1,194 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
Anticrossings in Foerster Coupled Quantum Dots
We consider two coupled generic quantum dots, each modelled by a simple
potential which allows the derivation of an analytical expression for the
inter-dot Foerster coupling, in the dipole-dipole approximation. We investigate
the energy level behaviour of this coupled two-dot system under the influence
of an external applied electric field and predict the presence of anticrossings
in the optical spectra due to the Foerster interaction.Comment: 13 pages, 7 figures. Published version. Substantially revised, new
sections on decay rates, absorption spectra, and tunnelin
Coherent and incoherent dynamics in excitonic energy transfer: correlated fluctuations and off-resonance effects
We study the nature of the energy transfer process within a pair of coupled
two-level systems (donor and acceptor) subject to interactions with the
surrounding environment. Going beyond a standard weak-coupling approach, we
derive a master equation within the polaron representation that allows for
investigation of both weak and strong system-bath couplings, as well as
reliable interpolation between these two limits. With this theory, we are then
able to explore both coherent and incoherent regimes of energy transfer within
the donor-acceptor pair. We elucidate how the degree of correlation in the
donor and acceptor fluctuations, the donor-acceptor energy mismatch, and the
range of the environment frequency distribution impact upon the energy transfer
dynamics. In the resonant case (no energy mismatch) we describe in detail how a
crossover from coherent to incoherent transfer dynamics occurs with increasing
temperature [A. Nazir, Phys. Rev. Lett. 103, 146404 (2009)], and we also
explore how fluctuation correlations are able to protect coherence in the
energy transfer process. We show that a strict crossover criterion is harder to
define when off-resonance, though we find qualitatively similar population
dynamics to the resonant case with increasing temperature, while the amplitude
of coherent population oscillations also becomes suppressed with growing site
energy mismatch.Comment: 14 pages, 7 figures, builds upon PRL 103, 146404 (2009)
(arXiv:0906.0592). Comments welcome. V2 - Section IV shortened to improve
presentation, references updated, new Imperial College affiliation added for
A. Nazir. Published versio
Maximising the interfacial toughness of thin coatings and substrate through optimisation of defined parapmeters
The influence of three parameters, i.e. interfacial roughness λ, coating thickness h and impurity radius r at the coating–substrate interface on interfacial toughness, has been investigated within the framework of two approaches, i.e. thermodynamics and fracture mechanics. The governing equations for both the approaches have been derived independently and then fused to form a governing law for evaluating the interfacial toughness. The analysis in this paper which considers three parameters (λ, h and r) has been divided into three setups. Each setup is used to analyse the effect of one variable parameter on interfacial toughness while keeping the other two parameters constant. Three samples for each setup were prepared considering the requirements of constant and variable parameters for each setup. Simulation techniques founded on the experimental studies have been developed during this research in order to find the optimised values of three parameters. These optimised values act as critical values (boundary point) between coating fail-safe and coating fail conditions. The experiment employed ASTM-B117 test, which is used to analyse the interfacial toughness of samples under each setup. These experiments showed excellent, quantitative agreement with the simulation trends predicted by the theoretical model
A Predictive Model for Life Assessment of Automotive Exhaust Mufflers Subject to Internal Corrosion Failure due to Exhaust Gases Condensation
A study has been presented of pitting corrosion on internal walls of automotive exhaust muffler due to exhaust gases condensation. The problem mainly exists in the rear section of exhaust system close to tail end pipe such as muffler, especially when the temperature of muffler does not go up during short distance run or winter. The water vapor condenses on the muffler's inner wall in the form of water droplets. The dissolution of corrosive gases which are coming from internal combustion of engine as well as condensation of low-pH acidic vapors in the water droplet can cause severe pitting corrosion on standard exhaust steel. In this work, an experiment is reported for internal corrosion, by using mufflers as test bed subjected to different environmental conditions. Based on observations, a mechanistic model has been developed which involves three main techniques (i) the dropwise condensation technique predicts the condensation rate and is based on heat and mass transfer theory (ii) the species breakdown in the droplet is established through the main thermodynamic and chemical equilibrium (iii) the pitting corrosion involving pit depth is predicted using electrochemical kinetic reactions, species transport and chemical reactions occurring inside the droplet. Lastly, the accuracy of model has been validated by comparison between experimental and predicted results showing a good agreement
An Optimised Approach of Protecting and Sustaining Large Vehicle System
This article is a synopsis of our research and highlights the outcomes and its impact. It was conducted for the development of a sustainable approach to protect and sustain large vehicles in sheltered environment for their enhanced longevity. In this research various modes of failures linked directly or indirectly to the structural ageing of large vehicles were identified, measured, and analysed. Based upon the research conducted; A frame-work to retard structural failures and in-situ condition monitoring has been proposed with an objective to prolong the structural longevity cost effectively
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
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