los profesionales de enfermerĂa tienen un papel fundamental, ya que se estima un promedio de 4.000.000 de muertes por año, de las cuales 1,9 millones suceden en los menores de cinco años. La prevenciĂłn y atenciĂłn temprana de esta constituye un gran desafĂo, ya que la mayorĂa de los cuidadores de los niños consultan de forma tardĂa al centro de salud, debido a que muchas veces los cuidadores no reconocen adecuadamente los signos y sĂntomas de este tipo de infecciones, por lo cual se deja avanzar el problema y este puede llegar a complicarse. A partir de lo anterior, esta investigaciĂłn busco indagar sobre los conocimientos que tienen los padres y/o cuidadores de niños menores de 5 años del concepto de IRA, los signos y alteraciones de la IRA y los razones por las cuales los llevan a consultar a un servicio de salud, con el fin de brindar pautas teĂłricas a profesionales de enfermerĂa y que desde su rol de educadores diseñen intervenciones educativas, con base en los conocimientos reales de los padres y cuidadores en la temática, con el fin de promover una consulta oportuna a los servicios de salud y asĂ disminuir complicaciones.The ARI is considered one of the leading causes of morbidity and mortality worldwide, so you should consider that it is a public health problem in which nurses have key roles as an average of 4,000,000 deaths estimated per year, of which 1.9 million happen in children under five years. Prevention and early treatment of this is a major challenge, since the most caregivers of children belatedly consult the health center because caregivers often do not adequately recognize the signs and symptoms of these infections, so it is allowed to proceed the problem and this can get complicated. From the above, this research investigate seek knowledgeof parents and / or caregivers of children under five years of the concept of ARI, signs and alterations ARI and why take them to consult a health service, in order to provide theoretical guidelines for professionals nursing and in their role as educators to design educational interventions based on actual knowledge of parents and caregivers in the field, in order to promote a proper consultation of health services and thus reduce complications.Enfermero (a)Pregrad
Quantum gases in trimerized kagom\'e lattices
We study low temperature properties of atomic gases in trimerized optical
kagom\'{e} lattices. The laser arrangements that can be used to create these
lattices are briefly described. We also present explicit results for the
coupling constants of the generalized Hubbard models that can be realized in
such lattices. In the case of a single component Bose gas the existence of a
Mott insulator phase with fractional numbers of particles per trimer is
verified in a mean field approach. The main emphasis of the paper is on an
atomic spinless interacting Fermi gas in the trimerized kagom\'{e} lattice with
two fermions per site. This system is shown to be described by a quantum spin
1/2 model on the triangular lattice with couplings that depend on the bond
directions. We investigate this model by means of exact diagonalization. Our
key finding is that the system exhibits non-standard properties of a quantum
spin-liquid crystal: it combines planar antiferromagnetic order in the ground
state with an exceptionally large number of low energy excitations. The
possibilities of experimental verification of our theoretical results are
critically discussed.Comment: 19 pages/14 figures, version to appear in Phys. Rev. A., numerous
minor corrections with respect to former lanl submissio
First detection of acceleration and deceleration in protostellar Jets? Time variability in the Chamaeleontis II outflows
Context. Kinematical and time variability studies of protostellar jets are fundamental for understanding the dynamics and the physics of these objects. Such studies remain very sporadic, since they require long baselines before they can be accomplished. Alms. We present for the first time a multi-epoch (20 years baseline) kinematical investigation of HH 52, 53, and 54 at optical and near-IR wavelengths, along with medium (optical) and high resolution (NIR) spectroscopic analyses, probing the kinematical and physical time variability conditions of the gas along the flows. Methods. By means of multi-epoch and multi-wavelength narrow-band images, we derived proper motions (PMs), tangential velocities, velocity and flux variability of the knots. Radial velocities and physical parameters of the gas were derived from spectroscopy. Finally, spatial velocities and inclination of the flows were obtained by combining both imaging and spectroscopy. Results. The PM analysis reveals three distinct, partially overlapping outflows. Spatial velocities of the knots vary from 50 km s -1 to 120 km s-1. The inclinations of the three flows are 58 ± 3°, 84 ± 2°, and 67 ± 3° (HH 52, HH 53, and HH 54 flows, respectively). In 20 years, about 60% of the observed knots show some degree of flux variability. Our set of observations apparently indicates acceleration and deceleration in a variety of knots along the jets. For about 20% of the knots, mostly coincident with working surfaces or interacting knots along the flows, a relevant variability in both flux and velocity is observed. We argue that both variabilities are related and that all or part of the kinetic energy lost by the interacting knots is successively radiated. The physical parameters derived from the diagnostics are quite homogeneous along and among the three outflows. The analysis indicates the presence of very light (NH � 103 cm-3), ionised (Te,. � 0.2-0.6), and hot (Te � 14000-26000 K) flows, impacting a denser medium. Several knots are deflected, especially in the HH 52 flow. At least for a couple of them (HH 54 G and GO), the deflection originates from the collision of the two. For the more massive parts of the flow, the deflection is likely the result of the flow collision with a dense cloud or with clumps. Finally, we discuss the possible driving sources of the flows. ©ESO 2009
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