Forster signatures and qubits in optically driven quantum dot molecules

An interesting approach to achieve quantum gate operations in a solid state device is to implement an optically driven quantum gate using two vertically coupled self-assembled quantum dots, a quantum dot molecule (QDM). We present a realistic model for exciton dynamics in InGaAs/GaAs QDMs under intense laser excitation and applied electric fields. The dynamics is obtained by solutions of the Lindblad master equation. A map of the dressed ground state as function of laser energy and applied electric field exhibits rich structure that includes excitonic anticrossings that permit the identification of the relevant couplings. The optical signatures of the dipole-dipole Forster energy transfer mechanism show as splittings of several (spatially) indirect excitonic lines. Moreover, we construct a model for exciton qubit rotations by adiabatic electric field cyclic sweeps into a Forster-tunneling regime which induces level anticrossings. The proposed qubit exhibits Rabi oscillations among two well defined exciton pairs as function of the residence time at the anticrossing.Comment: Paper presented in the International Conference on Electronic Properties of Two-dimensional Systems and Modulated Semiconductor Structures Genova Magazzini del Cotone, July 15-20 200

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

Implementation of a Heart Failure Quality Initiative in a Skilled Nursing Facility: Lessons Learned

Skilled nursing facilities (SNFs) are organizations that represent complex adaptive systems, offering barriers to the implementation of quality improvement (QI) initiatives. The current article describes the authors’ efforts to use the approach of reflective adaptive process to implement a new model of care (i.e., the Skilled Heart Unit Program) for effective heart failure (HF) care in one SNF. A team of stakeholders from the local hospital system and a local SNF was convened to design and implement this new model. Evaluation of the implementation processes confirmed the value of the implementation approach, which centered on team-based approaches, staff engagement, and flexibility of processes to respect the SNF’s needs and culture. Interviews with facility staff and the administrator revealed their perceptions that the strategy resulted in better HF care, enhanced teamwork between staff and clinicians, and improved staff job satisfaction. This work provides a unique blueprint of strategic QI implementation for patients with HF in the SNF setting

Vibronic resonances facilitate excited state coherence in light harvesting proteins at room temperature

Until recently it was believed that photosynthesis, a fundamental process for life on earth, could be fully understood with semi-classical models. However, puzzling quantum phenomena have been observed in several photosynthetic pigment-protein complexes, prompting questions regarding the nature and role of these effects. Recent attention has focused on discrete vibrational modes that are resonant or quasi-resonant with excitonic energy splittings and strongly coupled to these excitonic states. Here we unambiguously identify excited state coherent superpositions in photosynthetic light-harvesting complexes using a new experimental approach. Decoherence on the timescale of the excited state lifetime allows low energy (56 cm-1) oscillations on the signal intensity to be observed. In conjunction with an appropriate model, these oscillations provide clear and direct experimental evidence that the persistent coherences observed require strong vibronic mixing among excited states

Circular Arc Approximation by Quartic H-Bézier Curve

The quartic H-Bézier curve is used for the approximation of circular arcs. It has five control points and one positive real free parameter. The four control points are carried out b

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

Factors influencing severity in acute ischemic strokes

Background: Stroke severity is one of the factors that determines stroke related disability. We explored possible associations between stroke severity and commonly evaluated clinical parameters of stroke patients. Objective: To determine the relationships between clinical features including routine in- hospital investigations done in first 24 hours of admission and variations in the stroke severity. Patients and Methods: This was a retrospective, analytical study performed in the Department of Neurology at Shifa International Hospital, Shifa Tameer-e-Millat University, Islamabad, Pakistan. Adult patients admitted with ischemic stroke, over a period of 39 months, with Middle Cerebral Artery infarctions, were included. National Institute of Heath Stroke Scale (NIHSS) score was taken as a measure of stroke severity. The pertinent information was filled in a predesigned data sheet, and analyzed using SPSS version 20.0. Results: A total of 207 patients were included in the study. The highest stroke severity was found in old age ([\u3e64 years]), and patients with cardio embolic and unclassified (\u3e one etiology) strokes, while the lowest severity was found in small artery occlusion strokes. Higher fasting serum triglyceride levels were associated with lower stroke severity and vice versa ([P=.002]). Among supra aortic large artery atherosclerosis the pre-stroke anti-platelet ([52 %]) and beta blocker use ([53.6 %]) was significantly associated with lower stroke severity. In cardio embolic strokes active smoking was associated with increased severity ([90%]). Conclusion: Stroke severity is not only related to stroke etiology, but also, age, fasting serum triglyceride levels, active smoking and pre-stroke medications may also play significant roles. Nevertheless, further studies are required with prospective design, to confirm our findings

Evaluation of thermodynamics, formation energetics and electronic properties of vacancy defects in CaZrO3

Using first-principles total energy calculations we have evaluated the thermodynamics and the electronic properties of intrinsic vacancy defects in orthorhombic CaZrO3. Charge density calculations and the atoms-in-molecules concept are used to elucidate the changes in electronic properties of CaZrO3 upon the introduction of vacancy defects. We explore the chemical stability and defect formation energies of charge-neutral as well as of charged intrinsic vacancies under various synthesis conditions and also present full and partial Schottky reaction energies. The calculated electronic properties indicate that hole-doped state can be achieved in charge neutral Ca vacancy containing CaZrO3 under oxidation condition, while reduction condition allows to control the electrical conductivity of CaZrO3 depending on the charge state and concentration of oxygen vacancies. The clustering of neutral oxygen vacancies in CaZrO3 is examined as well. This provides useful information for tailoring the electronic properties of this material. We show that intentional incorporation of various forms of intrinsic vacancy defects in CaZrO3 allows to considerably modify its electronic properties, making this material suitable for a wide range of applications