126 research outputs found
Continuum damage mechanics model as an instrument for development of design rules for steel structures in seismic affected zones
Trapping of Single Atoms with Single Photons in Cavity QED
Two recent experiments have reported the trapping of individual atoms inside
optical resonators by the mechanical forces associated with single photons
[Hood et al., Science 287, 1447 (2000) and Pinkse et al., Nature 404, 365
(2000)]. Here we analyze the trapping dynamics in these settings, focusing on
two points of interest. Firstly, we investigate the extent to which
light-induced forces in these experiments are distinct from their free-space
counterparts. Secondly, we explore the quantitative features of the resulting
atomic motion and how these dynamics are mapped onto variations of the
intracavity field. Not surprisingly, qualitatively distinct atomic dynamics
arise as the coupling and dissipative rates are varied. For the experiment of
Hood et al., we show that atomic motion is largely conservative and is
predominantly in radial orbits transverse to the cavity axis. A comparison with
the free-space theory demonstrates that the fluctuations of the dipole force
are suppressed by an order of magnitude. This effect is based upon the
Jaynes-Cummings eigenstates of the atom-cavity system and represents
qualitatively new physics for optical forces at the single-photon level. By
contrast, even in a regime of strong coupling in the experiment of Pinkse et
al., there are only small quantitative distinctions between the free-space
theory and the quantum theory, so it is not clear that description of this
experiment as a novel single-quantum trapping effect is necessary. The atomic
motion is strongly diffusive, leading to an average localization time
comparable to the time for an atom to transit freely through the cavity and to
a reduction in the ability to infer aspects of the atomic motion from the
intracavity photon number.Comment: 19 pages, 22 figure files, REVTEX, corrected spelling, LaTeX now
produces postscript which includes figures, minor changes to figures. Final
version to be published in Physical Review A, expanded summary of results in
introduction, minor changes to figures and tex
Coherent dynamics of Bose-Einstein condensates in high-finesse optical cavities
We study the mutual interaction of a Bose-Einstein condensed gas with a
single mode of a high-finesse optical cavity. We show how the cavity
transmission reflects condensate properties and calculate the self-consistent
intra-cavity light field and condensate evolution. Solving the coupled
condensate-cavity equations we find that while falling through the cavity, the
condensate is adiabatically transfered into the ground state of the periodic
optical potential. This allows time dependent non-destructive measurements on
Bose-Einstein condensates with intriguing prospects for subsequent controlled
manipulation.Comment: 5 pages, 5 figures; revised version: added reference
Micromechanical fatigue experiments for validation of microstructure-sensitive fatigue simulation models
Crack initiation governs high cycle fatigue life and is sensitive to microstructural details. While corresponding microstructure-sensitive models are available, their validation is difficult. We propose a validation framework where a fatigue test is mimicked in a sub-modeling simulation by embedding the measured microstructure into the specimen geometry and adopting an approximation of the experimental boundary conditions. Exemplary, a phenomenological crystal plasticity model was applied to predict deformation in ferritic steel (EN1.4003). Hotspots in commonly used fatigue indicator parameter maps are compared with damage segmented from micrographs. Along with the data, the framework is published for benchmarking future micromechanical fatigue models
Micromechanical fatigue experiments for validation of microstructure-sensitive fatigue simulation models
Crack initiation governs high cycle fatigue life and is sensitive to microstructural details. While corresponding microstructure-sensitive models are available, their validation is difficult. We propose a validation framework where a fatigue test is mimicked in a sub-modeling simulation by embedding the measured microstructure into the specimen geometry and adopting an approximation of the experimental boundary conditions. Exemplary, a phenomenological crystal plasticity model was applied to predict deformation in ferritic steel (EN1.4003). Hotspots in commonly used fatigue indicator parameter maps are compared with damage segmented from micrographs. Along with the data, the framework is published for benchmarking future micromechanical fatigue models
Scaling properties of cavity-enhanced atom cooling
We extend an earlier semiclassical model to describe the dissipative motion
of N atoms coupled to M modes inside a coherently driven high-finesse cavity.
The description includes momentum diffusion via spontaneous emission and cavity
decay. Simple analytical formulas for the steady-state temperature and the
cooling time for a single atom are derived and show surprisingly good agreement
with direct stochastic simulations of the semiclassical equations for N atoms
with properly scaled parameters. A thorough comparison with standard free-space
Doppler cooling is performed and yields a lower temperature and a cooling time
enhancement by a factor of M times the square of the ratio of the atom-field
coupling constant to the cavity decay rate. Finally it is shown that laser
cooling with negligible spontaneous emission should indeed be possible,
especially for relatively light particles in a strongly coupled field
configuration.Comment: 7 pages, 5 figure
Commentary and Worked Examples to EN 1993-1-10 "Material Toughness and Through Thickness Properties" and Other Toughness Oriented Rules in EN 1993
This commentary gives explanations and worked examples to the design rules in Eurocode 3 that are influenced by the strength and toughness properties of the structural steels used. It is a commentary and background document to EN 1993-1-10 "Material toughness and through thickness properties" and its extension in EN 1993-1-12 "Design rules for high-strength steels", where toughness properties are explicitly addressed.
It however provides also background to other parts of EN 1993, e.g. to EN 1993-1-1 "Design of steel structures - Basic rules and rules for buildings", where the design rules are related only to strength properties as the yield strength and the tensile strength without explicitly mentioning the role of toughness that is hidden behind the resistance formulae. Finally it gives some comments to chapter 6 of EN 1998-1: "Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings".JRC.G.5-European laboratory for structural assessmen
Fast cavity-enhanced atom detection with low noise and high fidelity
Cavity quantum electrodynamics describes the fundamental interactions between
light and matter, and how they can be controlled by shaping the local
environment. For example, optical microcavities allow high-efficiency detection
and manipulation of single atoms. In this regime fluctuations of atom number
are on the order of the mean number, which can lead to signal fluctuations in
excess of the noise on the incident probe field. Conversely, we demonstrate
that nonlinearities and multi-atom statistics can together serve to suppress
the effects of atomic fluctuations when making local density measurements on
clouds of cold atoms. We measure atom densities below 1 per cavity mode volume
near the photon shot-noise limit. This is in direct contrast to previous
experiments where fluctuations in atom number contribute significantly to the
noise. Atom detection is shown to be fast and efficient, reaching fidelities in
excess of 97% after 10 us and 99.9% after 30 us.Comment: 7 pages, 4 figures, 1 table; extensive changes to format and
discussion according to referee comments; published in Nature Communications
with open acces
Trapping atoms in the vacuum field of a cavity
The aim of this work is to find ways to trap an atom in a cavity. In contrast
to other approaches we propose a method where the cavity is basically in the
vacuum state and the atom in the ground state. The idea is to induce a spatial
dependent AC Stark shift by irradiating the atom with a weak laser field, so
that the atom experiences a trapping force. The main feature of our setup is
that dissipation can be strongly suppressed. We estimate the lifetime of the
atom as well as the trapping potential parameters and compare our estimations
with numerical simulations.Comment: 8 pages, 8 figure
A position-momentum EPR state of distantly-separated trapped atoms
We propose a scheme for preparing an EPR state in position and momentum of a
pair of distantly-separated trapped atoms. The scheme utilizes the entangled
light fields output from a nondegenerate optical parametric amplifier. Quantum
state exchange between these fields and the motional states of the trapped
atoms is accomplished via interactions in cavity QED.Comment: 5 pages, 2 figures, submitted to Phys. Rev.
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