Quantum cryptography as a retrodiction problem

We propose a quantum key distribution protocol based on a quantum retrodiction protocol, known as the Mean King problem. The protocol uses a two way quantum channel. We show security against coherent attacks in a transmission error free scenario, even if Eve is allowed to attack both transmissions. This establishes a connection between retrodiction and key distribution.Comment: 5 pages, 1 figur

Shell corrections for finite depth potentials: Particle continuum effects

Shell corrections of finite, spherical, one-body potentials are analyzed using a smoothing procedure which properly accounts for the contribution from the particle continuum, i.e., unbound states. Since the plateau condition for the smoothed single-particle energy seldom holds, a new recipe is suggested for the definition of the shell correction. The generalized Strutinsky smoothing procedure is compared with the results of the semi-classical Wigner-Kirkwood expansion. A good agreement has been found for weakly bound nuclei in the vicinity of the proton drip line. However, some deviations remain for extremely neutron-rich systems due to the pathological behavior of the semi-classical level density around the particle threshold.Comment: 18 pages, 8 figure

Propagation and spectral properties of quantum walks in electric fields

We study one-dimensional quantum walks in a homogeneous electric field. The field is given by a phase which depends linearly on position and is applied after each step. The long time propagation properties of this system, such as revivals, ballistic expansion and Anderson localization, depend very sensitively on the value of the electric field $\Phi$, e.g., on whether $\Phi/(2\pi)$ is rational or irrational. We relate these properties to the continued fraction expansion of the field. When the field is given only with finite accuracy, the beginning of the expansion allows analogous conclusions about the behavior on finite time scales.Comment: 7 pages, 4 figure

Quantum Walks with Non-Orthogonal Position States

Quantum walks have by now been realized in a large variety of different physical settings. In some of these, particularly with trapped ions, the walk is implemented in phase space, where the corresponding position states are not orthogonal. We develop a general description of such a quantum walk and show how to map it into a standard one with orthogonal states, thereby making available all the tools developed for the latter. This enables a variety of experiments, which can be implemented with smaller step sizes and more steps. Tuning the non-orthogonality allows for an easy preparation of extended states such as momentum eigenstates, which travel at a well-defined speed with low dispersion. We introduce a method to adjust their velocity by momentum shifts, which allows to investigate intriguing effects such as the analog of Bloch oscillations.Comment: 5 pages, 4 figure

Some selected simulation experiments with the European Commission's QUEST model

This paper presents a set of simulation experiments using the European Commission's QUEST model to evaluate the effects of policy impulses and permanent supply side shocks in the four major EU economies. The simulation analysis illustrates the transmission mechanisms of specific monetary and fiscal policy shocks as well as two examples of permanent supply shocks.QUEST model, supply side shocks, monetary and fiscal policy, R�ger, in 't Veld,

The virtual observatory service TheoSSA: Establishing a database of synthetic stellar flux standards. I. NLTE spectral analysis of the DA-type white dwarf G 191-B2B

H-rich, DA-type white dwarfs are particularly suited as primary standard stars for flux calibration. State-of-the-art NLTE models consider opacities of species up to trans-iron elements and provide reliable synthetic stellar-atmosphere spectra to compare with observation. We establish a database of theoretical spectra of stellar flux standards that are easily accessible via a web interface. In the framework of the Virtual Observatory, the German Astrophysical Virtual Observatory developed the registered service TheoSSA. It provides easy access to stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code. In case of the DA white dwarf G 191-B2B, we demonstrate that the model reproduces not only its overall continuum shape but also the numerous metal lines exhibited in its ultraviolet spectrum. TheoSSA is in operation and contains presently a variety of SEDs for DA white dwarfs. It will be extended in the near future and can host SEDs of all primary and secondary flux standards. The spectral analysis of G 191-B2B has shown that our hydrostatic models reproduce the observations best at an effective temperature of 60000 +/- 2000K and a surface gravity of log g = 7.60 +/- 0.05. We newly identified Fe VI, Ni VI, and Zn IV lines. For the first time, we determined the photospheric zinc abundance with a logarithmic mass fraction of -4.89 (7.5 times solar). The abundances of He (upper limit), C, N, O, Al, Si, O, P, S, Fe, Ni, Ge, and Sn were precisely determined. Upper abundance limits of 10% solar were derived for Ti, Cr, Mn, and Co. The TheoSSA database of theoretical SEDs of stellar flux standards guarantees that the flux calibration of all astronomical data and cross-calibration between different instruments can be based on the same models and SEDs calculated with different model-atmosphere codes and are easy to compare.Comment: 42 pages, 27 figure

A Supersymmetric Contribution to the Neutrino Mass Matrix and Breaking of mu-tau Symmetry

Supersymmetry broken by anomaly mediation suffers from tachyonic slepton masses. A possible solution to this problem results in "decoupling", i.e., the first two generations of sfermions are much heavier than the third one. We note that in this scenario a sizable loop-induced contribution to the neutrino mass matrix results. As an application of this scenario we take advantage of the fact that the decoupling evidently not obeys 2-3 generation exchange symmetry. In the neutrino sector, this 2-3 symmetry (or mu-tau symmetry) is a useful Ansatz to generate zero theta_{13} and maximal theta_{23}. The induced deviations from these values are given for some examples, thereby linking SUSY breaking to the small parameters (including possibly the solar mass splitting) of the neutrino sector.Comment: 5 pages, 1 figur