Universal control induced by noise

On the basis of the quantum Zeno effect it has been recently shown [D. K. Burgarth et al., Nat. Commun. 5, 5173 (2014)] that a strong amplitude damping process applied locally on a part of a quantum system can have a beneficial effect on the dynamics of the remaining part of the system. Quantum operations that cannot be implemented without the dissipation become achievable by the action of the strong dissipative process. Here we generalize this idea by identifying decoherence-free subspaces (DFS's) as the subspaces in which the dynamics becomes more complex. Applying methods from quantum control theory we characterize the set of reachable operations within the DFS's. We provide three examples which become fully controllable within the DFS's while the control over the original Hilbert space in the absence of dissipation is trivial. In particular, we show that the (classical) Ising Hamiltonian is turned into a Heisenberg Hamiltonian by strong collective decoherence, which provides universal quantum computation within the DFS's. Moreover we perform numerical gate optimization to study how the process fidelity scales with the noise strength. As a byproduct a subsystem fidelity which can be applied in other optimization problems for open quantum systems is developed.Comment: 11 pages, 2 figure

VANET Coverage Analysis for GPS Augmentation Data in Rural Area

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Enhanced position accuracy is key for modern navigation systems, location based services and applications based on Inter-Vehicle Communication (IVC). Position data are the foundation for deriving vehicle trajectories used for assessing a situation's criticality in vehicle safety. Thus, especially Advanced Driver Assistance Systems (ADASs) and integral safety applications bene t from nearby vehicles spreading their positions periodically with high accuracy. Positioning based on Global Navigation Satellite System (GNSS) measurements can be enhanced by established Cooperative Positioning (CP) methods like Real-Time Kinematic (RTK) and Di fferential GNSS (DGNSS). Conventional CP relies on positioning correction data from a third party, whereas this paper introduces a self-su fficient CP system based on Precise Point Positioning (PPP) and Vehicular Ad-Hoc Network (VANET) technology requiring no infrastructure. Furthermore, the data dissemination process and achievable coverage are analysed by a simulation study for a rural area in Bavaria, Germany. For this purpose, the simulation employs the European IVC protocol stack ITS-G5. While the general feasibility of this CP approach could be assured, some remaining issues regarding employed network protocols were discovered as well

Improved Security Performance for VANET Simulations

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Upcoming deployments of Vehicular Ad Hoc Networks (VANETs) in Europe are expected to sign and verify packets secured by cryptographic signatures by default. Thus, when VANET simulations are used for development and test of applications building upon vehicular communication, the overhead induced by security extensions to the ITS-G5 protocol stack shall not be neglected. This paper presents a standard compliant simulation model capable to handle secured messages. Beside its suitability for Hardware-in-the-Loop simulations employing secured communication, the model's major advantage is the minimisation of the simulation environment's performance penalty linked with cryptographic computations

Building CPU stubs to optimize CPU bound systems: An application of dynamic performance stubs.

Dynamic performance stubs provide a framework for the simulation of the performance behavior of software modules and functions. Hence, they can be used as an exten- sion to software performance engineering methodologies. The methodology of dynamic performance stubs can be used for a gain oriented performance improvement. It is also possible to identify “hidden” bottlenecks and to prioritize optimization possibilities. Nowadays, the processing power of CPUs is mainly increased by adding more cores to the architecture. To have benefits from this, new software is mostly designed for parallel processing, especially, in large software projects. As software performance optimizations can be difficult in these environments, new methodologies have to be defined. This paper evaluates a possibility to simulate the functional behavior of software algorithms by the use of the simulated software functionality. These can be used by the dynamic performance stub framework, e.g., to build a CPU stub, to replace the algorithm. Thus, it describes a methodology as well as an implementation and evaluates both in an industrial case study. Moreover, it presents an extension to the CPU stubs by applying these stubs to simulate multi-threaded applications. The extension is evaluated by a case study as well. We show show that the functionality of software algorithms can be replaced by software simulation functions. This stubbing approach can be used to create dynamic performance stubs, such as CPU stubs. Additionally, we show that the concept of CPU stubs can be applied to multi-threaded applications

Dynamical decoupling of unbounded Hamiltonians

We investigate the possibility to suppress interactions between a finite dimensional system and an infinite dimensional environment through a fast sequence of unitary kicks on the finite dimensional system. This method, called dynamical decoupling, is known to work for bounded interactions, but physical environments such as bosonic heat baths are usually modelled with unbounded interactions, whence here we initiate a systematic study of dynamical decoupling for unbounded operators. We develop a sufficient decoupling criterion for arbitrary Hamiltonians and a necessary decoupling criterion for semibounded Hamiltonians. We give examples for unbounded Hamiltonians where decoupling works and the limiting evolution as well as the convergence speed can be explicitly computed. We show that decoupling does not always work for unbounded interactions and provide both physically and mathematically motivated examples.Comment: 18 pages, 3 figure

How To Improve . . . ISO/OSI Basic Reference Model

We present in an informal way the results of a formal specification of the ISO/OSI basic reference models service specifications. A new modular way of service specification which improves the reusability regarding different layers within a network is introduced. Some description techniques, which the ISO/OSI basic reference model uses, like time sequence diagrams, are clarified and improved. As a consequence the description of the ISO/OSI basic reference model gains a higher preciseness. Some ambiguities of the informal descriptions are removed by textual corrections