Influence of electron-acoustic phonon scattering on intensity power broadening in a coherently driven quantum-dot cavity system

We present a quantum optics formalism to study intensity power broadening of a semiconductor quantum dot interacting with an acoustic phonon bath and a high $Q$ microcavity. Power broadening is investigated using a time-convolutionless master equation in the polaron frame which allows for a nonperturbative treatment of the interaction of the quantum dot with the phonon reservoir. We calculate the full non-Lorentzian photoluminescence (PL) lineshapes and numerically extract the intensity linewidths of the quantum dot exciton and the cavity mode as a function of pump rate and temperature. For increasing field strengths, multiphonon and multiphoton effects are found to be important, even for phonon bath temperatures as low as 4 K. We show that the interaction of the quantum dot with the phonon reservoir introduces pronounced features in the power broadened PL lineshape, enabling one to observe clear signatures of electron-phonon scattering. The PL lineshapes from cavity pumping and exciton pumping are found to be distinctly different, primarily since the latter is excited through the exciton-phonon reservoir. To help explain the underlying physics of phonon scattering on the power broadened lineshape, an effective phonon Lindblad master equation derived from the full time-convolutionless master equation is introduced; we identify and calculate distinct Lindblad scattering contributions from electron-phonon interactions, including effects such as excitation-induced dephasing, incoherent exciton excitation and exciton-cavity feeding. Our effective phonon master equation is shown to reproduce the full intensity PL and the phonon-coupling effects very well, suggesting that its general Lindblad form may find widespread use in semiconductor cavity-QED.Comment: To be published in PR

Managing engineering design in complex supply chains

The trend towards organising design, development and manufacture via supply chains, rather than predominantly in-house, poses major challenges for design management. Procurement methods based on adversarial competitive tendering are generally unsuited to complex engineering products requiring strong design and development coordination. Literature on ‘supplier partnerships’ has largely overlooked the implications for managing design and development. This paper reports the results of a major project that focuses upon this issue, concentrating on practical case studies – from British Rail, Netherlands Railways, Rolls Royce and British Coal – that involve the management of ‘devolved’ engineering design by large business organisations. A spectrum of approaches from in-house to fully devolved design is described. It is concluded that there does not appear to be a single best approach for managing devolved design, but that appropriate approaches for an organisation depend on its location in the supply chain and its ability to manage organisational change

Factoring sustainability into the Higher Education product-service system

This paper summarises the findings of the first phase of a major study of the environmental impacts of an important service system - higher education (HE). The study assessed three methods of providing HE: conventional campus-based courses and distance/open learning courses using print-based and electronic delivery, with the following key findings. (1) On average, the distance taught Open University (OU) courses involved 90% less energy and CO2 emissions (per unit of study) than the campus based courses, mainly due to reductions in student travel and housing energy consumption, plus scale economies in campus site utilisation. (2) The OU e-learning course had over 20% higher environmental impacts than the print-based OU course, due to higher use of computing, paper consumption for printing web-based material, and extra home heating during Internet access. Programmes to reduce the environmental impacts of HE should be broadened beyond 'greening' the campus and the curriculum to include the impacts of student travel and housing. The study challenges claims that 'de-materialisation' and using ICT to provide services such as HE necessarily reduces environmental impacts. Service system environmental impacts depend mainly on its requirements for transport and a dedicated infrastructure of buildings and equipment. ICT will only benefit the environment if they reduce the service's requirements for these elements

People centred eco-design: consumer adoption of low and zero carbon products and systems

Literature review, research model and findings of exploratory empirical research on consumer adoption and effective use of low and zero carbon technologies ranging from a hybrid car to solar water heating systems

Getting warmer: a field trial of heat pumps

Given the lack of data on heat pump performance in customers’ homes, the Energy Saving Trust in partnership with the Open University undertook the first large-scale heat pump field trial in the UK to determine how heat pumps perform in real-life conditions. The year-long field trial monitored technical performance and customer behaviour observed at 83 sites across the UK. The findings provide valuable information about the factors that affect the success of a domestic heat pump installation. Instead of revealing outcomes along statistical grounds, or acting as a “brand-vs-brand” competition, the field trial findings provide a discussion of key points of interest to potential consumers, including: • Measured coefficient of performance (COP) and system efficiency • Installation practices (both system design and performance) • Customer behaviour (contribution by the Open University) • Heating patterns and average internal temperatures • Economics This report makes recommendations for consumers, installers, manufacturers and policy makers, and identifies areas that require additional investigation and research

Studies of two-phase intermittent flow in pipelines.

Imperial Users onl