Three stage potassium vapor turbine test

Three-stage potassium vapor turbine test to determine effects of vapor wetness on impingement damage of different rotor blade material

Variational Characterisations of Separability and Entanglement of Formation

In this paper we develop a mathematical framework for the characterisation of separability and entanglement of formation (EoF) of general bipartite states. These characterisations are of the variational kind, meaning that separability and EoF are given in terms of a function which is to be minimized over the manifold of unitary matrices. A major benefit of such a characterisation is that it directly leads to a numerical procedure for calculating EoF. We present an efficient minimisation algorithm and an apply it to the bound entangled 3X3 Horodecki states; we show that their EoF is very low and that their distance to the set of separable states is also very low. Within the same variational framework we rephrase the results by Wootters (W. Wootters, Phys. Rev. Lett. 80, 2245 (1998)) on EoF for 2X2 states and present progress in generalising these results to higher dimensional systems.Comment: 11 pages RevTeX, 4 figure

Quasiclassical description of a superconductor with a spin density wave

We derive equations for the quasiclassical Green's functions $\check{g}$ within a simple model of a two-band superconductor with a spin-density-wave (SDW). The elements of the matrix $\check{g}$ are the retarded, advanced, and Keldysh functions each of which is an $8\times 8$ matrix in the Gor'kov-Nambu, the spin and the band space. In equilibrium, these equations are a generalization of the Eilenberger equation. On the basis of the derived equations we analyze the Knight shift, the proximity and the dc Josephson effects in the superconductors under consideration. The Knight shift is shown to depend on the orientation of the external magnetic field with respect to the direction of the vector of the magnetization of the SDW. The proximity effect is analyzed for an interface between a superconductor with the SDW and a normal metal. The function describing both superconducting and magnetic correlations is shown to penetrate the normal metal or a metal with the SDW due to the proximity effect. The dc Josephson current in an $S_{SDW}/N/S_{SDW}$ junction is also calculated as a function of the phase difference $\phi$. It is shown that in our model the Josephson current does not depend on the mutual orientation of the magnetic moments in the superconductors $S_{SDW}$ and is proportional to $\sin \phi$. The dissipationless spin current $j_{sp}$ depends on the angle $\alpha$ between the magnetization vectors in the same way ($j_{sp} \sim \sin \alpha$) and is not zero above the superconducting transition temperature.Comment: 13 pages, 2 figures. Typos corrected. Note in proof adde

Linear dynamic filtering with noisy input and output

Estimation problems for linear time-invariant systems with noisy input and output are considered. The smoothing problem is a least norm problem. An efficient algorithm using a Riccati-type recursion is derived. The equivalence between the optimal filter and an appropriately modified Kalman filter is established. The optimal estimate of the input signal is derived from the optimal state estimate. The result shows that the noisy input/output filtering problem is not fundamentally different from the classical Kalman filtering problem

Four qubits can be entangled in nine different ways

We consider a single copy of a pure four-partite state of qubits and investigate its behaviour under the action of stochastic local quantum operations assisted by classical communication (SLOCC). This leads to a complete classification of all different classes of pure states of four-qubits. It is shown that there exist nine families of states corresponding to nine different ways of entangling four qubits. The states in the generic family give rise to GHZ-like entanglement. The other ones contain essentially 2- or 3-qubit entanglement distributed among the four parties. The concept of concurrence and 3-tangle is generalized to the case of mixed states of 4 qubits, giving rise to a seven parameter family of entanglement monotones. Finally, the SLOCC operations maximizing all these entanglement monotones are derived, yielding the optimal single copy distillation protocol