1,228 research outputs found
Model of the optical emission of a driven semiconductor quantum dot: phonon-enhanced coherent scattering and off-resonant sideband narrowing
We study the crucial role played by the solid-state environment in
determining the photon emission characteristics of a driven quantum dot. For
resonant driving, we predict a phonon-enhancement of the coherently emitted
radiation field with increasing driving strength, in stark contrast to the
conventional expectation of a rapidly decreasing fraction of coherent emission
with stronger driving. This surprising behaviour results from thermalisation of
the dot with respect to the phonon bath, and leads to a nonstandard regime of
resonance fluorescence in which significant coherent scattering and the Mollow
triplet coexist. Off-resonance, we show that despite the phonon influence,
narrowing of dot spectral sideband widths can occur in certain regimes,
consistent with an experimental trend.Comment: Published version. 5 pages, 2 figures, plus 4 page supplement. Title
changed, figure 1 revised, various edits and additions to the tex
Hardcore classification: identifying play styles in social games using network analysis
In the social network of a web-based online game, all players are not equal. Through network analysis, we show that the community of players in a online social game is an example of a scale free small world network and that the growth of the player-base obeys a power law.
The community is centred around a minority group of ``hardcore" players who define the social environment for the game, and without whom the social network would collapse. Methods are discussed for identifying this critically important subset of players automatically through analysing social behaviours within the game
A holistic mathematical modelling and simulation for cathodic delamination mechanism – a novel and an efficient approach
This paper addresses a holistic mathematical design using a novel approach for understanding the mechanism of cathodic delamination. The approach employed a set of interdependent parallel processes with each process representing: cation formation, oxygen reduction and cation transport mechanism, respectively. Novel mathematical equations have been developed for each of the processes based on the observations recorded from experimentation. These equations are then solved using efficient time-iterated algorithms. Each process consists of distinct algorithms which communicate with each other using duplex channels carrying signals. Each signal represents a distinct delamination parameter. As a result of interdependency of various processes and their parallel behaviour, it is much easier to analyse the quantitative agreement between various delamination parameters. The developed modelling approach provides an efficient and reliable prediction method for the delamination failure. The results obtained are in good agreement with the previously reported experimental interpretations and numerical results. This model provides a foundation for the future research within the area of coating failure analysis and prediction
The role of situation awareness in accidents of large-scale technological systems
© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. In the last two decades, several serious accidents at large-scale technological systems that have had grave consequences, such as that at Bhopal, have primarily been attributed to human error. However, further investigations have revealed that humans are not the primary cause of these accidents, but have inherited the problems and difficulties of working with complex systems created by engineers. The operators have to comprehend malfunctions in real time, respond quickly, and make rapid decisions to return operational units to normal conditions, but under these circumstances, the mental workload of operators rises sharply, and a mental workload that is too high increases the rate of error. Therefore, cognivitive human features such as situation awareness (SA) - one of the most important prerequisite for decision-making - should be considered and analyzed appropriately. This paper applys the SA Error Taxonomy methodology to analyze the role of SA in three different accidents: (1) A runaway chemical reaction at Institute, West Virginia killing two employees, injuring eight people, and requiring the evacuation of more than 40,000 residents adjacent to the facility, (2) The ignition of a vapor cloud at Bellwood, Illinois that killed one person, injured two employees, and caused significant business interruption, and (3) An explosion at Ontario, California injuring four workers and caused extensive damage to the facility. In addition, the paper presents certain requirements for cognitive operator support system development and operator training under abnormal situations to promote operators' SA in the process industry
Efficient high-fidelity quantum computation using matter qubits and linear optics
We propose a practical, scalable, and efficient scheme for quantum
computation using spatially separated matter qubits and single photon
interference effects. The qubit systems can be NV-centers in diamond,
Pauli-blockade quantum dots with an excess electron or trapped ions with
optical transitions, which are each placed in a cavity and subsequently
entangled using a double-heralded single-photon detection scheme. The fidelity
of the resulting entanglement is extremely robust against the most important
errors such as detector loss, spontaneous emission, and mismatch of cavity
parameters. We demonstrate how this entangling operation can be used to
efficiently generate cluster states of many qubits, which, together with single
qubit operations and readout, can be used to implement universal quantum
computation. Existing experimental parameters indicate that high fidelity
clusters can be generated with a moderate constant overhead.Comment: 5 pages, 3 figures, broader introduction and improved scalability of
cluster state generatio
Phonon-Induced Rabi-Frequency Renormalization of Optically Driven Single InGaAs/GaAs Quantum Dots
The authors thank the EPSRC (U.K.) EP/G001642, and the QIPIRC U.K. for financial support. A. N. is supported by the EPSRC and B.W. L. by the Royal Society.We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse areas of up to 14 pi. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb shift.Peer reviewe
Long-lived spin entanglement induced by a spatially correlated thermal bath
We investigate how two spatially separated qubits coupled to a common heat
bath can be entangled by purely dissipative dynamics. We identify a dynamical
time scale associated with the lifetime of the dissipatively generated
entanglement and show that it can be much longer than either the typical
single-qubit decoherence time or the time scale on which a direct exchange
interaction can entangle the qubits. We give an approximate analytical
expression for the long-time evolution of the qubit concurrence and propose an
ion trap scheme in which such dynamics should be observable.Comment: 5 pages, 2 figure
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