Universal quantum computing with correlated spin-charge states

We propose a universal quantum computing scheme in which the orthogonal qubit states $|0>$ and $|1>$ are identical in their single-particle spin and charge properties. Each qubit is contained in a single quantum dot and gate operations are induced all-electrically by changes in the confinement potential. Within the computational space, these qubits are robust against environmental influences that couple to the system through single-particle channels. Due to the identical spin and charge properties of the $|0>$, $|1>$ states, the lowest-order relaxation and decoherence rates $1/T_1$ and $1/T_2$, within the Born-Markov approximation, both vanish for a large class of environmental couplings. We give explicit pulse sequences for a universal set of gates (phase, $\pi/8$, Hadamard, \textsc{cnot}) and discuss state preparation, manipulation, and detection.Comment: 6 pages, 3 eps figures, revtex

Nonlinear sigma Model Treatment of Quantum Antiferromagnets in a Magnetic Field

We present a theoretical analysis of the properties of low-dimensional quantum antiferromagnets in applied magnetic fields. In a nonlinear sigma model description, we use a spin stiffness analysis, a 1/N expansion, and a renormalization group approach to describe the broken-symmetry regimes of finite magnetization, and, in cases of most interest, a low-field regime where symmetry is restored by quantum fluctuations. We compute the magnetization, critical fields, spin correlation functions, and decay exponents accessible by nuclear magnetic resonance experiments. The model is relevant to many systems exhibiting Haldane physics, and provides good agreement with data for the two-chain spin ladder compound CuHpCl.Comment: 14 pages, 6 figures, full paper to accompany cond-mat/980415

Decomposition and Gluing for Adiabatic Quantum Optimization

Farhi and others have introduced the notion of solving NP problems using adiabatic quantum com- puters. We discuss an application of this idea to the problem of integer factorization, together with a technique we call gluing which can be used to build adiabatic models of interesting problems. Although adiabatic quantum computers already exist, they are likely to be too small to directly tackle problems of interesting practical sizes for the foreseeable future. Therefore, we discuss techniques for decomposition of large problems, which permits us to fully exploit such hardware as may be available. Numerical re- sults suggest that even simple decomposition techniques may yield acceptable results with subexponential overhead, independent of the performance of the underlying device.Comment: 15 pages, many figure

Coherent rotations of a single spin-based qubit in a single quantum dot at fixed Zeeman energy

Coherent rotations of single spin-based qubits may be accomplished electrically at fixed Zeeman energy with a qubit defined solely within a single electrostatically-defined quantum dot; the $g$-factor and the external magnetic field are kept constant. All that is required to be varied are the voltages on metallic gates which effectively change the shape of the elliptic quantum dot. The pseudospin-1/2 qubit is constructed from the two-dimensional $S=1/2$, $S_z=-1/2$ subspace of three interacting electrons in a two-dimensional potential well. Rotations are created by altering the direction of the pseudomagnetic field through changes in the shape of the confinement potential. By deriving an exact analytic solution to the long-range Coulomb interaction matrix elements, we calculate explicitly the range of magnitudes and directions the pseudomagnetic field can take. Numerical estimates are given for {GaAs}.Comment: Restructured manuscript, more details shown (results unchanged); Six pages, revtex4; More info at http://soliton.phys.dal.c

Equity Valuation : United States Steel Corporation

This dissertation aims to determine the price target of United States Steel Corporation, a steel manufacturing company of historical significance which has recently experienced profitability issues. Despite previous issues the company finds itself in a transitionary environment towards sustainability, presenting a unique opportunity for the company to rebound from several years of financial mediocracy compared to its peers. In pursue of the fair value of U.S. Steel two model will be utilized, for the fundamental analysis a DCF model will be performed and for the relative valuation a Comparable Company Analysis (CCA) also known as a multiple’s valuation. Within the DCF three scenarios will be computed to depict the different economic environments that the company may undergo, with those being an optimistic, a recession and a base scenario. For each respective scenario, assumptions have been made which conform with the company strategy and macro-economic landscape. Following the research and assumptions considered the price target for U.S. Steel comes to $17.1 per share, categorized as a sell recommendation, due to the target being 20trading price of$21.36 per share.Esta dissertação tem por objetivo determinar o preço-alvo da United States Steel Corporation, uma empresa siderúrgica de importância histórica que recentemente tem tido problemas de rentabilidade. Apesar destes problemas, a empresa encontra-se num ambiente de transição para a sustentabilidade, apresentando uma oportunidade única para recuperar de vários anos de mediocracia financeira em comparação com os seus concorrentes. Para determinar o valor justo da U.S. Steel, serão utilizados dois modelos: para a análise fundamental, será utilizado um modelo de Discounted Cash Flow e, para a avaliação relativa, uma análise de empresas comparáveis (CCA), também conhecida como avaliação por múltiplos. No âmbito do DCF, serão calculados três cenários para representar os diferentes ambientes económicos que a empresa pode atravessar, sendo estes um cenário optimista, um de recessão e um cenário base. Para cada um dos respetivos cenários, foram feitas suposições que estão em conformidade com a estratégia da empresa e o panorama macroeconómico. Após a pesquisa e os pressupostos considerados, o preço-alvo para a U.S. Steel é de $17,1 por acção, categorizado como uma recomendação de venda, devido ao facto de o preço-alvo ser 20inferior ao preço de negociação de$21,36 por acção

Why was it important for the Byzantines to read Latin? The views of Demetrios Kydones (1324-1398)

Abstract: Fourteenth-century Byzantium witnessed civil wars between cliques of the ruling elite, constant financial crisis and dramatic territorial reduction. As a result of two catastrophic civil wars that were fought in 1321-1328 and 1341-1347, the Byzantine empire evolved into a small state which was struggling to survive and defend itself against large numbers of hostile neighbours, some of whom had or gradually acquired the resources to develop military forces far superior to those of Byzantium. In the 1350s and1360s the Ottoman Turks began the conquest of European territories that belonged to the Byzantine empire and threatened the very existence of the Byzantine state. Seeing that it was impossible to face the Ottomans militarily many Byzantines began to support the idea of a Crusade against the Ottomans and the reconciliation between the Orthodox and the Catholic Churches. One of the most staunchest supporters of this policy was the prolific author and politician Demetrios Kydones. This article will discuss how Kydones promoted the policy of reconciliation and alliance with Western European powers against the Ottomans