633 research outputs found
Understanding the production of dual BEC with sympathetic cooling
We show, both experimentally and theoretically, that sympathetic cooling of
Rb atoms in the state by evaporatively cooled atoms in the
state can be precisely controlled to produce dual or single
condensate in either state. We also study the thermalization rate between two
species. Our model renders a quantitative account of the observed role of the
overlap between the two clouds and points out that sympathetic cooling becomes
inefficient when the masses are very different. Our calculation also yields an
analytical expression of the thermalization rate for a single species.Comment: 3 figure
Entanglement and squeezing in a two-mode system: theory and experiment
We report on the generation of non separable beams produced via the
interaction of a linearly polarized beam with a cloud of cold cesium atoms
placed in an optical cavity. We convert the squeezing of the two linear
polarization modes into quadrature entanglement and show how to find out the
best entanglement generated in a two-mode system using the inseparability
criterion for continuous variable [Duan et al., Phys. Rev. Lett. 84, 2722
(2000)]. We verify this method experimentally with a direct measurement of the
inseparability using two homodyne detections. We then map this entanglement
into a polarization basis and achieve polarization entanglement.Comment: submitted to J. Opt. B for a Special Issue on Foundations of Quantum
Optic
Study of flavour dependencies in leptogenesis
We study the impact of flavours on the efficiency factors and give analytical
and numerical results of the baryon asymmetry taking into account the different
charged lepton Yukawa contributions and the complete (diagonal and
off-diagonal) to conversion matrix. With this treatment we update
the lower bound on the lightest right-handed neutrino mass.Comment: 13 pages, 11 figures. typos corrected, some formulae modified. 2
figures and discussion adde
Flavour Issues in Leptogenesis
We study the impact of flavour in thermal leptogenesis, including the quantum
oscillations of the asymmetries in lepton flavour space. In the Boltzmann
equations we find different numerical factors and additional terms which can
affect the results significantly. The upper bound on the CP asymmetry in a
specific flavour is weaker than the bound on the sum. This suggests that --
when flavour dynamics is included -- there is no model-independent limit on the
light neutrino mass scale,and that the lower bound on the reheat temperature is
relaxed by a factor ~ (3 - 10).Comment: 19 pages, corrected equations for flavour oscillation
CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis
We obtain the Boltzmann equations for leptogenesis including decay and
scattering processes with two and three body initial or final states. We
present an explicit computation of the CP violating scattering asymmetries. We
analyze their possible impact in leptogenesis, and we discuss the validity of
their approximate expressions in terms of the decay asymmetry. In scenarios in
which the initial heavy neutrino density vanishes, the inclusion of CP
asymmetries in scatterings can enforce a cancellation between the lepton
asymmetry generated at early times and the asymmetry produced at later times.
We argue that a sizeable amount of washout is crucial for spoiling this
cancellation, and we show that in the regimes in which the washouts are
particularly weak, the inclusion of CP violation in scatterings yields a
reduction in the final value of the lepton asymmetry. In the strong washout
regimes the inclusion of CP violation in scatterings still leads to a
significant enhancement of the lepton asymmetry at high temperatures; however,
due to the independence from the early conditions that is characteristic of
these regimes, the final value of the lepton asymmetry remains approximately
unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and
corresponding figures (mainly fig. 3) corrected. Final version to be
published in JHE
Many-body quantum dynamics of polarisation squeezing in optical fibre
We report new experiments that test quantum dynamical predictions of
polarization squeezing for ultrashort photonic pulses in a birefringent fibre,
including all relevant dissipative effects. This exponentially complex
many-body problem is solved by means of a stochastic phase-space method. The
squeezing is calculated and compared to experimental data, resulting in
excellent quantitative agreement. From the simulations, we identify the
physical limits to quantum noise reduction in optical fibres. The research
represents a significant experimental test of first-principles time-domain
quantum dynamics in a one-dimensional interacting Bose gas coupled to
dissipative reservoirs.Comment: 4 pages, 4 figure
Quantum polarization tomography of bright squeezed light
We reconstruct the polarization sector of a bright polarization squeezed beam
starting from a complete set of Stokes measurements. Given the symmetry that
underlies the polarization structure of quantum fields, we use the unique SU(2)
Wigner distribution to represent states. In the limit of localized and bright
states, the Wigner function can be approximated by an inverse three-dimensional
Radon transform. We compare this direct reconstruction with the results of a
maximum likelihood estimation, finding an excellent agreement.Comment: 15 pages, 5 figures. Contribution to New Journal of Physics, Focus
Issue on Quantum Tomography. Comments welcom
Simulations and Experiments on Polarisation Squeezing in Optical Fibre
We investigate polarisation squeezing of ultrashort pulses in optical fibre,
over a wide range of input energies and fibre lengths. Comparisons are made
between experimental data and quantum dynamical simulations, to find good
quantitative agreement. The numerical calculations, performed using both
truncated Wigner and exact phase-space methods, include nonlinear and
stochastic Raman effects, through coupling to phonons variables. The
simulations reveal that excess phase noise, such as from depolarising GAWBS,
affects squeezing at low input energies, while Raman effects cause a marked
deterioration of squeezing at higher energies and longer fibre lengths. The
optimum fibre length for maximum squeezing is also calculated.Comment: 19 pages, lots of figure
Hybrid in vitro diffusion cell for simultaneous evaluation of hair and skin decontamination: temporal distribution of chemical contaminants
Most casualty or personnel decontamination studies have focused on removing contaminants from the skin. However, scalp hair and underlying skin are the most likely areas of contamination following airborne exposure to chemicals. The aim of this study was to investigate the interactions of contaminants with scalp hair and underlying skin using a hybrid in vitro diffusion cell model. The in vitro hybrid test system comprised âcurtainsâ of human hair mounted onto sections of excised porcine skin within a modified diffusion cell. The results demonstrated that hair substantially reduced underlying scalp skin contamination and that hair may provide a limited decontamination effect by removing contaminants from the skin surface. This hybrid test system may have application in the development of improved chemical incident response processes through the evaluation of various hair and skin decontamination strategies.Peer reviewedFinal Published versio
Offshore monopile in the southern North Sea: Part I, calibrated input sea state
Safe, reliable access is an essential precondition for the successful maintenance of offshore wind farms. Access from vessels to wind turbines depends on the severity of the sea state in the vicinity of the turbine support structure. This paper presents a validation of a numerical boundary condition developed to reproduce the seasonal sea state at Teesside Offshore Wind Farm, off the coast of the UK. The boundary condition, called customSpectrum, was derived from wave energy spectra obtained by analysis of existing field measurements of wave free-surface displacement at the wind farm site and implemented in OpenFoam, the open-source computational fluid dynamics library. OpenFoam was then used to simulate typical spring, summer, autumn and winter sea states as uni-directional waves. Predicted surface elevations and significant wave heights were found to be in agreement with in situ buoy data, thus validating the OpenFoam model. Satisfactory agreement was achieved between analytical and numerically predicted spectral density functions for the horizontal and vertical water particle velocity components. It was found that the wave activity at Teesside is uni-modal in spring and autumn, and bi-modal in summer and winter. Extending the procedure to multi-directional waves in crossing seas is recommended
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