Possible Stabilization Mechanism with Bulk and Branes SO(N) Yang-Mills for Closed Universes

Widrawn: The solutions presented in this work are not compatible with the equation of motion for g_{00}, which we did not properly verify. In the framework of this work, the only bulk solutions compatible with periodicity of the fifth dimension are constant fields. Also for a scalar field only constant solutions are obtained.Comment: withdrawn: see abstrac

Directly accessible entangling gates for capacitively coupled singlet-triplet qubits

The recent experimental advances in capacitively coupled singlet-triplet qubits, particularly the demonstration of entanglement, opens the question of what type of entangling gates the system's Hamiltonian can produce directly via a single square pulse. We address this question by considering the system's Hamiltonian from first principles and using the representation of its nonlocal properties in terms of local invariants. In the analysis we include the three different ways in which the system can be biased and their effect on the generation of entangling gates. We find that, in one of the possible biasing modes, the Hamiltonian has an especially simple form, which can directly generate a wide range of different entangling gates including the iSWAP gate. Moreover, using the complete form of the Hamiltonian we find that, for any biasing mode, a CNOT gate can be generated directly.Comment: 10 pages, 5 figure

Dynamically Correcting a CNOT Gate for any Systematic Logical Error

We derive a set of composite pulse sequences that generates CNOT gates and correct all systematic errors within the logical subspace to arbitrary order. These sequences are applicable for any two-qubit interaction Hamiltonian, and make no assumptions about the underlying noise mechanism except that it is constant on the timescale of the operation. We do assume access to error-free single-qubit gates, so single-qubit gate imperfections eventually limit the achievable fidelity. However, since single-qubit gates generally have much higher fidelities than two-qubit gates in practice, these pulse sequences offer useful dynamical correction for a wide range of coupled qubit systems.Comment: 4 + pages, and 2 pages of supplemental materia

Entanglement dynamics of two Ising-coupled qubits with nonperpendicular local driving fields

We present an approximate analytical solution to the dynamic equation of two Ising-coupled qubits with oscillating classical control fields that are nonperpendicular to the static drift fields. This is a situation that has recently arisen in some solid-state experiments. With our solution we derive the analytical expressions for the local invariants as well as the local rotations needed to isolate a purely nonlocal gate. This determines the set of parameters that are required to generate any entangling gate. Moreover, we use our results to describe a recent experimental work on capacitively coupled singlet-triplet qubits in GaAs and discuss possible differences for a similar device in silicon.Comment: 6 pages, 3 figure

SAdS black holes and spacetime atoms: a heuristic approach

In this work, both extended phase space and holographic equipartition approaches are employed to develop an exact Van der Waals description of non--rotating $D=4$ SAdS black holes as an ensemble of spacetime atoms. After a possible microscopical interaction model is introduced, statistical mechanics techniques, with certain heuristic gravitational constraints, are used to derive the equation of state and the Bekenstein--Hawking entropy. The procedure is generalized to the charged $D=4$ SAdS black hole and to arbitrary $D\ge 3$ dimensions for the uncharged cases.Comment: Accepted for publication in Gen. Rel. Gra

Reply to the comment on the paper "Thermodynamics of two-dimensional magneto nanoparticles (P. Vargas, D. Altbir, M.Knobel and D. Laroze)" by H. Buettner and Yu. Gaididei

It is shown that there is bi-stability in a two dimensional system consisting of non interacting magnetic nanoparticles with equal uniaxial anisotropies. It is also shown that bi-stability still remains in three dimensions. The only consideration is that the applied magnetic field has to be perpendicular to the anisotropy axis.Comment: 3 pages, 1 figur

A detailed analysis of dipolar interactions and analytical approximations in arrays of magnetic nanowires

The investigation of the role of interactions in magnetic wire arrays is complex and often subject to strong simplifications. In this paper we obtained analytical expressions for the magnetostatic interactions between wires and investigate the range of validity of dipole-dipole, first order and second order approximations. We also analyze the extension of the interwire magnetostatic interactions in a sample and found that the number of wires required to reach energy convergence in the array strongly depends on the relative magnetic orientation between the wires.Comment: 7 pages and 5 figure

Linear guided modes and Whitham-Boussinesq model for variable topogra

In this article we study two classical linear water wave problems, i) normal modes of infinite straight channels of bounded constant cross-section, and ii) trapped longitudinal modes in domains with unbounded constant cross-section. Both problems can be stated using linearized free surface potential flow theory, and our goal is to compare known analytic solutions in the literature to numerical solutions obtained using an ad-hoc but simple approximation of the non-local Dirichlet-Neumann operator for linear waves proposed in [vargas2016whitham]. To study normal modes in channels with bounded cross-section we consider special symmetric triangular cross-sections, namely symmetric triangles with sides inclined at $45^{\circ}$ and $60^{\circ}$ to the vertical, and compare modes obtained using the non-local Dirichlet-Neumann operator to known semi-exact analytic expressions by Lamb [lamb1932hydrodynamics], Macdonald [macdonald1893waves] , Greenhill [greenhill1887wave], Packham [packham1980small], and Groves [groves1994hamiltonian]. These geometries have slopping beach boundaries that should in principle limit the applicability of our approximate Dirichlet-Neumann operator. We nevertheless see that the operator gives remarkably close results for even modes, while for odd modes we have some discrepancies near the boundary. For trapped longitudinal modes in domains with an infinite cross-section we consider a piecewise constant depth profile and compare modes computed with the nonlocal operator modes to known analytic solutions of linearized shallow water theory by Miles [miles1972wave], Lin, Juang and Tsay [lin2001anomalous], see also [mei2005theory]. This is a problem of significant geophysical interest, and the proposed model is shows to give quantitatively similar results for the lowest trapped modes.Comment: Submitted to Wave Motion Journal, October, 201

Linear Whitham-Boussinesq modes in channels of constant cross-section

We study normal modes for the linear water wave problem in infinite straight channels of bounded constant cross-section. Our goal is to compare semianalytic normal mode solutions known in the literature for special triangular cross-sections, namely isosceles triangles of equal angle of 45 and 60 degrees, see Lamb [17], Macdonald [19] , Greenhill [11], Packham [23], and Groves [12], to numerical solutions obtained using approximations of the non-local Dirichlet-Neumann operator for linear waves, specifically an ad-hoc approximation proposed in [25], and a first order truncation of the systematic depth expansion by Craig, Guyenne, Nicholls, and Sulem [6]. We consider cases of transverse (i.e. 2-D) modes and longitudinal modes, i.e. 3-D modes with sinusoidal dependence in the longitudinal direction. The triangular geometries considered have slopping beach boundaries that should in principle limit the applicability of the approximate Dirichlet-Neumann operators. We nevertheless see that the approximate operators give remarkably close results for transverse even modes, while for odd transverse modes we have some discrepancies near the boundary. In the case of longitudinal modes, where the theory only yields even modes, the different approximate operators show more discrepancies for the first two longitudinal modes and better agreement for higher modes. The ad-hoc approximation is generally closer to exact modes away from the boundary.Comment: Submitted manuscript 2018. arXiv admin note: substantial text overlap with arXiv:1710.0478

Quasi-SU(3) truncation scheme for odd-even sd-shell nuclei

The quasi-SU(3) symmetry, as found in shell model calculations, refers to the dominance of the single particle plus quadrupole-quadrupole terms in the Hamiltonian used to describe well deformed nuclei, and to the subspace relevant in its diagonalization. It provides a very efficient basis truncation scheme. It is shown that a small number of SU(3) coupled irreps, those with the largest C_2 values within the direct product of the proton and neutron SU(3) irreps with spin 0 and 1 (for even number of particles), and spin 1/2 and 3/2 for (for odd number of nucleons), are enough to describe the low energy spectra and B(E2) transition strengths of 21Ne, 23Na and 25Mg. A simple but realistic Hamiltonian is employed. Results compare favorably both with experimental data and with full shell model calculations. Limitations and possible improvements of the schematic Hamiltonian are discussed.Comment: 29 pages and 9 postscript figures. Submited to Nucl. Phys.