570 research outputs found
A single structured light beam as an atomic cloud splitter
We propose a scheme to split a cloud of cold non-interacting neutral atoms
based on their dipole interaction with a single structured light beam which
exhibits parabolic cylindrical symmetry. Using semiclassical numerical
simulations, we establish a direct relationship between the general properties
of the light beam and the relevant geometric and kinematic properties acquired
by the atomic cloud as its passes through the beam.Comment: 10 pages, 5 figure
Entanglement enhancement and postselection for two atoms interacting with thermal light
The evolution of entanglement for two identical two-level atoms coupled to a
resonant thermal field is studied for two different families of input states.
Entanglement enhancement is predicted for a well defined region of the
parameter space of one of these families. The most intriguing result is the
possibility of probabilistic production of maximally entangled atomic states
even if the input atomic state is factorized and the corresponding output state
is separable.Comment: accepted for publication in J. Phys.
Measurement of the thorium-228 activity in solutions cavitated by ultrasonic sound
We show that cavitation of a solution of thorium-228 in water does not induce
its transformation at a faster rate than the natural radioactive decay. We
measured the activity of a thorium-228 solution in water before, and after, it
was subjected to a cavitation at 44 kHz and W for 90 minutes in order to
observe any change in the thorium half-life. The results were compared to the
original activity of the sample and we observed no change. Our results and
conclusions conflict with those in a recent paper by F. Cardone et. al. [Phys.
Lett. A 373 (2009) 1956-1958].Comment: 6 pages, 1 figure, 2 tables, v1 submitted to Physics Letters A. v2:
minor corrections, change caption for tables (include comment for counter
efficiency with uncertainty) and symbols for beta-alph
Comment on "Fermionic entanglement ambiguity in noninertial frames"
In this comment we show that the ambiguity of entropic quantities calculated
in Physical Review A 83, 062323 (2011) for fermionic fields in the context of
Unruh effect is not related to the properties of anticommuting fields, as
claimed in Physical Review A 83, 062323 (2011), but rather to wrong
mathematical manipulations with them and not taking into account a fundamental
superselection rule of quantum field theory.Comment: To appear in Physical Review A. Some of the problems discussed in
this comment can also be found in other previously published papers studying
the Unruh effect for fermions (in the context of quantum information theory).
An extended version of the comment can be found here
http://arxiv.org/abs/1108.555
Quantum Mechanical Properties of Bessel Beams
Bessel beams are studied within the general framework of quantum optics. The
two modes of the electromagnetic field are quantized and the basic dynamical
operators are identified. The algebra of these operators is analyzed in detail;
it is shown that the operators that are usually associated to linear momentum,
orbital angular momentum and spin do not satisfy the algebra of the translation
and rotation group. In particular, what seems to be the spin is more similar to
the helicity. Some physical consequences of these results are examined.Comment: 17 pages, no figures. New versio
Optical scalar beam propagation in nontrivial spacetime backgrounds
We study the propagation of structured optical scalar beams in a spacetime
background parameterized by a second-rank symmetric tensor. An analytic
expression for the Green's function in a cylindrical coordinate system is
obtained for particular choices of such a tensor. This facilitates the
numerical exploration of the propagation of apertured Gaussian beams in this
nontrivial background. Unusual focusing properties are found along with a
decrease in the Gouy phase compared to that in standard vacuum. In the case of
apertured Bessel beams, the medium allows to overcome finite aperture effects
so that the corresponding diffraction length is increased; besides, the central
spot of a zero order Bessel concentrates an increased fraction of the energy of
the beam. Multiple scenarios beyond an electromagnetic field in the presence of
an anisotropic medium could support the results reported here. They include a
bosonic field in a weak gravitational field or a nontrivial spacetime
background arising from Lorentz symmetry breaking. In particular, our results
could illustrate how optically transparent multiferroic materials offer
unprecedented opportunities to tailor structured beam propagation, as well as
to simulate nontrivial spacetime backgrounds.Comment: 15 pages, 24 figure
Rotational Effects of Twisted Light on Atoms Beyond the Paraxial Approximation
The transition probability for the emission of a Bessel photon by an atomic
system is calculated within first order perturbation theory. We derive a closed
expression for the electromagnetic potentials beyond the paraxial approximation
that permits a systematic multipole approximation . The matrix elements between
center of mass and internal states are evaluated for some specially relevant
cases. This permits to clarify the feasibility of observing the rotational
effects of twisted light on atoms predicted by the calculations. It is shown
that the probability that the internal state of an atom acquires orbital
angular momentum from light is, in general, maximum for an atom located at the
axis of a Bessel mode. For a Gaussian packet, the relevant parameter is the
ratio of the spread of the atomic center of mass wave packet to the transversal
wavelength of the photon.Comment: 10 pages, no figure
Capacities of Grassmann channels
A new class of quantum channels called Grassmann channels is introduced and
their classical and quantum capacity is calculated. The channel class appears
in a study of the two-mode squeezing operator constructed from operators
satisfying the fermionic algebra. We compare Grassmann channels with the
channels induced by the bosonic two-mode squeezing operator. Among other
results, we challenge the relevance of calculating entanglement measures to
assess or compare the ability of bosonic and fermionic states to send quantum
information to uniformly accelerated frames.Comment: 33 pages, Accepted in Journal of Mathematical Physics; The role of
the (fermionic) braided tensor product for quantum Shannon theory, namely
capacity formulas, elucidated; The conclusion on the equivalence of Unruh
effect for bosons and fermions for quantum communication purposes made clear
and even more precis
Hermenéutica histórica de la formación del individuo
La hermenéutica histórica de Gadamer ha aportado elementos para la comprensión-interpretación de la situación desde la que se ven en horizonte los hilos de la tradición. El presente trabajo pretende aportar precisamente una interpretación de la formación epocal del individuo, la situación histórica en que estamos y que se ha visto frecuentemente como consecuencia inmediata de la descomposición de la época moderna. Se describe la tradición que nos ha traído a la posibilidad de ser ahora individuos, a través de un ducto histórico que es el relato. En esta propuesta se describen las tres formaciones epocales en que han devenido los relatos de la tradición cristiana. Los relatos son el medio a través del cual se pretende estudiar la formación de cada época, asumiendo que hay una analogía entre la forma general de la época y la forma tramática del relato que está legitimado en esa misma época. Así, se asume que estas formas las produce una institución a la que tienden los sentidos y es desde esa institución desde la que legitiman los relatos. En la reubicación formal de la institución, se rehacen los sentidos para nuevas formaciones epocales donde se posibilitan las formas de ser y hacer para una época. Se busca el relato que legitima al individuo en esta formación epocal que nos sitúa en la historia como individuos. En la transformación de las épocas se propone la formación epocal del individuo como punta y fin de las transformaciones de los relatos de la tradición cristiana que han quedado sin fuerza, sin posibilidades suficientes para la reformación epocal
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