4,344 research outputs found
Availability and mean time between failures of redundant systems with random maintenance of subsystems
It is shown how the availability and MTBF (Mean Time Between Failures) of a redundant system with subsystems maintenanced at the points of so-called stationary renewal processes can be determined from the distributions of the intervals between maintenance actions and of the failure-free operating intervals of the subsystems. The results make it possible, for example, to determine the frequency and duration of hidden failure states in computers which are incidentally corrected during the repair of observed failures
Panel Regression with Random Noise
The paper explores the effect of measurement errors on the estimation of a linear panel data model. The conventional fixed effects estimator, which ignores measurement errors, is biased. By correcting for the bias one can construct consistent and asymptotically normal estimators. In addition, we find estimates for the asymptotic variances of these estimators. The paper focuses on multiplicative errors, which are often deliberately added to the data in order to minimize their disclosure risk. They can be analyzed in a similar way as additive errors, but with some important and consequential differences.panel regression, multiplicative measurement errors, bias correction, asymptotic variance, disclosure control
Dynamical polarizability of atoms in arbitrary light fields: general theory and application to cesium
We present a systematic derivation of the dynamical polarizability and the ac
Stark shift of the ground and excited states of atoms interacting with a
far-off-resonance light field of arbitrary polarization. We calculate the
scalar, vector, and tensor polarizabilities of atomic cesium using resonance
wavelengths and reduced matrix elements for a large number of transitions. We
analyze the properties of the fictitious magnetic field produced by the vector
polarizability in conjunction with the ellipticity of the polarization of the
light field.Comment: see also Supplemental Materia
Near-ground-state cooling of atoms optically trapped 300nm away from a hot surface
Laser-cooled atoms coupled to nanophotonic structures constitute a powerful
research platform for the exploration of new regimes of light-matter
interaction. While the initialization of the atomic internal degrees of freedom
in these systems has been achieved, a full preparation of the atomic quantum
state also requires controlling the center of mass motion of the atoms at the
quantum level. Obtaining such control is not straightforward, due to the close
vicinity of the atoms to the photonic system that is at ambient temperature.
Here, we demonstrate cooling of individual neutral Cesium atoms, that are
optically interfaced with light in an optical nanofiber, preparing them close
to their three-dimensional motional ground state. The atoms are localized less
than 300nm away from the hot fiber surface. Ground-state preparation is
achieved by performing degenerate Raman cooling, and the atomic temperature is
inferred from the analysis of heterodyne fluorescence spectroscopy signals. Our
cooling method can be implemented either with externally applied or guided
light fields. Moreover, it relies on polarization gradients which naturally
occur for strongly confined guided optical fields. Thus, this method can be
implemented in any trap based on nanophotonic structures. Our results provide
an ideal starting point for the study of novel effects such as light-induced
self-organization, the measurement of novel optical forces, and the
investigation of heat transfer at the nanoscale using quantum probes
Heating in Nanophotonic Traps for Cold Atoms
Laser-cooled atoms that are trapped and optically interfaced with light in
nanophotonic waveguides are a powerful platform for fundamental research in
quantum optics as well as for applications in quantum communication and quantum
information processing. Ever since the first realization of such a hybrid
quantum nanophotonic, heating rates of the atomic motion observed in various
experimental settings have typically been exceeding those in comparable
free-space optical microtraps by about three orders of magnitude. This
excessive heating is a roadblock for the implementation of certain protocols
and devices. Its origin has so far remained elusive and, at the typical
atom-surface separations of less than an optical wavelength encountered in
nanophotonic traps, numerous effects may potentially contribute to atom
heating. Here, we theoretically describe the effect of mechanical vibrations of
waveguides on guided light fields and provide a general theory of
particle-phonon interaction in nanophotonic traps. We test our theory by
applying it to the case of laser-cooled cesium atoms in nanofiber-based
two-color optical traps. We find excellent quantitative agreement between the
predicted heating rates and experimentally measured values. Our theory predicts
that, in this setting, the dominant heating process stems from the
optomechanical coupling of the optically trapped atoms to the continuum of
thermally occupied flexural mechanical modes of the waveguide structure. Beyond
unraveling the long-standing riddle of excessive heating in nanofiber-based
atom traps, we also study the dependence of the heating rates on the relevant
system parameters. Our findings allow us to propose several strategies for
minimizing the heating. Finally, our findings are also highly relevant for
optomechanics experiments with dielectric nanoparticles that are optically
trapped close to nanophotonic waveguides.Comment: Published version. 35 pages (including appendices), 7 figures, 18
tables, and 3 pages of supplemental materia
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