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

An efficient system for reliably transmitting image and video data over low bit rate noisy channels

This research project is intended to develop an efficient system for reliably transmitting image and video data over low bit rate noisy channels. The basic ideas behind the proposed approach are the following: employ statistical-based image modeling to facilitate pre- and post-processing and error detection, use spare redundancy that the source compression did not remove to add robustness, and implement coded modulation to improve bandwidth efficiency and noise rejection. Over the last six months, progress has been made on various aspects of the project. Through our studies of the integrated system, a list-based iterative Trellis decoder has been developed. The decoder accepts feedback from a post-processor which can detect channel errors in the reconstructed image. The error detection is based on the Huber Markov random field image model for the compressed image. The compression scheme used here is that of JPEG (Joint Photographic Experts Group). Experiments were performed and the results are quite encouraging. The principal ideas here are extendable to other compression techniques. In addition, research was also performed on unequal error protection channel coding, subband vector quantization as a means of source coding, and post processing for reducing coding artifacts. Our studies on unequal error protection (UEP) coding for image transmission focused on examining the properties of the UEP capabilities of convolutional codes. The investigation of subband vector quantization employed a wavelet transform with special emphasis on exploiting interband redundancy. The outcome of this investigation included the development of three algorithms for subband vector quantization. The reduction of transform coding artifacts was studied with the aid of a non-Gaussian Markov random field model. This results in improved image decompression. These studies are summarized and the technical papers included in the appendices

Hippocampal CA1 gamma power predicts the precision of spatial memory judgments.

The hippocampus plays a critical role in spatial memory. However, the exact neural mechanisms underlying high-fidelity spatial memory representations are unknown. We report findings from presurgical epilepsy patients with bilateral hippocampal depth electrodes performing an object-location memory task that provided a broad range of spatial memory precision. During encoding, patients were shown a series of objects along the circumference of an invisible circle. At test, the same objects were shown at the top of the circle (0°), and patients used a dial to move the object to its location shown during encoding. Angular error between the correct location and the indicated location was recorded as a continuous measure of performance. By registering pre- and postimplantation MRI scans, we were able to localize the electrodes to specific hippocampal subfields. We found a correlation between increased gamma power, thought to reflect local excitatory activity, and the precision of spatial memory retrieval in hippocampal CA1 electrodes. Additionally, we found a similar relationship between gamma power and memory precision in the dorsolateral prefrontal cortex and a directional relationship between activity in this region and in the CA1, suggesting that the dorsolateral prefrontal cortex is involved in postretrieval processing. These results indicate that local processing in hippocampal CA1 and dorsolateral prefrontal cortex supports high-fidelity spatial memory representations

The Ursinus Weekly, June 5, 1961

198 diplomas sum up 4 Ursinus years: Prizes bestowed on outstanding Ursinus students • Sandberg \u2761 valedictorian; Graduates summa cum laude • Four honorary degrees awarded this morning: Robert N. Hilkert delivers address to Ursinus\u27 198 senior graduates • Roadside billboard inspiration for Hilkert\u27s speech • Cash prize given four cited for teaching merit • Barbara Pine wins scholarship; Her blindness no obstacle • Biology instructor leaves to tie up loose ends • Amigo to retire; Students\u27 friend for eleven years • Dr. Paisley\u27s death saddens commencement; Board President served Ursinus for 51 years • Newspaperman elected new trustee board head • September may bring 280 freshmen; U.C. Admissions Department reports • New Weekly ad manager wins Wayne Brown prize • Editorial: Sharpened incisors; Good luck • Ursinus in the past • Art of understanding • Seniors submit post-graduation plans; Many teach, work for further degrees • Lacrosse players undefeated again; Trample Drexel • Snell softballers post 3-2 log; Ask more games • Intramural corner • Wait\u27ll next year when nine starters return to diamond • Lynne Crosley lacrosse all-American first team • Netmen competent despite 3-5 log; Famous is MVP • Sport page outlet for creativity, magazine writes • Track team tallies 5-5 \u2761 record; Wise made captain • Morgan finally defeated; Moran wins in AAU run • Mrs. Shryock to retire; Mrs. Bugelholl plans move • Ursinus professor to attend nuclear session • Organizations list late election results • Ursinus College gets $92,000 in Lehigh estate • Late track news: Morgan runs 4:04.2 in Boardwalk Mile • Dr. Creager reported doing well; Needs rest • Ursinus awarded$12,000 F. J. Clamer memorial fundhttps://digitalcommons.ursinus.edu/weekly/1344/thumbnail.jp

An entangled two photon source using biexciton emission of an asymmetric quantum dot in a cavity

A semiconductor based scheme has been proposed for generating entangled photon pairs from the radiative decay of an electrically-pumped biexciton in a quantum dot. Symmetric dots produce polarisation entanglement, but experimentally-realised asymmetric dots produce photons entangled in both polarisation and frequency. In this work, we investigate the possibility of erasing the `which-path' information contained in the frequencies of the photons produced by asymmetric quantum dots to recover polarisation-entangled photons. We consider a biexciton with non-degenerate intermediate excitonic states in a leaky optical cavity with pairs of degenerate cavity modes close to the non-degenerate exciton transition frequencies. An open quantum system approach is used to compute the polarisation entanglement of the two-photon state after it escapes from the cavity, measured by the visibility of two-photon interference fringes. We explicitly relate the two-photon visibility to the degree of Bell-inequality violation, deriving a threshold at which Bell-inequality violations will be observed. Our results show that an ideal cavity will produce maximally polarisation-entangled photon pairs, and even a non-ideal cavity will produce partially entangled photon pairs capable of violating a Bell-inequality.Comment: 16 pages, 10 figures, submitted to PR

Some comments on graduate training for engineers

QUESTIONING the value and adequacy of postgraduate engineering courses as commonly conducted, L. W. W. Morrow in an article in Electrical Engineering for March 1939, pages 118–22, called for a program of investigation of postgraduate training. Solicited comments of some representative industrialists and educators are presented here

Explorations, Vol. 2, No. 2

Cover: The painting reproduced on the cover is an oil on canvas entitled “Konrad Oberhuber’s Visit to Compass Harbor, Maine, ” by Michael Lewis, 1985. Lewis is Professor of Art at the University of Maine at Orono. ©Michael Lewis, 1985 Articles include: The Gulf of Maine: A Sea Beside a Sea, by Kathleen Lignell The Gulf of Maine Littoral world of promise, by Carole J. Bombard for David Sanger Marine Worms Worth Fifteen Dollars Each? by David Dean Free Trade, Not Trade War, by James A. Wilson Inner Space—The Gulf of Maine: its history and future for research, by Robert S. Steneck The Shape of Mud and Its Importance to Marine Animals, by Les Watling The Humble Herring gold-plated sardine, by David K. Stevenson Seismic Profiling: The Search for the Submerged Geological Record in the Gulf of Maine, by Daniel F. Belknap and Joseph T. Kelley Our Cover Artist: Michael Lewis In the Classroom, by Michael Brody Nobody Told the Bumblebee He Couldn\u27t Fly, by Herbert Hidu The Tie That Binds: technology and research, by Robert S. Steneck Diet Developments for the Maine Lobster, by Robert Bayer A Wet Desert: secrets of the salt marsh, by Gary M. King Maine Marshes, by George L. Jacobson Mya Arenaria: return of the clam, by Devon Phillips CES: commitment and action, by Devon Phillips EPSCoR benthic research, by Lawrence M. Mayer In the Field of Researc

Multicenter evaluation of computer automated versus traditional surveillance of hospital-acquired bloodstream infections

Objective.Central line–associated bloodstream infection (BSI) rates are a key quality metric for comparing hospital quality and safety. Traditional BSI surveillance may be limited by interrater variability. We assessed whether a computer-automated method of central line–associated BSI detection can improve the validity of surveillance.Design.Retrospective cohort study.Setting.Eight medical and surgical intensive care units (ICUs) in 4 academic medical centers.Methods.Traditional surveillance (by hospital staff) and computer algorithm surveillance were each compared against a retrospective audit review using a random sample of blood culture episodes during the period 2004–2007 from which an organism was recovered. Episode-level agreement with audit review was measured with κ statistics, and differences were assessed using the test of equal κ coefficients. Linear regression was used to assess the relationship between surveillance performance (κ) and surveillance-reported BSI rates (BSIs per 1,000 central line–days).Results.We evaluated 664 blood culture episodes. Agreement with audit review was significantly lower for traditional surveillance (κ [95% confidence interval (CI)] = 0.44 [0.37–0.51]) than computer algorithm surveillance (κ [95% CI] [0.52–0.64]; P = .001). Agreement between traditional surveillance and audit review was heterogeneous across ICUs (P = .001); furthermore, traditional surveillance performed worse among ICUs reporting lower (better) BSI rates (P = .001). In contrast, computer algorithm performance was consistent across ICUs and across the range of computer-reported central line–associated BSI rates.Conclusions.Compared with traditional surveillance of bloodstream infections, computer automated surveillance improves accuracy and reliability, making interfacility performance comparisons more valid.Infect Control Hosp Epidemiol 2014;35(12):1483–1490</jats:sec

Exoplanet phase curves: observations and theory

Phase curves are the best technique to probe the three dimensional structure of exoplanets' atmospheres. In this chapter we first review current exoplanets phase curve observations and the particular challenges they face. We then describe the different physical mechanisms shaping the atmospheric phase curves of highly irradiated tidally locked exoplanets. Finally, we discuss the potential for future missions to further advance our understanding of these new worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been updated with new values for WASP-103b and WASP-18b. Contains a table sumarizing phase curve observation