11,808 research outputs found
Adiabatic quantum search with atoms in a cavity driven by lasers
We propose an implementation of the quantum search algorithm of a marked item
in an unsorted list of N items by adiabatic passage in a cavity-laser-atom
system. We use an ensemble of N identical three-level atoms trapped in a
single-mode cavity and driven by two lasers. In each atom, the same level
represents a database entry. One of the atoms is marked by having an energy gap
between its two ground states. Appropriate time delays between the two laser
pulses allow one to populate the marked state starting from an initial
entangled state within a decoherence-free adiabatic subspace. The time to
achieve such a process is shown to exhibit the Grover speedup.Comment: 5 pages, 3 figure
Quantitative estimates for the long time behavior of an ergodic variant of the telegraph process
Motivated by stability questions on piecewise deterministic Markov models of
bacterial chemotaxis, we study the long time behavior of a variant of the
classic telegraph process having a non-constant jump rate that induces a drift
towards the origin. We compute its invariant law and show exponential
ergodicity, obtaining a quantitative control of the total variation distance to
equilibrium at each instant of time. These results rely on an exact description
of the excursions of the process away from the origin and on the explicit
construction of an original coalescent coupling for both velocity and position.
Sharpness of the obtained convergence rate is discussed.Comment: Definitive version of former paper "Quantitative estimates for the
long time behavior of a PDMP describing the movement of bacteria", now
accepted in Advances in Applied Probability. Presentation changed. A
diffusive scaling limit result is added. Sharpness of the long-time
convergence rate is discussed. 20 pages, 3 figure
A robust extension to the triple plane pressure mode matching method by filtering convective perturbations
Time-periodic CFD simulations are widely used to investigate turbomachinery
components. The triple-plane pressure mode matching method (TPP) developed by
Ovenden and Rienstra extracts the acoustic part in such simulations. Experience
shows that this method is subject to significant errors when the amplitude of
pseudo-sound is high compared to sound. Pseudo-sound are unsteady pressure
fluctuations with a convective character. The presented extension to the TPP
improves the splitting between acoustics and the rest of the unsteady flow
field. The method is simple: i) the acoustic eigenmodes are analytically
determined for a uniform mean flow as in the original TPP; ii) the suggested
model for convective pressure perturbations uses the convective wavenumber as
axial wavenumber and the same orthogonal radial shape functions as for the
acoustic modes. The reliability is demonstrated on the simulation data of a
low-pressure fan. As acoustic and convective perturbations are separated, the
accuracy of the results increases close to sources, allowing a reduction of the
computational costs by shortening the simulation domain. The extended method is
as robust as the original one--giving the same results for the acoustic modes
in absence of convective perturbations.Comment: Accepted 15-05-11 by International Journal of Aeroacoustics to be
published in the special issue focusing on turbomachinery aeroacoustic
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