• Volume 8,Issue 3-4,2014 Table of Contents
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    • >Special Issue on Quantum Computation and Quantum Information Processing
    • Preface

      2014, 8(3-4):207-207.

      Abstract (2758) HTML (0) PDF 63.58 K (1747) Comment (0) Favorites

      Abstract:Quantum computation and quantum information processing, lying in the interdisciplinary field of computer science, mathematics and physics, is developing rapidly in recent years. This emerging and exciting field exploits quantum features in performing various information tasks, and opens new avenue for our information era. Quantum informatics exhibits many facets, ranging from quantum simulation to quantum computation, and including quantum cryptography, quantum communication and it is expected to solve complex problems more effciently than any method within the capabilities of classical scenario. The special issue "Quantum computation and quantum information processing" provides a forum for dissemination of recent results and reviews about various aspects of quantum computation and quantum information. We hope it may contribute to the wider exploitation of quantum sciences and technology in mainstream information engineering. We are grateful to both the authors and referees for their contributions to this special issue. We are also grateful to the chief editor of IJSI, Academician Ruqian Lu, for initiating this project.

    • Distinguishability and Copiability of Programs in General Process Theories

      2014, 8(3-4):209-223.

      Abstract (52524) HTML (0) PDF 227.23 K (2317) Comment (0) Favorites

      Abstract:We propose a notion of state distinguishability that does not refer to probabilities, but rather to the ability of a set of states to serve as programs for a desired set of gates. Using this notion, we reconstruct the structural features of the task of state discrimination, such as the equivalence with cloning and the impossibility to extract information from two non-distinguishable pure states without causing a disturbance. All these features express intrinsic links among operational tasks, which are valid independently of the particular theory under consideration.

    • Positive Aspects of Noise Effect on Quantum Correlations

      2014, 8(3-4):225-240.

      Abstract (1708) HTML (0) PDF 240.90 K (1924) Comment (0) Favorites

      Abstract:Quantum correlations, including entanglement, quantum discord, teleportation fidelity, etc., are resources for quantum information processing. Unavoidable quantum noise usually causes decreasing of quantum correlations, and thus affect the effciency of quantum computation and communication. However, evidences show that proper quantum noise can increase quantum correlations under special conditions. This is because some quantum noise can rebuild the coherence of mixed quantum states. This article reviews the positive aspects of noise effect on quantum correlations, including collective noise, which is caused by several qubits interacting with a common reservoir, as well as individual noise, which is caused by each qubit locally coupled to its own reservoir.

    • Quantum Ensembles and the Statistical Operator: A Tutorial

      2014, 8(3-4):241-253.

      Abstract (1609) HTML (0) PDF 236.47 K (1830) Comment (0) Favorites

      Abstract:The main purpose of this tutorial is to elucidate in details what should be meant by ensemble of states in quantum mechanics, and to properly address the problem of discriminating, exactly or approximately, two different ensembles. To this aim we review the notion and the definition of quantum ensemble as well as its relationships with the concept of statistical operator in quantum mechanics. We point out the implicit assumptions contained in introducing a correspondence between quantum ensembles and the corresponding to single-particle statistical operator, and discuss some issues arising when these assumptions are not satisfied. We review some subtleties leading to apparent paradoxes, and illustrate the role of approximate quantum cloning. In particular, we review some examples of practical interest where different (but equivalent) preparations of a quantum system, i.e. different ensembles corresponding to the same single-particle statistical operator, may be successfully discriminated exploiting multiparticle correlations, or some a priori knowledge about the number of particles in the ensemble.

    • Channel Coupling: Entanglement Preservation via Unentangled Correlations

      2014, 8(3-4):255-264.

      Abstract (1633) HTML (0) PDF 196.28 K (1915) Comment (0) Favorites

      Abstract:Give two quantum channels acting on di?erent systems, we provide a natural and powerful method for coupling them by virtue of correlations between local environments. As an application, we demonstrate, through very simple examples, that separable (unentangled) correlations are a useful resource for preserving entanglement, which otherwise would be completely destroyed by entanglement breaking channels if environmental correlations were absent. This reveals a mechanism for engineering environments in ˉghting decoherence.

    • Fisher Information and Means: Some Questions in the Classical and Quantum Settings

      2014, 8(3-4):265-276.

      Abstract (1572) HTML (0) PDF 228.58 K (1793) Comment (0) Favorites

      Abstract:The algebraic and geometric properties of Fisher information, its relations with the theory of operator means have been very active fields in the last decades. In this paper I try to shed some light on recent results and to address some open questions which could in principle give some new directions to the field.

    • Decorrelating Capabilities and Measurement-Induced Correlations of Unruh Effect in Dirac Field

      2014, 8(3-4):277-288.

      Abstract (1563) HTML (0) PDF 222.54 K (2018) Comment (0) Favorites

      Abstract:We revisit the issue of information transfer induced by Unruh effect in a free Dirac field, where one of the observers (Rob) is uniformly accelerated with respect to his partner (Alice), each holding a mode of a free Dirac field in Minkowski spacetime. We first introduce the information loss induced by Unruh effect when the initial states between the two modes shared by Alice and Rob are any Bell-diagonal states, and give their analytic expressions. Then from the decorrelating capabilities and measurement-induced correlations perspectives, we reinterpret the changes of correlations induced by Unruh effect in Dirac field, which may shed new light on the understanding of Unruh effect from the information theory viewpoint.

    • Detection of k-Partite Entanglement

      2014, 8(3-4):289-297.

      Abstract (1668) HTML (0) PDF 320.60 K (1874) Comment (0) Favorites

      Abstract:In this paper, we investigate k-particle entanglement of arbitrary dimensional multiparticle quantum systems, and obtain several entanglement criteria for mixed multipartite states. According to these entanglement criteria, we obtain a hierarchic classification of all quantum states from fully separable states to genuine entangle states. In addition, we also point out that these criteria can detect some quantum states containing k-partite entanglement which cannot be detected by previous criteria.

    • An Estimate of Quantum Evolution Speed

      2014, 8(3-4):299-307.

      Abstract (1680) HTML (0) PDF 245.67 K (1912) Comment (0) Favorites

      Abstract:The evolution speed of unitary quantum dynamics plays an important role in assessing the maximal speed of quantum computation, quantum information processing, and communication. Here we evaluate the minimal evolution time for a state to decay by a certain amount 2, which is a generalization of the minimum orthogonalization time, and present an improved lower bound expressed in terms of the energy characteristics. We also reveal an intrinsic quantum speed limit for any Hamiltonian.

    • Quantum Pushdown Automata with Classical Stack and Tape Head

      2014, 8(3-4):309-316.

      Abstract (1661) HTML (0) PDF 166.42 K (1744) Comment (0) Favorites

      Abstract:The quantum computational models were proposed to study how quantum mechanics influence the power of computing models. A lot of works are already done to extend simpler classical computational models to quantum models like quantum finite automata[3] and quantum pushdown automata[2,5]. Since the quantum part of a machine is not easy to implement, it is necessary to think about a computational model which minimize the quantum part of the model. Motivated by this fact in this paper we introduce a variation of quantum pushdown automata whose stack and tape head are implemented as classical devices. We observe that this model is powerful than classical pushdown automata and some other quantum computational models. Here we also showed that it can recognize some non context free languages.

    • Geometric Measure of Quantum Entanglement for Multipartite Mixed States

      2014, 8(3-4):317-326.

      Abstract (1720) HTML (0) PDF 209.63 K (2155) Comment (0) Favorites

      Abstract:The geometric measure of quantum entanglement of a pure state, defined by its distance to the set of pure separable states, is extended to multipartite mixed states. We characterize the nearest disentangled mixed state to a given mixed state with respect to the geometric measure by means of a system of equations. The entanglement eigenvalue for a mixed state is introduced. And we show that, for a given mixed state, its nearest disentangled mixed state is associated with its entanglement eigenvalue. Two numerical examples are used to demonstrate the effectiveness of the proposed method.

    • Two Examples on Quantum Control

      2014, 8(3-4):327-337.

      Abstract (1715) HTML (0) PDF 238.40 K (1873) Comment (0) Favorites

      Abstract:With the development of technologies coupled with fundamental scientific inquiry, the quantum control gradually enters into people's horizons. More and more theoretical and experimental researches in this area have been driven. A lot of sophisticated control methods, such as dynamical decoupling and coherent-feedback control, have been proposed. The experience has shown that systematic use of quantum control theory can lead to significant improvements in technologies ranging from magnetic resonance to prototype quantum computers. In this work, we mainly briefly introduce two widely-used quantum control protocols, namely open-loop control and closed-loop control, and illustrate the significant role played by the quantum control using two explicit examples. Obviously, this is only a tip of the iceberg.

    • Quantum Anonymous Ranking with d-level Single-Particle States

      2014, 8(3-4):339-343.

      Abstract (1912) HTML (0) PDF 166.71 K (1994) Comment (0) Favorites

      Abstract:In this paper, a novel quantum anonymous multiparty, multidata ranking (QAMMR) protocol with d-level single-particle states is proposed. Unlike the QKD-basedQAMMR protocol in Ref. [1], the proposed protocol only need to operate single-particlestates without distributing keys among the participants. n(n > 3) participants can correctly and anonymously obtain the rankings of their data, with the help of a semi-honest third party. It is shown that nobody except the participant himself can match the identity with his data by security analysis.