Evolution of entanglement within classical light states

We investigate the evolution of quantum correlations over the lifetime of a multi-photon state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, non-degenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarisation splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded

Improved fidelity of triggered entangled photons from single quantum dots

We demonstrate the on-demand emission of polarisation-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realisation of a practical quantum dot source compatible with applications in quantum information.Comment: 9 pages. Paper is available free of charge at http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor source of triggered entangled photon pairs', R. M. Stevenson et al., Nature 439, 179 (2006

Determining the Dependence of Grain Boundary Mobility on Misorientation in High Purity Aluminum with Zirconium Additions

Aluminum alloys are used frequently for applications within the aerospace industry, creating a demand for finely tuned aluminum alloys that maximize a material property of interest (strength, toughness, etc.) and minimize weight. In order to formulate more complex alloys, it is important to understand how alloying elements affect the kinetics of grain growth in the solvent system. This study analyzes the effect of small concentrations of zirconium in high purity aluminum on grain growth during primary recrystallization by empirically determining the grain boundary mobility via measuring grain boundary velocity as well as stored energy within a sample and correlating grain boundary misorientation to mobility data. Grain boundary velocity is measured by annealing single crystal samples of deformed high purity aluminum with Zr additions in a box furnace and completing orientation imaging microscopy (OIM) scans that use electron back scattered diffraction (EBSD) patterns to index a lattice and create an inverse pole figure (IPF). This inverse pole figure assigns colors to orientations of crystalline grains and allows for the tracking of grain boundaries after subsequent heat treatments as well as for the acquisition of the misorientation at any given grain interface. TSL software allows for analysis of the EBSD data which can calculate the average subgrain size and average misorientation within a region to provide a stored energy term. This value is used in tandem with micro hardness measurements to estimate stored energy. With a measured grain boundary velocity and stored energy, it is possible to calculate grain boundary mobility and correlate mobility with grain boundary misorientation.Grain boundary Mobility is a useful parameter to metallurgists as a predictor of grain size after deformation and heat treatments. However, grain boundary mobility has a variety of variables that are subject to change with composition, and is thus difficult to calculate. As such, it is necessary to experimentally determine the grain boundary mobility in unexplored alloy compositions for modeling as well as processing. Alloying metals for use in industry requires knowledge of how alloying elements will alter the processing parameters used to generate a desired set of properties. Thus by determining the bulk grain boundary mobility of high purity aluminum samples with Zirconium additions via heat treatment, this work validates the combined use of EBSD and microhardness as a useful means of collecting data that replicates previous results obtained in the literature.Stored energy results obtained in this work align well with values in the literature obtained by Huang and Humphreys as well as values obtained from microhardness by Taheri as well as Huang, Tao and Lu. The dependence of grain boundary mobility on misorientation is also seen to correspond well with results in the past by Taheri, Gottstein and Rollett with boundaries near 40° having higher mobility than random HAGBs. Additionally, data found in this study aligns with results predicted by the effect of preferential Zr segregation observed by Taheri. However, the less prominent shift of peak mobility from 40° to higher misorientation as anneal temperature increases is in contrast with previous results, calling into question if there is a true difference in observed mobility peaks between 38° and 40°.M.S., Materials Engineering -- Drexel University, 201

Giant Stark effect in the emission of single semiconductor quantum dots

We study the quantum-confined Stark effect in single InAs/GaAs quantum dots embedded within a AlGaAs/GaAs/AlGaAs quantum well. By significantly increasing the barrier height we can observe emission from a dot at electric fields of -500 kV/cm, leading to Stark shifts of up to 25 meV. Our results suggest this technique may enable future applications that require self-assembled dots with transitions at the same energy

Mental health and the response to financial incentives: evidence from a survey incentives experiment

Although mental health disorders such as anxiety and depression are common, there is little research on whether individuals in poor mental health react differently from others to financial incentives. This paper exploits an experiment from the UK Understanding Society Innovation Panel to assess how the participation response to randomly-assigned financial incentives differs by mental health status. We find that individuals in good mental health are more likely to respond when offered a higher financial incentive, whereas those in poor mental health are indifferent to the increased incentive. We find no comparable differences for physical health

Cavity-enhanced radiative emission rate in a single-photon-emitting diode operating at 0.5 GHz

We report the observation of a Purcell enhancement in the electroluminescence decay rate of a single quantum dot, embedded in a microcavity light-emitting-diode structure. Lateral confinement of the optical mode was achieved using an annulus of low-refractive-index aluminium oxide, formed by wet oxidation. The same layer acts as a current aperture, reducing the active area of the device without impeding the electrical properties of the p-i-n diode. This allowed single photon electroluminescence to be demonstrated at repetition rates up to 0.5 GHz.Comment: 11 pages, 4 Figures. To be published in New Journal of Physic

Epidemiology of glenohumeral dislocation and subsequent instability in an urban population

Background: Glenohumeral dislocation is the most commonly encountered adult joint instability. The epidemiology in the United Kingdom and worldwide is unclear and often limited to young, active groups that are not representative of general populations. Information regarding epidemiology and outcome from a first dislocation is useful for trauma service planning and patient counseling. We calculated the incidence of shoulder instability after a first dislocation in our urban population and investigated predictors of recurrent instability. Methods: A prospectively collected trauma database was retrospectively examined to identify patients with a first-time dislocation. Demographics, subsequent dislocation, and instability details were collected from electronic patient records. Results: In a 38-month study period, 329 first dislocations occurred in a population of 475,147 with mean follow-up 28.5 months (range, 10-50 months). The overall incidence for first-time dislocations in this population was 21.9 per 100,000 population, of which 7.9% sustained a redislocation and 6.1% had further symptomatic instability. There were 18.8% with associated greater tuberosity fractures, 8.8% sustained a nerve injury, and 2.7% were posterior dislocations. A bimodal distribution was observed for males (peak incidence per 100,000 of 42.1 and 50.9 in 15-24 and ≥85 age groups, respectively), and unimodal for females (peak 45.7 in the 65-74 age group). Conclusion: We demonstrate a previously unreported burden of dislocation in older age groups and suggest a rate of recurrence lower than previously reported in the United Kingdom. The group aged 15 to 19 years was at the highest risk of recurrent dislocation and instability. Gender was not a significant predictor of instability