Superabsorption of light via quantum engineering

Almost 60 years ago Dicke introduced the term superradiance to describe a signature quantum effect: N atoms can collectively emit light at a rate proportional to N^2. Even for moderate N this represents a significant increase over the prediction of classical physics, and the effect has found applications ranging from probing exciton delocalisation in biological systems, to developing a new class of laser, and even in astrophysics. Structures that super-radiate must also have enhanced absorption, but the former always dominates in natural systems. Here we show that modern quantum control techniques can overcome this restriction. Our theory establishes that superabsorption can be achieved and sustained in certain simple nanostructures, by trapping the system in a highly excited state while extracting energy into a non-radiative channel. The effect offers the prospect of a new class of quantum nanotechnology, capable of absorbing light many times faster than is currently possible; potential applications of this effect include light harvesting and photon detection. An array of quantum dots or a porphyrin ring could provide an implementation to demonstrate this effect

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

Screening nuclear field fluctuations in quantum dots for indistinguishable photon generation

A semiconductor quantum dot can generate highly coherent and indistinguishable single photons. However, intrinsic semiconductor dephasing mechanisms can reduce the visibility of two-photon interference. For an electron in a quantum dot, a fundamental dephasing process is the hyperfine interaction with the nuclear spin bath. Here we directly probe the consequence of the fluctuating nuclear spins on the elastic and inelastic scattered photon spectra from a resident electron in a single dot. We find the nuclear spin fluctuations lead to detuned Raman scattered photons which are distinguishable from both the elastic and incoherent components of the resonance fluorescence. This significantly reduces two-photon interference visibility. However, we demonstrate successful screening of the nuclear spin noise which enables the generation of coherent single photons that exhibit high visibility two-photon interference.Comment: 5 pages, 4 figures + Supplementary Informatio

A survey of obstetric complications and pregnancy outcomes in paediatric and nonpaediatric anaesthesiologists

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73884/1/j.1460-9592.2003.01079.x.pd

Individual Reactions of Permanganate and Various Reductants - Student Report to the DOE ERULF Program for Work Conducted May to July 2000

Tank waste on the Hanford Site contains radioactive elements that need to be removed from solution prior to disposal. One effective way to do this is to precipitate the radioactive elements with manganese solids, produced by permanganate oxidation. When added to tank waste, the permanganate reacts quickly producing manganese (IV) dioxide precipitate. Because of the speed of the reaction it is difficult to tell what exactly is happening. Individual reactions using non-radioactive reductants found in the tanks were done to determine reaction kinetics, what permanganate was reduced to, and what oxidation products were formed. In this project sodium formate, sodium nitrite, glycolic acid, glycine, and sodium oxalate were studied using various concentrations of reductant in alkaline sodium hydroxide solutions. It was determined that formate reacted the quickest, followed by glycine and glycolic acid. Oxalate and nitrite did not appear to react with the permanganate solutions. The products of the oxidation reaction were examined. Formate was oxidized to carbonate and water. Glycolic acid was oxidized slower producing oxalate and water. Glycine reactions formed some ammonia in solution, oxalate, and water. The research reported by Amber Gauger in this report was part of a DOE ERULF student intern program at Pacific Northwest National Laboratory under the direction of Richard Hallen in the summer of 2000

The Most Commonly Occurring Papillary Thyroid Cancer in the United States Is Now a Microcarcinoma in a Patient Older than 45 Years

Background: The incidence of papillary thyroid cancer (PTC) is growing at a faster rate than any other malignancy. However, it is unknown what effect age is having on the changing PTC incidence rates. With the goal of understanding the role of age in thyroid cancer incidence, this study analyzes the changing demographics of patients with PTC over the past three decades. Methods: This was a retrospective evaluation of the incidence rates of PTC from 1973 to 2006 reported by the National Cancer Institute's Surveillance, Epidemiology, and End Results database. Results: From 1973-2006 the age group most commonly found to have PTC has shifted from patients in their 30s to patients in the 40-50-year-old age group. In 1973 60% of PTC cases were found in patients younger than 45, and the majority of cases continued to occur in younger patients until 1999. After 1999 PTC became more common in patients older than 45 years, and in 2006, 61% of PTC cases were in patients older than 45 years. From 1988 to 2003 there has been an increasing incidence of all sizes of PTC in all age groups with the largest increase in tumors <1-cm in patients older than 45. Forty-three percent of tumors in patients older than 45 are now <1-cm, whereas only 34% are <1-cm in patients younger than 45. Of the nearly 20,000 thyroid cancer cases in 2003, 24% were microcarcinomas in patients over the age of 45. Conclusions: The incidence of PTC is increasing disproportionally in patients older than 45 years. The number of PTC tumors smaller than 1-cm is increasing in all age groups, and now the most commonly found PTC tumor in the United States is a microcarcinoma in a patient older than 45 years. These changing patterns relating age and incidence have important prognostic and treatment implications for patients with PTC.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90466/1/thy-2E2010-2E0137.pd

Eigen-AD: Algorithmic Differentiation of the Eigen Library

In this work we present useful techniques and possible enhancements when applying an Algorithmic Differentiation (AD) tool to the linear algebra library Eigen using our in-house AD by overloading (AD-O) tool dco/c++ as a case study. After outlining performance and feasibility issues when calculating derivatives for the official Eigen release, we propose Eigen-AD, which enables different optimization options for an AD-O tool by providing add-on modules for Eigen. The range of features includes a better handling of expression templates for general performance improvements, as well as implementations of symbolically derived expressions for calculating derivatives of certain core operations. The software design allows an AD-O tool to provide specializations to automatically include symbolic operations and thereby keep the look and feel of plain AD by overloading. As a showcase, dco/c++ is provided with such a module and its significant performance improvements are validated by benchmarks.Comment: Updated with accepted version for ICCS 2020 conference proceedings. The final authenticated publication is available online at https://doi.org/10.1007/978-3-030-50371-0_51. See v1 for the original, extended preprint. 14 pages, 7 figure

Hydrodynamic Synchronisation of Model Microswimmers

We define a model microswimmer with a variable cycle time, thus allowing the possibility of phase locking driven by hydrodynamic interactions between swimmers. We find that, for extensile or contractile swimmers, phase locking does occur, with the relative phase of the two swimmers being, in general, close to 0 or pi, depending on their relative position and orientation. We show that, as expected on grounds of symmetry, self T-dual swimmers, which are time-reversal covariant, do not phase-lock. We also discuss the phase behaviour of a line of tethered swimmers, or pumps. These show oscillations in their relative phases reminiscent of the metachronal waves of cilia.Comment: 17 pages, 8 figure