Bang–Bang Refocusing of a Qubit Exposed to Telegraph Noise

Solid state qubits promise the great advantage of being naturally scalable to large quantum computer architectures, but they also possess the significant disadvantage of being intrinsically exposed to many sources of noise in the macroscopic solid-state environment. With suitably chosen systems such as superconductors, many of sources of noise can be suppressed. However, imprecision in nanofabrication will inevitably induce defects and disorder, such as charged impurities in the device material or substrate. Such defects generically produce telegraph noise and can hence be modelled as bistable fluctuators. We demonstrate the possibility of the active suppression of such telegraph noise by bang–bang control through an exhaustive study of a qubit coupled to a single bistable fluctuator. We use a stochastic Schrödinger equation, which is solved both numerically and analytically. The resulting dynamics can be visualized as diffusion of a spin vector on the Bloch sphere. We find that bang–bang control suppresses the effect of a bistable fluctuator by a factor roughly equalling the ratio of the bang–bang period and the typical fluctuator period. Therefore, we show the bang–bang protocol works essentially as a high pass filter on the spectrum of such telegraph noise sources. This suggests how the influence of 1/f-noise ubiquitous to the solid state world could be reduced, as it is typically generated by an ensemble of bistable fluctuators. Finally, we develop random walk models that estimate the level of noise suppression resulting from imperfect bang–bang operations, such as those that cannot be treated as -function impulses and those that have phase and axis errors. PACS: 03.65.Yz, 03.67.Lx, 05.40.-a     

Modeling Computer Forensics Process from Workflow Perspective

Similar with software process, computer forensics process is also a complex process. There have been a lot of modeling technologies for planning, analyzing and documentation of computer forensics activities. Different from software process, the step order of forensics process is very important. Skipping any step or interchanging one step may lead to the illegality of the whole forensics process, so a precise process is critical. In this paper, Petri net is used to model the computer forensics process.     

Bang–bang principle for linear and non-linear Goursat–Darboux problems

In this paper, the bang-bang principle for a control system described by a system of non-linear (in control) non-autonomous partial differential equations of hyperbolic type (the so-called Goursat-Darboux problem) is proved. As a particular case the bang-bang principle for a linear system is obtained. The method used for the proof is based on some properties of the Aumann integral.     

Geometric phase as a determinant of a qubit�C environment coupling

We investigate the qubit geometric phase and its properties in dependence on the mechanism for decoherence of a qubit weakly coupled to its environment. We consider two sources of decoherence: dephasing coupling (without exchange of energy with environment) and dissipative coupling (with exchange of energy). Reduced dynamics of the qubit is studied in terms of the rigorous Davies Markovian quantum master equation, both at zero and non–zero temperature. For pure dephasing coupling, the geometric phase varies monotonically with respect to the polar angle (in the Bloch sphere representation) parameterizing an initial state of the qubit. Moreover, it is antisymmetric about some points on the geometric phase-polar angle plane. This is in distinct contrast to the case of dissipative coupling for which the variation of the geometric phase with respect to the polar angle typically is non-monotonic, displaying local extrema and is not antisymmetric. Sensitivity of the geometric phase to details of the decoherence source can make it a tool for testing the nature of the qubit–environment interaction.     

Critical Success Factors to Improve the Game Development Process from a Developer’s Perspective

The growth of the software game development industry is enormous and is gaining importance day by day. This growth imposes severe pressure and a number of issues and challenges on the game development community. Game development is a complex process, and one important game development choice is to consider the developer’s perspective to produce good-quality software games by improving the game development process. The objective of this study is to provide a better understanding of the developer’s dimension as a factor in software game success. It focuses mainly on an empirical investigation of the effect of key developer’s factors on the software game development process and eventually on the quality of the resulting game. A quantitative survey was developed and conducted to identify key developer’s factors for an enhanced game development process. For this study, the developed survey was used to test the research model and hypotheses. The results provide evidence that game development organizations must deal with multiple key factors to remain competitive and to handle high pressure in the software game industry. The main contribution of this paper is to investigate empirically the influence of key developer’s factors on the game development process.     

Bang–bang property for an uncertain saddle point problem

In this paper, we propose a bang–bang control model for a saddle point problem using the optimistic value criterion. By using equation of optimality in uncertain optimal control, a bang–bang control problem is investigated. And then, an example is given to illustrate our results.     

Geometric measure of quantum discord for a two-parameter class of states in a qubit–qutrit system under various dissipative channels

Quantum discord, as a measure of all quantum correlations, has been proposed as the key resource in certain quantum communication tasks and quantum computational models without containing much entanglement. Daki? et al. (Phys Rev Lett 105:190502, 2010) introduced a geometric measure of quantum discord (GMQD) and derived an explicit formula for any two-qubit state. Luo and Fu (Phys Rev A 82:034302, 2010) introduced another form of GMQD and derived an explicit formula for arbitrary state in a bipartite quantum system. However, the explicit analytical expression for any bipartite system was not given. In this work, we give out the explicit analytical expressions of the GMQD for a two-parameter class of states in a qubit–qutrit system and study its dynamics for the states under various dissipative channels in the first time. Our results show that all these dynamic evolutions do not lead to a sudden vanishing of GMQD. Quantum correlations vanish at an asymptotic time for local or multi-local dephasing, phase-flip, and depolarizing noise channels. However, it does not disappear even though t → ∞ for local trit-flip and local trit-phase-flip channels. Our results maybe provide some important information for the application of GMQD in hybrid qubit–qutrit systems in quantum information.     

Geometric Properties of Ribs and Fans of a Bezier Curve

Ribs and fans are interesting geometric entities that are derived from a given Bezier curve or surface based on the recent theory of rib and fan decomposition. In this paper, we present some of new geometric properties of ribs and fans for a Bezier curve including composite fans, rib-invariant deformation, and fan-continuity in subdivision. We also give some examples for the presented properties.     

Geometric criterion for the design of a non-oscillatory dynamical system†

The paper deals with responses of a non-linear multiple lumped dynamical system bounded in a large neighbourhood of the single, asymptotically stable equilibrium point. The sufficient, analytic criteria for the non-oscillation of such responses have been introduced in previous work (cf. Skowronaki and Shannon 1972). On the basis of the latter, the author discusses a geometric interpretation of necessary and sufficient criteria for non-oscillatory responses applied to the synthetic design of the relevant systems     

Quantum Computation: From a Programmer’s Perspective

This paper is the second part of a series of two articles on quantum computation. If the first part was mostly concerned with the mathematical formalism, here we turn to the programmer’s perspective. We analyze the various existing models of quantum computation and the problem of the stability of quantum information. We discuss the needs and challenges for the design of a scalable quantum programming language. We then present two interesting approaches and examine their strengths and weaknesses. Finally, we take a step back, and review the state of the research on the semantics of quantum computation, and how this can help in achieving some of the goals.     

Dynamic 3D surface reconstruction and motion modeling from a pan–tilt–zoom camera

3D surface reconstruction and motion modeling has been integrated in several industrial applications. Using a pan–tilt–zoom (PTZ) camera, we present an efficient method called dynamic 3D reconstruction (D3DR) for recovering the 3D motion and structure of a freely moving target. The proposed method estimates the PTZ measurements to keep the target in the center of the field of view (FoV) of the camera with the same size. Feature extraction and tracking approach are used in the imaging framework to estimate the target's translation, position, and distance. A selection strategy is used to select keyframes that show significant changes in target movement and directly update the recovered 3D information. The proposed D3DR method is designed to work in a real-time environment, not requiring all frames captured to be used to update the recovered 3D motion and structure of the target. Using fewer frames minimizes the time and space complexity required. Experimental results conducted on real-time video streams using different targets to prove the efficiency of the proposed method. The proposed D3DR has been compared to existing offline and online 3D reconstruction methods, showing that it uses less execution time than the offline method and uses an average of 49.6% of the total number of frames captured.     

Distance learning success – a perspective from socio-technical systems theory

With widespread adoption of computer-based distance education as a mission-critical component of the institution's educational program, the need for evaluation has emerged. In this research, we aim to expand on the systems approach by offering a model for evaluation based on socio-technical systems theory addressing a stated need in the literature for comprehensive models for evaluating e-learning environments (Holsapple, C.W. and Lee-Post, A., 2006 Holsapple, C. W. and Lee-Post, A. 2006. Defining, assessing, and promoting e-learning success: an information systems perspective. Decision Sciences Journal of Innovative Education, 4(1): 67–85. [Crossref] , [Google Scholar]. Defining, assessing, and promoting e-learning success: an information systems perspective. Decision Sciences Journal of Innovative Education, 4(1), 67–85). The proposed systems model evaluates distance learning success from the instructor's perspective. It defines and develops measures for course quality, system quality and corresponding impacts. The model is tested based on the data collected from 548 instructors of seven universities in the Midwest region of the USA. The results suggest that the proposed multi-dimensional system flexibility scale is reliable. The course quality significantly affects both system flexibility and faculty perceived impacts of distance education. The system flexibility also significantly affects both course quality and faculty perceived impacts.     

Computing a (1+ε)-Approximate Geometric Minimum-Diameter Spanning Tree

Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST) of P is a spanning tree of P such that the longest path through the tree is minimized. For several years, the best upper bound on the time to compute a GMDST was cubic with respect to the number of points in the input set. Recently, Timothy Chan introduced a subcubic time algorithm. In this paper we present an algorithm that generates a tree whose diameter is no more than (1 + ) times that of a GMDST, for any > 0. Our algorithm reduces the problem to several grid-aligned versions of the problem and runs within time $O(^-3+ n) and space O(n).     

Bang–bang control model with optimistic value criterion for uncertain switched systems

This paper studies an optimal control problem for uncertain switched linear systems with subsystems perturbed by uncertainty. A model for this problem is investigated with optimistic value criterion. The goal is to jointly design a deterministic switching law and a continuous feedback to optimize an uncertain objective function. A two-stage algorithm is applied to handle such model. In the first stage, the maximum value of the objective function and the bang–bang control are obtained under fixed switching instants, and in the second stage, GA and PSO algorithm are used to get the optimal switching instants, respectively. An example is shown to validate the method.     

Mobile recommendations based on interest prediction from consumer's installed apps–insights from a large-scale field study

Recommender systems are essential in mobile commerce to benefit both companies and individuals by offering highly personalized products and services. One key pre-requirement of applying such systems is to gain decent knowledge about each individual consumer through user profiling. However, most existing profiling approaches on mobile suffer problems such as non-real-time, intrusive, cold-start, and non-scalable, which prevents them from being adopted in reality. To tackle the problems, this work developed real-time machine-learning models to predict user profiles of smartphone users from openly accessible data, i.e. app installation logs. Results from a study with 904 participants showed that the models are able to predict interests on average 48.81% better than a random guess in terms of precision and 13.80% better in terms of recall. Since the effectiveness of such predictive models is unknown in practice, the predictive models were evaluated in a large-scale field experiment with 73,244 participants. Results showed that by leveraging our models, personalized mobile recommendations can be enabled and the corresponding click-through-rate can be improved by up to 228.30%. Supplementary information, study data, and software can be found at https://www.autoidlabs.ch/mobile-analytics.     

Deriving a Floyd–Hoare logic for non-local jumps from a formulæ-as-types notion of control

We derive a Floyd–Hoare logic for non-local jumps and mutable higher-order procedural variables from a formulæ-as-types notion of control for classical logic. A key contribution of this work is the design of an imperative dependent type system for Hoare triples, which corresponds to classical logic, but where the famous consequence rule is admissible. Moreover, we prove that this system is complete for a reasonable notion of validity for Hoare judgments.     

Improved Frankl–Rödl Theorem and Some of Its Geometric Consequences

We substantially improve a presently known explicit exponentially growing lower bound on the chromatic number of a Euclidean space with forbidden equilateral triangle. Furthermore, we improve an exponentially growing lower bound on the chromatic number of distance graphs with large girth. These refinements are obtained by improving known upper bounds on the product of cardinalities of two families of homogeneous subsets with one forbidden cross-intersection.     

Geometric Latent Dirichlet Allocation on a Matching Graph for Large-scale Image Datasets

Given a large-scale collection of images our aim is to efficiently associate images which contain the same entity, for example a building or object, and to discover the significant entities. To achieve this, we introduce the Geometric Latent Dirichlet Allocation (gLDA) model for unsupervised discovery of particular objects in unordered image collections. This explicitly represents images as mixtures of particular objects or facades, and builds rich latent topic models which incorporate the identity and locations of visual words specific to the topic in a geometrically consistent way. Applying standard inference techniques to this model enables images likely to contain the same object to be probabilistically grouped and ranked.     

Evasion of a moving object from detection by a system of observers: Sensor–maneuvering search means

Consideration was given to planning the optimal evasion trajectory of a moving object from the system of observers consisting of a sensor and initial and terminal points of the route. An optimization criterion was proposed. The optimal trajectory and the speed mode of the moving object were determined for sector and ring—the two zones of search for the maneuvering search means.