Quantum logic operations and creation of entanglement in a scalable superconducting quantum computer with long-range constant interaction between qubits

We consider a one-dimensional chain of many superconducting quantum interference devices (SQUIDs), serving as charge qubits. Each SQUID is coupled to its nearest neighbors through constant capacitances. We study the quantum logic operations and implementation of entanglement in this system. Arrays with two and three qubits are considered in detail. We show that the creation of entanglement with an arbitrary number of qubits can be implemented, without systematic errors, even when the coupling between qubits is not small. A relatively large coupling constant allows one to increase the clock speed of the quantum computer. We analytically and numerically demonstrate the creation of the entanglement for this case, which can be a good test for the experimental implementation of a relatively simple quantum protocol with many qubits. We discuss a possible application of our approach for implementing universal quantum logic for more complex algorithms by decreasing the coupling constant and, correspondingly, decreasing the clock speed. The errors introduced by the long-range interaction for the universal logic gates are estimated analytically and calculated numerically. Our results can be useful for experimental implementation of quantum algorithms using controlled magnetic fluxes and gate voltages applied to the SQUIDs. The algorithms discussed in this paper can be implemented using already existing technologies in superconducting systems with constant inter-qubit coupling.Comment: 24 page

Perturbation Theory for Quantum Computation with Large Number of Qubits

We describe a new and consistent perturbation theory for solid-state quantum computation with many qubits. The errors in the implementation of simple quantum logic operations caused by non-resonant transitions are estimated. We verify our perturbation approach using exact numerical solution for relatively small (L=10) number of qubits. A preferred range of parameters is found in which the errors in processing quantum information are small. Our results are needed for experimental testing of scalable solid-state quantum computers.Comment: 8 pages RevTex including 2 figure

Inflationary phase in Generalized Brans-Dicke theory

We find a solution for exponential inflation in a Brans-Dicke generalized model, where the coupling "constant " is variable. While in General Relativity the equation of state is p is equal to minus rho, here we find p proportional to rho, where the proportionality constant is smaller than -2/3. The negativity of cosmic pressure implies acceleration of the expansion, even with lambda < 0 >.Comment: International Journal of Theoretical Physics, to be publishe

Ground resonance analysis using a substructure modeling approach

A convenient and versatile procedure for modeling and analyzing ground resonance phenomena is described and illustrated. A computer program is used which dynamically couples differential equations with nonlinear and time dependent coefficients. Each set of differential equations may represent a component such as a rotor, fuselage, landing gear, or a failed damper. Arbitrary combinations of such components may be formulated into a model of a system. When the coupled equations are formed, a procedure is executed which uses a Floquet analysis to determine the stability of the system. Illustrations of the use of the procedures along with the numerical examples are presented

Pitfalls in the analysis of low-temperature thermal conductivity of high-Tc cuprates

Recently, it was proposed that phonons are specularly reflected below about 0.5 K in ordinary single-crystal samples of high-T_c cuprates, and that the low-temperature thermal conductivity should be analyzed by fitting the data up to 0.5 K using an arbitrary power law. Such an analysis yields a result different from that obtained from the conventional analysis, in which the fitting is usually restricted to a region below 0.15 K. Here we show that the proposed new analysis is most likely flawed, because the specular phonon reflection means that the phonon mean free path \ell gets LONGER than the mean sample width, while the estimated \ell is actually much SHORTER than the mean sample width above 0.15 K.Comment: 4 pages, 1 figure; manuscript for the Proceedings of LEHTSC2007 to be published in Journal of Physics: Conference Serie

The knowledge base of a profession: the case of social work

Journals are said to play an important role in the establishment of a knowledge base of a profession. Professions also use knowledge from other disciplines and are thereby interdisciplinary in character, using various ways of knowing. Using the social work profession as an example, empirical knowledge , as found in journals, was found to be only one source of knowledge in the profession's knowledge base . Social work as a profession also produces grey documents which are directly related to the social work experience. Grey documentation enables the dissemination of non-empirically based knowledge which is useful to the practicing professions . The use of both empirical knowledge via the journal and grey documentation requires an integrated approach in knowledge dissemination by archivists and information experts. The issue of prevailing altitudes of practitioners towards empirical knowledge and academicians towards grey documentation is raised. The role of the archivist and information expert as a facilitator in accepting knowledge as having a value in itself is proposed.Se afirma que las revistas desempeñan un papel importante para establecer la base de conocimientos de una profesión. Las profesiones utilizan también conocimientos procedentes de otras disciplinas y son, por tanto, de carácter interdisciplinar, al utilizar diversas formas de conocimiento. Tomando como ejemplo a los trabajadores sociales , el conocimiento empírico tal como aparece en las revistas resultó ser sólo una de sus fuentes de conocimiento. Esta profesión origina también literatura gris directamente relacionada con la experiencia en trabajos sociales. Dicha literatura gris permite la difusión de conocimientos sin base empírica, que son de utilidad para las profesiones aplicadas. El uso de conjunto del conocimiento empírico vía revistas y literatura gris requiere una integración por parte de archiveros y especialistas en información. Se plantea la cuestión de las actitudes de los profesionales prácticos frente al conocimiento empírico y de los académicos frente a la literatura gris. Se propone que el papel del archivero y del especialista en información consista en hacer que se acepte la información por su valor intrínseco

Sensitive linear response of an electron-hole superfluid in a periodic potential

We consider excitons in a two-dimensional periodic potential and study the linear response of the excitonic superfluid to an electromagnetic wave at low and high densities. It turns out that the static structure factor for small wavevectors is very sensitive to a change of density and temperature. It is a consequence of the fact that thermal fluctuations play a crucial role at small wavevectors, since exchanging the order of the two limits, zero temperature and vanishing wavevector, leads to different results for the structure factor. This effect could be used for high accuracy measurements in the superfluid exciton phase, which might be realized by a gated electron-hole gas. The transition of the exciton system from the superfluid state to a non-superfluid state and its manifestation by light scattering are discussed.Comment: 9 pages, 5 figure

Meanfield treatment of Bragg scattering from a Bose-Einstein condensate

A unified semiclassical treatment of Bragg scattering from Bose-Einstein condensates is presented. The formalism is based on the Gross-Pitaevskii equation driven by classical light fields far detuned from atomic resonance. An approximate analytic solution is obtained and provides quantitative understanding of the atomic momentum state oscillations, as well as a simple expression for the momentum linewidth of the scattering process. The validity regime of the analytic solution is derived, and tested by three dimensional cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy

We propose a solid-state nuclear spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field ($\sim 10$T) and at low temperature $\sim 1$K.Comment: 3pages RevTex including 2 figure