58,038 research outputs found

    Optimized Double-well quantum interferometry with Gaussian squeezed-states

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    A Mach-Zender interferometer with a gaussian number-difference squeezed input state can exhibit sub-shot-noise phase resolution over a large phase-interval. We obtain the optimal level of squeezing for a given phase-interval Δθ0\Delta\theta_0 and particle number NN, with the resulting phase-estimation uncertainty smoothly approaching 3.5/N3.5/N as Δθ0\Delta\theta_0 approaches 10/N, achieved with highly squeezed states near the Fock regime. We then analyze an adaptive measurement scheme which allows any phase on (π/2,π/2)(-\pi/2,\pi/2) to be measured with a precision of 3.5/N3.5/N requiring only a few measurements, even for very large NN. We obtain an asymptotic scaling law of Δθ(2.1+3.2ln(ln(NtottanΔθ0)))/Ntot\Delta\theta\approx (2.1+3.2\ln(\ln(N_{tot}\tan\Delta\theta_0)))/N_{tot}, resulting in a final precision of 10/Ntot\approx 10/N_{tot}. This scheme can be readily implemented in a double-well Bose-Einstein condensate system, as the optimal input states can be obtained by adiabatic manipulation of the double-well ground state.Comment: updated versio

    The density of organized vortices in a turbulent mixing layer

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    It is argued on the basis of exact solutions for uniform vortices in straining fields that vortices of finite cross-section in a row will disintegrate if the spacing is too small. The results are applied to the organized vortex structures observed in turbulent mixing layers. An explanation is provided for the disappearance of these structures as they move downstream and it is deduced that the ratio of average spacing to width should be about 3·5, the width being defined by the maximum slope of the mean velocity. It is shown in an appendix that walls have negligible effect

    The rise of a body through a rotating fluid in a container of finite length

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    The drag on an axisymmetric body rising through a rotating fluid of small viscosity rotating about a vertical axis is calculated on the assumption that there is a Taylor column ahead of and behind the body, in which the geostrophic flow is determined by compatibility conditions on the Ekman boundary-layers on the body and the end surfaces. It is assumed that inertia effects may be neglected. Estimates are given of the conditions for which the theory should be valid

    Classical Sphaleron Rate on Fine Lattices

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    We measure the sphaleron rate for hot, classical Yang-Mills theory on the lattice, in order to study its dependence on lattice spacing. By using a topological definition of Chern-Simons number and going to extremely fine lattices (up to beta=32, or lattice spacing a = 1 / (8 g^2 T)) we demonstrate nontrivial scaling. The topological susceptibility, converted to physical units, falls with lattice spacing on fine lattices in a way which is consistent with linear dependence on aa (the Arnold-Son-Yaffe scaling relation) and strongly disfavors a nonzero continuum limit. We also explain some unusual behavior of the rate in small volumes, reported by Ambjorn and Krasnitz.Comment: 14 pages, includes 5 figure

    Landau-Pomeranchuk-Migdal resummation for dilepton production

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    We consider the thermal emission rate of dileptons from a QCD plasma in the small invariant mass (Q^2 \sim \gs^2 T^2) but large energy (q^0 \gsim T) range. We derive an integral equation which resums multiple scatterings to include the LPM effect; it is valid at leading order in the coupling. Then we recast it as a differential equation and show a simple algorithm for its solution. We present results for dilepton rates at phenomenologically interesting energies and invariant masses.Comment: 19 pages, 7 postscript figures, test program available at http://www-spht.cea.fr/articles/T02/150/libLPM
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