25,901 research outputs found
Off-axis retrieval of orbital angular momentum of light stored in cold atoms
We report on the storage of orbital angu- lar momentum (OAM) of light of a
Laguerre-Gaussian mode in an ensemble of cold cesium atoms and its re- trieval
along an axis different from the incident light beam. We employed a
time-delayed four-wave mixing configuration to demonstrate that at small angle
(2o), after storage, the retrieved beam carries the same OAM as the one encoded
in the input beam. A calculation based on mode decomposition of the retrieved
beam over the Laguerre-Gaussian basis is in agreement with the experimental
observations done at small angle values. However, the calculation shows that
the OAM retrieving would get lost at larger angles, reducing the fidelity of
such storing-retrieving process. In addition, we have also observed that by
applying an external magnetic field to the atomic ensemble the retrieved OAM
presents Larmor oscillations, demonstrating the possibility of its manipulation
and off-axis retrieval.Comment: 9 pages, 4 figure
Evidence for deuterium astration in the planetary nebula Sh2-216?
We present FUSE observations of the line of sight to WD0439+466 (LS V +46
21), the central star of the old planetary nebula Sh2-216. The FUSE data shows
absorption by many interstellar and stellar lines, in particular D I, H2 (J = 0
- 9), HD (J = 0 - 1), and CO. Many other stellar and ISM lines are detected in
the STIS E140M HST spectra of this sightline, which we use to determine N(HI).
We derive, for the neutral gas, D/H=(0.76 +0.12 -0.11)E-5, O/H = (0.89 +0.15
-0.11)E-4 and N/H = (3.24 +0.61-0.55)E-5. We argue that most of the gas along
this sightline is associated with the planetary nebula. The low D/H ratio is
likely the result of this gas being processed through the star (astrated) but
not mixed with the ISM. This would be the first time that the D/H ratio has
been measured in predominantly astrated gas. The O/H and N/H ratios derived
here are lower than typical values measured in other planetary nebulae likely
due to unaccounted for ionization corrections.Comment: Accepted for publication is ApJ
The Stability of Quantum Concatenated Code Hamiltonians
Protecting quantum information from the detrimental effects of decoherence
and lack of precise quantum control is a central challenge that must be
overcome if a large robust quantum computer is to be constructed. The
traditional approach to achieving this is via active quantum error correction
using fault-tolerant techniques. An alternative to this approach is to engineer
strongly interacting many-body quantum systems that enact the quantum error
correction via the natural dynamics of these systems. Here we present a method
for achieving this based on the concept of concatenated quantum error
correcting codes. We define a class of Hamiltonians whose ground states are
concatenated quantum codes and whose energy landscape naturally causes quantum
error correction. We analyze these Hamiltonians for robustness and suggest
methods for implementing these highly unnatural Hamiltonians.Comment: 18 pages, small corrections and clarification
Critical phenomena of collapsing massless scalar wave packets
An analytical model that represents the collapse of a massless scalar wave
packet with continuous self-similarity is constructed, and critical phenomena
are found. In the supercritical case, the mass of black holes is finite and has
the form , with .Comment: Latex file, including 2 figures, avalaible upon reques
Self-Similar Collapse of Scalar Field in Higher Dimensions
This paper constructs continuously self-similar solution of a spherically
symmetric gravitational collapse of a scalar field in n dimensions. The
qualitative behavior of these solutions is explained, and closed-form answers
are provided where possible. Equivalence of scalar field couplings is used to
show a way to generalize minimally coupled scalar field solutions to the model
with general coupling.Comment: RevTex 3.1, 15 pages, 3 figures; references adde
Supersymmetrization of the Radiation Damping
We construct a supersymmetrized version of the model to the radiation damping
\cite{03} introduced by the present authors \cite{ACWF}. We dicuss its
symmetries and the corresponding conserved Noether charges. It is shown this
supersymmetric version provides a supersymmetric generalization of the Galilei
algebra obtained in \cite{ACWF}. We have shown that the supersymmetric action
can be splited into dynamically independent external and internal sectors.Comment: 9 page
Hidden Consequence of Active Local Lorentz Invariance
In this paper we investigate a hidden consequence of the hypothesis that
Lagrangians and field equations must be invariant under active local Lorentz
transformations. We show that this hypothesis implies in an equivalence between
spacetime structures with several curvature and torsion possibilities.Comment: Some misprints appearing in the published version have been correcte
Scattering and self-adjoint extensions of the Aharonov-Bohm hamiltonian
We consider the hamiltonian operator associated with planar sec- tions of
infinitely long cylindrical solenoids and with a homogeneous magnetic field in
their interior. First, in the Sobolev space , we characterize all
generalized boundary conditions on the solenoid bor- der compatible with
quantum mechanics, i.e., the boundary conditions so that the corresponding
hamiltonian operators are self-adjoint. Then we study and compare the
scattering of the most usual boundary con- ditions, that is, Dirichlet, Neumann
and Robin.Comment: 40 pages, 5 figure
Desempenho produtivo de populações segregantes de copas de pereira (Pyrus spp.) nas safras 2012-13 e 2013-14.
O objetivo do trabalho foi avaliar a fenologia e a produção de híbridos de copas, obtidos pelo programa de melhoramento genético de pereira da Embrapa Uva e Vinho, estabelecidos na Estação Experimental de Fruticultura de Clima Temperado, em Vacaria, RS
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