440 research outputs found
Deterministic cavity quantum electrodynamics with trapped ions
We have employed radio-frequency trapping to localize a single 40Ca+-ion in a high-finesse optical cavity. By means of laser Doppler cooling, the position spread of the ion's wavefunction along the cavity axis was reduced to 42 nm, a fraction of the resonance wavelength of ionized calcium (λ = 397 nm). By controlling the position of the ion in the optical field, continuous and completely deterministic coupling of ion and field was realized. The precise three-dimensional location of the ion in the cavity was measured by observing the fluorescent light emitted upon excitation in the cavity field. The single-ion system is ideally suited to implement cavity quantum electrodynamics under cw conditions. To this end we operate the cavity on the D3/2âP1/2 transition of 40Ca+ (λ = 866 nm). Applications include the controlled generation of single-photon pulses with high efficiency and two-ion quantum gates
Inflation and initial conditions in the pre-big bang scenario
The pre-big bang scenario describes the evolution of the Universe from an
initial state approaching the flat, cold, empty, string perturbative vacuum.
The choice of such an initial state is suggested by the present state of our
Universe if we accept that the cosmological evolution is (at least partially)
duality-symmetric. Recently, the initial conditions of the pre-big bang
scenario have been criticized as they introduce large dimensionless parameters
allowing the Universe to be "exponentially large from the very beginning". We
agree that a set of initial parameters (such as the initial homogeneity scale,
the initial entropy) larger than those determined by the initial horizon scale,
H^{-1}, would be somewhat unnatural to start with. However, in the pre-big bang
scenario, the initial parameters are all bounded by the size of the initial
horizon. The basic question thus becomes: is a maximal homogeneity scale of
order H^{-1} necessarily unnatural if the initial curvature is small and,
consequently, H^{-1} is very large in Planck (or string) units? In the
impossibility of experimental information one could exclude "a priori", for
large horizons, the maximal homogeneity scale H^{-1} as a natural initial
condition. In the pre-big bang scenario, however, pre-Planckian initial
conditions are not necessarily washed out by inflation and are accessible (in
principle) to observational tests, so that their naturalness could be also
analyzed with a Bayesan approach, in terms of "a posteriori" probabilities.Comment: 4 pages, Latex, one figure. Many references added. The text has been
improved in many points. To appear in Phys. Rev.
The Sasa-Satsuma higher order nonlinear Schrodinger equation and its bilinearization and multi-soliton solutions
Higher order and multicomponent generalizations of the nonlinear Schrodinger
equation are important in various applications, e.g., in optics. One of these
equations, the integrable Sasa-Satsuma equation, has particularly interesting
soliton solutions. Unfortunately the construction of multi-soliton solutions to
this equation presents difficulties due to its complicated bilinearization. We
discuss briefly some previous attempts and then give the correct
bilinearization based on the interpretation of the Sasa-Satsuma equation as a
reduction of the three-component Kadomtsev-Petvishvili hierarchy. In the
process we also get bilinearizations and multi-soliton formulae for a two
component generalization of the Sasa-Satsuma equation (the
Yajima-Oikawa-Tasgal-Potasek model), and for a (2+1)-dimensional
generalization.Comment: 13 pages in RevTex, added reference
Estimating Small Area Income Deprivation: An Iterative Proportional Fitting Approach
Small area estimation and in particular the estimation of small area income deprivation has
potential value in the development of new or alternative components of multiple deprivation
indices. These new approaches enable the development of income distribution threshold based
as opposed to benefit count based measures of income deprivation and so enable the
alignment of regional and national measures such as the Households Below Average Income
with small area measures. This paper briefly reviews a number of approaches to small area
estimation before describing in some detail an iterative proportional fitting based spatial
microsimulation approach. This approach is then applied to the estimation of small area HBAI
rates at the small area level in Wales in 2003-5. The paper discusses the results of this
approach, contrasts them with contemporary âofficialâ income deprivation measures for the
same areas and describes a range of ways to assess the robustness of the results
Gravitational collapse with tachyon field and barotropic fluid
A particular class of space-time, with a tachyon field, \phi, and a
barotropic fluid constituting the matter content, is considered herein as a
model for gravitational collapse. For simplicity, the tachyon potential is
assumed to be of inverse square form i.e., V(\phi) \sim \phi^{-2}. Our purpose,
by making use of the specific kinematical features of the tachyon, which are
rather different from a standard scalar field, is to establish the several
types of asymptotic behavior that our matter content induces. Employing a
dynamical system analysis, complemented by a thorough numerical study, we find
classical solutions corresponding to a naked singularity or a black hole
formation. In particular, there is a subset where the fluid and tachyon
participate in an interesting tracking behaviour, depending sensitively on the
initial conditions for the energy densities of the tachyon field and barotropic
fluid. Two other classes of solutions are present, corresponding respectively,
to either a tachyon or a barotropic fluid regime. Which of these emerges as
dominant, will depend on the choice of the barotropic parameter, \gamma.
Furthermore, these collapsing scenarios both have as final state the formation
of a black hole.Comment: 18 pages, 7 figures. v3: minor changes. Final version to appear in
GR
Spin correlated interferometry for polarized and unpolarized photons on a beam splitter
Spin interferometry of the 4th order for independent polarized as well as
unpolarized photons arriving simultaneously at a beam splitter and exhibiting
spin correlation while leaving it, is formulated and discussed in the quantum
approach. Beam splitter is recognized as a source of genuine singlet photon
states. Also, typical nonclassical beating between photons taking part in the
interference of the 4th order is given a polarization dependent explanation.Comment: RevTeX, 19 pages, 1 ps figure, author web page at
http://m3k.grad.hr/pavici
Collective oscillations of a 1D trapped Bose gas
Starting from the hydrodynamic equations of superfluids, we calculate the
frequencies of the collective oscillations of a harmonically trapped Bose gas
for various 1D configurations. These include the mean field regime described by
Gross-Pitaevskii theory and the beyond mean field regime at small densities
described by Lieb-Liniger theory. The relevant combinations of the physical
parameters governing the transition between the different regimes are
discussed.Comment: 4 pages, 2 figure
Photoionisation loading of large Sr+ ion clouds with ultrafast pulses
This paper reports on photoionisation loading based on ultrafast pulses of
singly-ionised strontium ions in a linear Paul trap. We take advantage of an
autoionising resonance of Sr neutral atoms to form Sr+ by two-photon absorption
of femtosecond pulses at a wavelength of 431nm. We compare this technique to
electron-bombardment ionisation and observe several advantages of
photoionisation. It actually allows the loading of a pure Sr+ ion cloud in a
low radio-frequency voltage amplitude regime. In these conditions up to 4x10^4
laser-cooled Sr+ ions were trapped
Dilatonic Black Holes in Higher Curvature String Gravity
We give analytical arguments and demonstrate numerically the existence of
black hole solutions of the Effective Superstring Action in the presence
of Gauss-Bonnet quadratic curvature terms. The solutions possess non-trivial
dilaton hair. The hair, however, is of ``secondary" type", in the sense that
the dilaton charge is expressed in terms of the black hole mass. Our solutions
are not covered by the assumptions of existing proofs of the ``no-hair"
theorem. We also find some alternative solutions with singular metric
behaviour, but finite energy. The absence of naked singularities in this system
is pointed out.Comment: 22 pages, Latex file, 7 Latex figures already include
Sensitivity of a tonne-scale NEXT detector for neutrinoless double beta decay searches
The Neutrino Experiment with a Xenon TPC (NEXT) searches for the neutrinoless
double-beta decay of Xe-136 using high-pressure xenon gas TPCs with
electroluminescent amplification. A scaled-up version of this technology with
about 1 tonne of enriched xenon could reach in less than 5 years of operation a
sensitivity to the half-life of neutrinoless double-beta decay decay better
than 1E27 years, improving the current limits by at least one order of
magnitude. This prediction is based on a well-understood background model
dominated by radiogenic sources. The detector concept presented here represents
a first step on a compelling path towards sensitivity to the parameter space
defined by the inverted ordering of neutrino masses, and beyond.Comment: 22 pages, 11 figure
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