Event-by-event Simulation of Quantum Cryptography Protocols

We present a new approach to simulate quantum cryptography protocols using event-based processes. The method is validated by simulating the BB84 protocol and the Ekert protocol, both without and with the presence of an eavesdropper

The influences of surface temperature on upwellings in planetary convection with phase transitions

The importance of surface temperature for mantle convection appears with the presence of adiabatic heating and cooling and the release and consumption of latent heat in the presence of phase transitions. For some planetary bodies these effects cannot be neglected. The dimensionless surface temperature T0, which is the ratio between the temperature at the top of the convective region and the temperature drop across the mantle, is close to one for Mars and Venus. For the Earth, T0 lies between 0.2 and 0.5. The dynamical influence of T0 is especially poignant for internally heated convection with temperature-dependent viscosity. There is a tight coupling between the magnitude of the temperature field and the viscosity itself. We have studied temperature-dependent viscosity convection for both low-T0 (0.2) and high-T0 (1.2) situations and with internal heating in mantle convection with two upper-mantle phase transitions. Our results show that within this range of T0 there exist two regimes for the evolution of upwellings in the mantle. In transient situations plumeplume collisions lead to the formation of megaplumes for high-T0 regimes but are less likely to do so for low T0. In the long-term regime, plumes with low T0 are prone to develop from the transition zone with a supply of hot material coming from the shallow lower mantle. In systems with high T0, however, long-lived plumes tend to have deeper mantle origins. In quasi-layered situations high T0 may act as a positive feed-back mechanism in inducing powerful hot upwellings into the upper mantle. Ó 1998 Elsevier Science B.V. All rights reserved

Phase field modelling of grain boundary premelting using obstacle potentials

We investigate the multi-order parameter phase field model of Steinbach and Pezzolla [I. Steinbach, F. Pezzolla, A generalized field method for multiphase transformations using interface fields, Physica D 134 (1999) 385-393] concerning its ability to describe grain boundary premelting. For a single order parameter situation solid-melt interfaces are always attractive, which allows to have (unstable) equilibrium solid-melt-solid coexistence above the bulk melting point. The temperature dependent melt layer thickness and the disjoining potential, which describe the interface interaction, are affected by the choice of the thermal coupling function and the measure to define the amount of the liquid phase. Due to the strictly finite interface thickness also the interaction range is finite. For a multi-order parameter model we find either purely attractive or purely repulsive finite-ranged interactions. The premelting transition is then directly linked to the ratio of the grain boundary and solid-melt interfacial energy.Comment: 12 page

Electron shot noise beyond the second moment

The form of electron counting statistics of the tunneling current noise in a generic many-body interacting electron system is obtained. The third correlator of current fluctuations (the skewness of the charge counting distribution) has a universal relation with the current I and the quasiparticle charge q. This relation C_3 = q^2 I holds in a wide bias voltage range, both at large and small eV/kT, thereby representing an advantage compared to the Schottky formula. We consider the possibility of using the counting statistics for detecting quasiparticle charge at high temperature.Comment: 4 pages, 2 figure

Rf-induced transport of Cooper pairs in superconducting single electron transistors in a dissipative environment

We investigate low-temperature and low-voltage-bias charge transport in a superconducting Al single electron transistor in a dissipating environment, realized as on-chip high-ohmic Cr microstrips. In our samples with relatively large charging energy values Ec > EJ, where EJ is the energy of the Josephson coupling, two transport mechanisms were found to be dominating, both based on discrete tunneling of individual Cooper pairs: Depending on the gate voltage Vg, either sequential tunneling of pairs via the transistor island (in the open state of the transistor around the points Qg = CgVg = e mod(2e), where Cg is the gate capacitance) or their cotunneling through the transistor (for Qg away of these points) was found to prevail in the net current. As the open states of our transistors had been found to be unstable with respect to quasiparticle poisoning, high-frequency gate cycling (at f ~ 1 MHz) was applied to study the sequential tunneling mechanism. A simple model based on the master equation was found to be in a good agreement with the experimental data.Comment: 8 pages, 6 figure

Exciton-LO-phonon dynamics in InAs/GaAs quantum dots: Effects of zone-edge phonon damping

The dynamics of an exciton-LO-phonon system after an ultrafast optical excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of anharmonic phonon damping and its interplay with the phonon dispersion is analyzed. The signatures of the zone-edge decay process in the absorption spectrum and time evolution are highlighted, providing a possible way of experimental investigation on phonon anharmonicity effects.Comment: 10 pages, 2 figure

p-Adic Models of Ultrametric Diffusion Constrained by Hierarchical Energy Landscapes

We demonstrate that p-adic analysis is a natural basis for the construction of a wide variety of the ultrametric diffusion models constrained by hierarchical energy landscapes. A general analytical description in terms of p-adic analysis is given for a class of models. Two exactly solvable examples, i.e. the ultrametric diffusion constraned by the linear energy landscape and the ultrametric diffusion with reaction sink, are considered. We show that such models can be applied to both the relaxation in complex systems and the rate processes coupled to rearrangenment of the complex surrounding.Comment: 14 pages, 6 eps figures, LaTeX 2.0