423 research outputs found
Simulation in Quality Management – An Approach to Improve Inspection Planning
Production is a multi-step process involving many different articles produced in different jobs by various machining stations. Quality inspection has to be integrated in the production sequence in order to ensure the conformance of the products. The interactions between manufacturing processes and inspections are very complex since three aspects (quality, cost, and time) should all be considered at the same time while determining the suitable inspection strategy. Therefore, a simulation approach was introduced to solve this problem.The simulator called QUINTE [the QUINTE simulator has been developed at the University of Dortmund in the course of two research projects funded by the German Federal Ministry of Economics and Labour (BMWA: Bundesministerium fĂĽr Wirtschaft und Arbeit), the Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF), Cologne/Germany and the Forschungsgemeinschaft Qualität, Frankfurt a.M./Germany] was developed to simulate the machining as well as the inspection. It can be used to investigate and evaluate the inspection strategies in manufacturing processes. The investigation into the application of QUINTE simulator in industry was carried out at two pilot companies. The results show the validity of this simulator. An attempt to run QUINTE in a user-friendly environment, i.e., the commercial simulation software – Arena® is also described in this paper.NOTATION: QUINTE Qualität in der Teilefertigung (Quality in the manufacturing process)Â
Signatures of a Bardeen-Cooper-Schrieffer Polariton Laser
Microcavity exciton polariton systems can have a wide range of macroscopic
quantum effects that may be turned into better photonic technologies. Polariton
Bose-Einstein condensation (BEC) and photon lasing have been widely accepted in
the limits of low and high carrier densities, but identification of the
expected Bardeen-Cooper-Schrieffer (BCS) state at intermediate densities
remains elusive. While all three phases feature coherent photon emission,
essential differences exist in their matter media. Most studies to date
characterize only the photon field. Here, using a microcavity with strong- and
weak-couplings co-existing in orthogonal linear polarizations, we directly
measure the electronic gain in the matter media of a polariton laser,
demonstrating a BCS-like polariton laser above the Mott transition density.
Theoretical analysis reproduces the absorption spectra and lasing frequency
shifts, revealing an electron distribution function characteristic of a
polariton BCS state but modified by incoherent pumping and dissipation
Intensity fluctuations in bimodal micropillar lasers enhanced by quantum-dot gain competition
We investigate correlations between orthogonally polarized cavity modes of a
bimodal micropillar laser with a single layer of self-assembled quantum dots in
the active region. While one emission mode of the microlaser demonstrates a
characteristic s-shaped input-output curve, the output intensity of the second
mode saturates and even decreases with increasing injection current above
threshold. Measuring the photon auto-correlation function g^{(2)}(\tau) of the
light emission confirms the onset of lasing in the first mode with g^{(2)}(0)
approaching unity above threshold. In contrast, strong photon bunching
associated with super-thermal values of g^{(2)}(0) is detected for the other
mode for currents above threshold. This behavior is attributed to gain
competition of the two modes induced by the common gain material, which is
confirmed by photon crosscorrelation measurements revealing a clear
anti-correlation between emission events of the two modes. The experimental
studies are in excellent qualitative agreement with theoretical studies based
on a microscopic semiconductor theory, which we extend to the case of two modes
interacting with the common gain medium. Moreover, we treat the problem by an
extended birth-death model for two interacting modes, which reveals, that the
photon probability distribution of each mode has a double peak structure,
indicating switching behavior of the modes for the pump rates around threshold.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Critical dynamics of ballistic and Brownian particles in a heterogeneous environment
The dynamic properties of a classical tracer particle in a random, disordered
medium are investigated close to the localization transition. For Lorentz
models obeying Newtonian and diffusive motion at the microscale, we have
performed large-scale computer simulations, demonstrating that universality
holds at long times in the immediate vicinity of the transition. The scaling
function describing the crossover from anomalous transport to diffusive motion
is found to vary extremely slowly and spans at least 5 decades in time. To
extract the scaling function, one has to allow for the leading universal
corrections to scaling. Our findings suggest that apparent power laws with
varying exponents generically occur and dominate experimentally accessible time
windows as soon as the heterogeneities cover a decade in length scale. We
extract the divergent length scales, quantify the spatial heterogeneities in
terms of the non-Gaussian parameter, and corroborate our results by a thorough
finite-size analysis.Comment: 14 page
Carrier trapping and luminescence polarization in quantum dashes
We study experimentally and theoretically polarization-dependent luminescence
from an ensemble of quantum-dot-like nanostructures with a very large in-plane
shape anisotropy (quantum dashes). We show that the measured degree of linear
polarization of the emitted light increases with the excitation power and
changes with temperature in a non-trivial way, depending on the excitation
conditions. Using an approximate model based on the k.p theory, we are able to
relate this degree of polarization to the amount of light hole admixture in the
exciton states which, in turn, depends on the symmetry of the envelope wave
function. Agreement between the measured properties and theory is reached under
assumption that the ground exciton state in a quantum dash is trapped in a
confinement fluctuation within the structure and thus localized in a much
smaller volume of much lower asymmetry than the entire nanostructure.Comment: 13 pages, 9 figures; considerably extended, additional discussion and
new figures include
Nonlinear photoluminescence spectra from a quantum dot-cavity system: Direct evidence of pump-induced stimulated emission and anharmonic cavity-QED
We investigate the power-dependent photoluminescence spectra from a strongly
coupled quantum dot-cavity system using a quantum master equation technique
that accounts for incoherent pumping, pure dephasing, and fermion or boson
statistics. Analytical spectra at the one-photon correlation level and the
numerically exact multi-photon spectra for fermions are presented. We compare
to recent experiments on a quantum dot-micropiller cavity system and show that
an excellent fit to the data can be obtained by varying only the incoherent
pump rates in direct correspondence with the experiments. Our theory and
experiments together show a clear and systematic way of studying
stimulated-emission induced broadening and anharmonic cavity-QED.Comment: We have reworked our previous arXiv paper and submitted this latest
version for peer revie
Quantum-dot single-photon sources for entanglement enhanced interferometry
The authors acknowledge financial support from the Center for Integrated Quantum Science and Technology (IQST).Multiphoton entangled states such as “N00N states” have attracted a lot of attention because of their possible application in high-precision, quantum enhanced phase determination. So far, N00N states have been generated in spontaneous parametric down-conversion processes and by mixing quantum and classical light on a beam splitter. Here, in contrast, we demonstrate superresolving phase measurements based on two-photon N00N states generated by quantum dot single-photon sources making use of the Hong-Ou-Mandel effect on a beam splitter. By means of pulsed resonance fluorescence of a charged exciton state, we achieve, in postselection, a quantum enhanced improvement of the precision in phase uncertainty, higher than prescribed by the standard quantum limit. An analytical description of the measurement scheme is provided, reflecting requirements, capability, and restraints of single-photon emitters in optical quantum metrology. Our results point toward the realization of a real-world quantum sensor in the near future.PostprintPostprintPeer reviewe
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