Spintronics and Quantum Computing: Switching Mechanisms for Qubits

Quantum computing and quantum communication are remarkable examples of new information processing technologies that arise from the coherent manipulation of spins in nanostructures. We review our theoretical proposal for using electron spins in quantum-confined nanostructures as qubits. We present single- and two-qubit gate mechanisms in laterally as well as vertically coupled quantum dots and discuss the possibility to couple spins in quantum dots via exchange or superexchange. In addition, we propose a new stationary wave switch, which allows to perform quantum operations with quantum dots or spin-1/2 molecules placed on a 1D or 2D lattice.Comment: 6 pages, 3 EPS figures, Latex, to appear in Physica E, proceedings of the PASP2000 conference on the physics and application of spin-related phenomena in semiconductors, Sendai, Japan, 200

Conductance interaction identification by means of Boltzmann distribution and mutual information analysis in conductance-based neuron models

Conductance interaction identification by means of Boltzmann distribution and mutual information analysis in conductance-based neuron models

The peer model advantage in infants’ imitation of familiar gestures performed by differently aged models

Infants’ imitation of differently aged models has been predominately investigated with object-related actions and so far has lead to mixed evidence. Whereas some studies reported an increased likelihood of imitating peer models in contrast to adult models, other studies reported the opposite pattern of results. In the present study, 14-month-old infants were presented with four familiar gestures (e.g., clapping) that were demonstrated by differently aged televised models (peer, older child, adult). Results revealed that infants were more likely to imitate the peer model than the older child or the adult. This result is discussed with respect to a social function of imitation and the mechanism of imitating familiar behavior

Three-Dimensionally Confined Optical Modes in Quantum Well Microtube Ring Resonators

We report on microtube ring resonators with quantum wells embedded as an optically active material. Optical modes are observed over a broad energy range. Their properties strongly depend on the exact geometry of the microtube along its axis. In particular we observe (i) preferential emission of light on the inside edge of the microtube and (ii) confinement of light also in direction of the tube axis by an axially varying geometry which is explained in an expanded waveguide model.Comment: 5 pages, 4 figure

Quantized spin excitations in a ferromagnetic microstrip from microwave photovoltage measurements

Quantized spin excitations in a single ferromagnetic microstrip have been measured using the microwave photovoltage technique. Several kinds of spin wave modes due to different contributions of the dipole-dipole and the exchange interactions are observed. Among them are a series of distinct dipole-exchange spin wave modes, which allow us to determine precisely the subtle spin boundary condition. A comprehensive picture for quantized spin excitations in a ferromagnet with finite size is thereby established. The dispersions of the quantized spin wave modes have two different branches separated by the saturation magnetization.Comment: 4 pages, 3 figure

Demographic Aspects of Changes in the Soviet Pension System

The paper discusses the consequences of possible demographic changes in the USSR as a whole and at the regional level upon the pension system under different assumptions about retirement ages. Some general recommendations on changes in the pension system based on international experience are presented

Asymmetric I-V characteristics and magnetoresistance in magnetic point contacts

We present a theoretical study of the transport properties of magnetic point contacts under bias. Our calculations are based on the Keldish's non-equilibrium Green's function formalism combined with a self-consistent empirical tight-binding Hamiltonian, which describes both strong ferromagnetism and charging effects. We demonstrate that large magnetoresistance solely due to electronic effects can be found when a sharp domain wall forms inside a magnetic atomic-scale point contact. Moreover we show that the symmetry of the $I$-$V$ characteristic depends on the position of the domain wall in the constriction. In particular diode-like curves can arise when the domain wall is placed off-center within the point contact, although the whole structure does not present any structural asymmetry.Comment: 7 figures, submitted to PR

The repatriation of exclusive competences from EU in post-Brexit United Kingdom

EU law making involves areas as diverse as banking regulation, agriculture, the environment, consumer protection and employment rights. With the UK’s proposed withdrawal from the EU, these powers will be repatriated to the UK. The UK today differs from the UK which joined the European Economic Community in 1973, so the question arises as to where in the UK will powers be repatriated? The corollary to that question is; what is the UK today? Emerging from the political debate on post-Brexit repatriation of competences from the EU is a tension; between the UK Government’s unitary-state position and the effect and spirit of the respective devolution settlements in each of the Nations. From a legal perspective these very settlements contain within them a continuing conundrum, which the UK Government is attempting to side-line. The conundrum is that these settlements were built upon the UK’s continuing membership of the EU. The settlements give effect to the supremacy of EU law, by specific provisions prohibiting the devolved parliaments and assemblies (in Scotland, Wales and Northern Ireland) from legislating contrary to EU law. The terms of the settlements reveal not a one-to-one relationship between the UK Government and the devolved governments, but a three-sided relationship, in which many key powers and competences are exercised not in Westminster, nor in Edinburgh, Cardiff and Belfast, but by the EU. Alongside that conundrum is another. A common feature of all the devolved settlements, and subsequent amendments, is that significant policy competences are transferred to the devolved parliaments and assemblies. This paper suggests that Brexit will remove some of the foundations of these devolution settlements and effectively return the UK to a unitary state, with uncertain and potentially destabilising constitutional consequences. This paper explores constitutional arrangements within the United Kingdom. It considers the competencies of the legislatures within the UK; the Bill before the UK Parliament for exiting the European Union and provides a commentary on the Brexit negotiation process in relation to the legislatures within the UK. The position explored is that at the end of December 2017

Fluorescence excitation enhancement by waveguiding nanowires

The optical properties of vertical semiconductor nanowires can allow an enhancement of fluorescence from surface-bound fluorophores, a feature proven useful in biosensing. One of the contributing factors to the fluorescence enhancement is thought to be the local increase of the incident excitation light intensity in the vicinity of the nanowire surface, where fluorophores are located. However, this effect has not been experimentally studied in detail to date. Here, we quantify the excitation enhancement of fluorophores bound to a semiconductor nanowire surface by combining modelling with measurements of fluorescence photobleaching rate, indicative of the excitation light intensity, using epitaxially grown GaP nanowires. We study the excitation enhancement for nanowires with a diameter of 50-250 nm and show that excitation enhancement reaches a maximum for certain diameters, depending on the excitation wavelength. Furthermore, we find that the excitation enhancement decreases rapidly within tens of nanometers from the nanowire sidewall. The results can be used to design nanowire-based optical systems with exceptional sensitivities for bioanalytical applications

Structural and magnetic properties of Fe/ZnSe(001) interfaces

We have performed first principles electronic structure calculations to investigate the structural and magnetic properties of Fe/ZnSe(001) interfaces. Calculations involving full geometry optimizations have been carried out for a broad range of thickness of Fe layers(0.5 monolayer to 10 monolayers) on top of a ZnSe(001) substrate. Both Zn and Se terminated interfaces have been explored. Total energy calculations show that Se segregates at the surface which is in agreement with recent experiments. For both Zn and Se terminations, the interface Fe magnetic moments are higher than the bulk bcc Fe moment. We have also investigated the effect of adding Fe atoms on top of a reconstructed ZnSe surface to explore the role of reconstruction of semiconductor surfaces in determining properties of metal-semiconductor interfaces. Fe breaks the Se dimer bond formed for a Se-rich (2x1) reconstructed surface. Finally, we looked at the reverse growth i.e. growth of Zn and Se atoms on a bcc Fe(001) substrate to investigate the properties of the second interface of a magnetotunnel junction. The results are in good agreement with the theoretical and experimental results, wherever available.Comment: 7 pages, 8 figures, accepted for publication in PR