Advanced control with a Cooper-pair box: stimulated Raman adiabatic passage and Fock-state generation in a nanomechanical resonator

The rapid experimental progress in the field of superconducting nanocircuits gives rise to an increasing quest for advanced quantum-control techniques for these macroscopically coherent systems. Here we demonstrate theoretically that stimulated Raman adiabatic passage (STIRAP) should be possible with the quantronium setup of a Cooper-pair box. The scheme appears to be robust against decoherence and should be realizable even with the existing technology. As an application we present a method to generate single-phonon states of a nanomechnical resonator by vacuum-stimulated adiabatic passage with the superconducting nanocircuit coupled to the resonator

Tangles of superpositions and the convex-roof extension

We discuss aspects of the convex-roof extension of multipartite entanglement measures, that is, SL(2,\CC) invariant tangles. We highlight two key concepts that contain valuable information about the tangle of a density matrix: the {\em zero-polytope} is a convex set of density matrices with vanishing tangle whereas the {\em convex characteristic curve} readily provides a non-trivial lower bound for the convex roof and serves as a tool for constructing the convex roof outside the zero-polytope. Both concepts are derived from the tangle for superpositions of the eigenstates of the density matrix. We illustrate their application by considering examples of density matrices for two-qubit and three-qubit states of rank 2, thereby pointing out both the power and the limitations of the concepts.Comment: 7 pages, 5 figures, revtex

Flight/ground sample comparison relating to flight experiment M552, exothermic brazing

Comparisons were made between Skylab and ground-based specimens of nickel and stainless steel which were vacuum brazed using silver-copper-lithium alloy with various joint configurations. It was established that the absence of gravity greatly extends the scope of brazing since capillary flow can proceed without gravity interference. There was also evidence of enhanced transport, primarily in that liquid silver copper alloy dissolves nickel to a much greater extent in the zero gravity environment

Influence of Alkali Ions on Tribological Properties of Silicon Surface

Tribological properties of surfaces (friction, adhesion and wear) provide challenging limitations to the design of reliable machines on the micro- and nanometer scale as the surface to volume area increases and volume, mass and inertia of the mobile parts decrease. This study reports on the reduction in the friction force of silicon surfaces after the alkali metal ion exposure in the form of aqueous solutions. A scanning force microscope equipped with a liquid cell was used to investigate the friction force and the pull-off force of a flat silicon surface immersed in water and in different alkali metal chlorides solutions: LiCl, NaCl and CsCl. The concentration ranged from 0.1 up to 1000 µmol/l. The changes in the free surface energy of the initial surface and of the modified surfaces after drying were determined from contact angle measurements and from the acid–base adhesion theory. In both cases, in the liquid environment and after drying of the exposed silicon substrates in air, the friction force is reduced by approximately 50 %. Our results provide new, fundamental insight into the exchange of surface termination layers in particular for tribology. Also it is suggested to use the procedure as a low-cost alternative to improve the tribological properties of the silicon surface in particular in applications where lubricating fluids are not appropriate, e.g., in nanomachines and devices

Anisotropic unstable ion distribution functions downstream of the solar wind termination shock

International audienceIn this paper we demonstrate that solar wind ions, passing over the quasiperpendicular portion of the solar wind MHD termination shock, unavoidably develop strongly pronounced pitchangle anisotropies. In order to prove that, we solve the Boltzmann-Vlasov equation for the ions, kinetically describing the ion passage over the MHD structure of the shock. With the solution of the anisotropic downstream ion distribution function we may also calculate higher order velocity moments of this distribution enabling us to calculate anisotropic downstream ion pressures. From these latter results we derive the conclusion that in most likely cases the downstream ion distribution will be mirror-mode unstable and with its free thermal energy will effectively drive magnetosonic turbulences. We estimate the energy that is pumped into this turbulence until marginal stability is achieved. In this newly established intermediate quasi-equilibrium state, as we can show, one can find 35 to 50 percent of the original energy sitting in the thermal mode perpendicular to the magnetic field in the form of magnetosonic turbulences, perhaps already identified by Voyager-1 as downstream trains of magnetic holes and humps. We discuss several consequences of this new quasi-equilibrium MHD plasma state downsstream of the shock