Solving String Field Equations: New Uses for Old Tools

It is argued that the (NS-sector) superstring field equations are integrable, i.e. their solutions are obtainable from linear equations. We adapt the 25-year-old solution-generating "dressing" method and reduce the construction of nonperturbative superstring configurations to a specific cohomology problem. The application to vacuum superstring field theory is outlined.Comment: Talk presented by O.L. at the 35th International Symposium Ahrenshoop on the Theory of Elementary Particles, Berlin, Germany, 26-30 Aug 2002; v2: minor corrections, textheight adjuste

Mixed state geometric phases, entangled systems, and local unitary transformations

The geometric phase for a pure quantal state undergoing an arbitrary evolution is a ``memory'' of the geometry of the path in the projective Hilbert space of the system. We find that Uhlmann's geometric phase for a mixed quantal state undergoing unitary evolution not only depends on the geometry of the path of the system alone but also on a constrained bi-local unitary evolution of the purified entangled state. We analyze this in general, illustrate it for the qubit case, and propose an experiment to test this effect. We also show that the mixed state geometric phase proposed recently in the context of interferometry requires uni-local transformations and is therefore essentially a property of the system alone.Comment: minor changes, journal reference adde

New Impulses in the Forming of Magnesium Sheet Metals

Owing to growing demands by customers for comfort and safety in cars, the weight of the respective individual automobile increases constantly. Hence, the role of construction materials, such as aluminium and magnesium alloys in car body production becomes ever more important. Especially magnesium is highly attractive because of its small density, its positive mechanic-technological properties, and the ready availability as raw material. It is known that magnesium has a reduced formability at room temperature and needs to be heated up to temperatures at around 300°C to be deformable with technologically useful forming rates. So therefore to form sheets made of magnesium alloys, the workpiece has to be heated previously. The idea of combining the processes "inductive heating" and "pulsed magnetic forming" led to the following research work. The aim was to develop a tool that combines both processes to be able to heat up the forming zone at the workpiece to a significant temperature and to form it afterwards without changing the tool. However, in order to manufacture sheet metal components from magnesium innovative manufacturing technologies are necessary. The Institute for Machine Tools and Factory Management (IWF) carries out research and develops solutions in the field of pulsed magnetic forming

Travelling-waves consistent with turbulence-driven secondary flow in a square duct

We present numerically determined travelling-wave solutions for pressure-driven flow through a straight duct with a square cross-section. This family of solutions represents typical coherent structures (a staggered array of counter-rotating streamwise vortices and an associated low-speed streak) on each wall. Their streamwise average flow in the cross-sectional plane corresponds to an eight vortex pattern much alike the secondary flow found in the turbulent regime

Asymptotics of Quantum Relative Entropy From Representation Theoretical Viewpoint

In this paper it was proved that the quantum relative entropy $D(\sigma \| \rho)$ can be asymptotically attained by Kullback Leibler divergences of probabilities given by a certain sequence of POVMs. The sequence of POVMs depends on $\rho$, but is independent of the choice of $\sigma$.Comment: LaTeX2e. 8 pages. The title was changed from "Asymptotic Attainment for Quantum Relative Entropy

Analogue of cosmological particle creation in an ion trap

We study phonons in a dynamical chain of ions confined by a trap with a time-dependent (axial) potential strength and demonstrate that they behave in the same way as quantum fields in an expanding/contracting universe. Based on this analogy, we present a scheme for the detection of the analogue of cosmological particle creation which should be feasible with present-day technology. In order to test the quantum nature of the particle creation mechanism and to distinguish it from classical effects such as heating, we propose to measure the two-phonon amplitude via the $2^{\rm nd}$ red side-band and to compare it with the one-phonon amplitude ($1^{\rm st}$ red side-band). PACS: 04.62.+v, 98.80.-k, 42.50.Vk, 32.80.Pj.Comment: 4 pages, 2 figure

Geometric observation for the Bures fidelity between two states of a qubit

In this Brief Report, we present a geometric observation for the Bures fidelity between two states of a qubit.Comment: 4 pages, 1 figure, RevTex, Accepted by Phys. Rev.

Connections and Metrics Respecting Standard Purification

Standard purification interlaces Hermitian and Riemannian metrics on the space of density operators with metrics and connections on the purifying Hilbert-Schmidt space. We discuss connections and metrics which are well adopted to purification, and present a selected set of relations between them. A connection, as well as a metric on state space, can be obtained from a metric on the purification space. We include a condition, with which this correspondence becomes one-to-one. Our methods are borrowed from elementary *-representation and fibre space theory. We lift, as an example, solutions of a von Neumann equation, write down holonomy invariants for cyclic ones, and ``add noise'' to a curve of pure states.Comment: Latex, 27 page

Time-resolved density correlations as probe of squeezing in toroidal Bose-Einstein condensates

I study the evolution of mean field and linear quantum fluctuations in a toroidal Bose-Einstein condensate, whose interaction strength is quenched from a finite (repulsive) value to zero. The azimuthal equal-time density-density correlation function is calculated and shows temporal oscillations with twice the (final) excitation frequencies after the transition. These oscillations are a direct consequence of positive and negative frequency mixing during non-adiabatic evolution. I will argue that a time-resolved measurement of the equal-time density correlator might be used to calculate the moduli of the Bogoliubov coefficients and thus the amount of squeezing imposed on a mode, i.e., the number of atoms excited out of the condensate.Comment: 18 pages, IOP styl