Two-Phase Region of the Vortex-Solid Melting Transition: 3D XY Theory

In clean enough samples of the high-$T_c$ oxide materials, the phase transition into the superconducting state occurs along a first order line in the $H$-$T$ plane. This means that a two-phase region occurs in the B-$T$ plane, in which the liquid and solid vortex phases coexist. We discuss the thermodynamics of this two-phase region, developing formulae relating experimental quantities of interest. We then apply the 3D XY scaling theory to the problem, obtaining detailed predictions for the boundaries of the coexistence region. By using published data, we are able to predict the width of the two-phase region, and determine the physical parameters involved in the 3D XY description.Comment: 5 pages LaTeX, 1 .eps figure, uses epsf.st

Dynamic scaling of I-V data for the neutral 2D Coulomb gas

The value of the dynamic critical exponent z has been studied for experimental two-dimensional superconducting and Josephson Junction array systems in zero magnetic field via the Fisher-Fisher-Huse dynamic scaling analysis. We found z~5.6, a relatively large value indicative of non-diffusive dynamics. We extend this work here to simulational I-V curves that are also found to be characterized by the same large value of z.Comment: 2 pages, 2 embedded figures, LT22 proceedings, Physica

Detection and measurement of the Dzyaloshinskii-Moriya interaction in double quantum dot systems

Spins in quantum dots can act as the qubit for quantum computation. In this context we point out that spins on neighboring dots will experience an anisotropic form of the exchange coupling, called the Dzyaloshinskii-Moriya (DM) interaction, which mixes the spin singlet and triplet states. This will have an important effect on both qubit interactions and spin-dependent tunneling. We show that the interaction depends strongly on the direction of the external field, which gives an unambiguous signature of this effect. We further propose a new experiment using coupled quantum dots to detect and characterize the DM interaction.Comment: Updated version. Submitted to Physical Review

Pseudo-digital quantum bits

Quantum computers are analog devices; thus they are highly susceptible to accumulative errors arising from classical control electronics. Fast operation--as necessitated by decoherence--makes gating errors very likely. In most current designs for scalable quantum computers it is not possible to satisfy both the requirements of low decoherence errors and low gating errors. Here we introduce a hardware-based technique for pseudo-digital gate operation. We perform self-consistent simulations of semiconductor quantum dots, finding that pseudo-digital techniques reduce operational error rates by more than two orders of magnitude, thus facilitating fast operation.Comment: 4 pages, 3 figure

Extended interface states enhance valley splitting in Si/SiO2

Interface disorder and its effect on the valley degeneracy of the conduction band edge remains among the greatest theoretical challenges for understanding the operation of spin qubits in silicon. Here, we investigate a counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight binding methods, we show that intrinsic interface states can hybridize with conventional valley states, leading to a large ground state energy gap. The effects of hybridization have not previously been explored in details for valley splitting. We find that valley splitting is enhanced in the presence of disordered chemical bonds, in agreement with recent experiments.Comment: 4 pages, 4 figure

Subsidiarity and Federalism: An Old Concept with Contemporary Relevance for Political Society

Historically human societies have never collectively organized, politically or socially, in any singular, standardized and/or universal way. Beginning with the Peace of Westphalia in 1647 the nation-state gradually proliferated as a legitimate manifestation of collective human organization at a global level. This proliferation has culminated in the standardization of a singular means of mobilizing and organizing human societies. The statist age that began in the 16th and 17th centuries consolidated and centralized the political power of the state. Divergent factions and regional power blocks within European states were discouraged, as politics became centralized at the national level. The proliferation of the nation-state represented the standardization of human political organization according to a single model. Given that there are, and have been, a variety of means by which humans identify and organize politically, this suggests that this universal acceptance and entrenchment of one model may be somewhat inappropriate. (author's abstract

Extended interface states enhance valley splitting in Si/SiO2

Interface disorder and its effect on the valley degeneracy of the conduction band edge remains among the greatest theoretical challenges for understanding the operation of spin qubits in silicon. Here, we investigate a counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight binding methods, we show that intrinsic interface states can hybridize with conventional valley states, leading to a large ground state energy gap. The effects of hybridization have not previously been explored in details for valley splitting. We find that valley splitting is enhanced in the presence of disordered chemical bonds, in agreement with recent experiments.Comment: 4 pages, 4 figure